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SYSTEM Al,lf•,LYSIS

For The

Hunts:, i 1 le C-^perat i on 'support CenterDistributed Computer System

(RASA —Ca — 171506) SYSTEM ANALYSIS FOR THE

HUNTSVILLE CFEbATION !j0i?PGB1 CfhTER,01STRIBUIED L08iUTEF SYSTEM Interior REPort,dar. - Jun. 1585 (hisEiEEiEEi State Univ.,eiEsissippi State.) 207 p EC AIJ/hF A01

t,85-28642

UnclasG3/b 2 21493

Interim Report for Period March 1955 through June 1985

.A-NN,UAL REPORT

1985

Submitted by:

D. M .as_ey. Associate In-,est igatorF. M. In gels, Principal Investigator

MI _si =ippi Et ate Univer =_i tElectrical Enaineering Department

Mississippi State, MS 35712'601) —3912

Submitted t]:

NHSA MSFC. AlabamaTechnical Mon it pr: Frank: Emmens, EE332,

(205? 45.3-4629

rJA58-34946

011

SYSTEM ANALYSIS

For The

Hunt i1le Operation Support CenterDistributed Computer System

Interim Peport for Period March 1985 thrc,ugh _Tune

ANNUAL REPORT

1985

Submitted by:

D. Masse y . Associate In iest (ciator.F. M. Inaels. Principal Investigator

Mi =_si__ipp( State Uni.^ers(tyElectrical Engineerinci Department

M (s =- 1 ss 1 pr) i State, MS '9; _?J(601) 325-3912,

Subm(tted t.,;

NASF; MSFC , Alabama.Technical Mon( tor: Frank Emmen _ , EB'32

(205i 453-4029

Nr~S8-34900

C' k,'ER') I El-d OF REPORT

Network Systems Corporation s HYPERchannel netA)orVis a baseband, 50 Megabit per second, high speed localarea network.. HYPERcnannei uti li zes a Carrier SenseMultiple Access (CSMA) data trunk. access protocol, withprior i tized staggered dela y s. . This nett„fork has thecapabilit yof interconnecting various computerresources of differing manufacture, into a singleeft iclent comput i ng fa^illtr.

This. ne twork is currently In use at the Hun tsviIIeOperations Support Center (HOSC). HOSC as a distributedcomputing s ystem, is responsible for data acquisitionand anal ysis during National Weronautics a.nd SpaceAdmir,istration- s (NASA) Space Shuttle operations. HOSCalso provides computing services for Marshall SpaceFlight Center's nMFSC) non -mi ssion actIvItIes.. Amission and non-mission activities chan ge, so do thesupport functions of HOSC change, demonstratinq theneed for some method of simulating activity at HOSC inar lclus contl gurations.

The simulation developed in this ;,fork primarilymodels NSC' s HYPERchanne 1 network, since th is networkbasically determine=_ HOSC's efficiency In accomplishingi ts mission. The model simulates the activit y: of asteady-state ne ti,,jork , repor t I ri g stat i stics such ;= .transmitted bits, collision statistics, tra.me sequence=transmitted, and average me ssa g e de 1 s . Thesestate=t i cs may be useH to evaluate such pertormanceindicators as throughput, utillzat on, and deIay.Thus.the overal 1 performance of the network: ma y bee'lalua t ed, as well as. predlctlnt pos = ible over Icadconditions.

HOI,..I Ti l PEHD THIS PEPC 1RT

Th is report is a full y de t ailed report concerning theinner work.inq_s. of the WPEPchannel Local Area Network.Chapter ” a description of the HOSC system, Chaptera. tuil detailed description of the simulation software(design arch tecLure Chapter =1, 1ndi-.)idual sottwaremodule description I•;ppendlx III); and a presentation ofthe simulation results for sin g le and dua.l trunkoperation, Cha p ter 5. The reader Interested In a. quickg"ery I um and a survey of the HOST- = s tern pertormancemay read Chapter I and Cha p ter 5 onl y . Howe - erknowledge of the HYF'EP,channe 1 adapter's inner work i ngsincluding message frame cons truct.lon and timing 1sdesirable, Chapter

IT _ 1 I V

f0i r ' ''

IN

TABLE OF CONTENTS

Chapter Page

ii k . ! ERU I EW OF PEPORT ....................... i v

TABLE iiF Ci iNTEHTS ................... I ... .

LIST OF TABLES............. .............. .iii

LIST OF FIGURE' .......................... ii+

LIST OF HCPONT'M'= .........................

1 Introduction ............................. 1

1.1 NS-C's WrPERchannel Local AreaNet s.)fork .............................

1 .2 HOSC System 1_1 -ler y l e 1Al. . . . . . . . . . . . . . . . 21.3 Research Objective . . .. ............

2 H7PEPchannel ^Ietl,.jork Description ........ o2. 1 N t ;fork. I omp nen t _ ...... .. ......... .5

2.1.1 Ada pter r,rchitt_ture........... Q

2.2 H'YPERchannel F;otocol=.............. 12

2.2.1 Trij- t --icce=_s Protocol .......... 132. 2.2 Hda p ter -r-;dap ter Li nk: Le u e l

and I .J i rtua.l Ci rcu i t Protocol =-.. 192.2.2.1 Frame and Frame Se.auerce

St ructure .................... 21

2. .2.2 Trunk. Sel__tion.............. 3i+

2.2.2.3 1,)1rtu.a1 C+rcu+tE=.tabIishment ................ 32

2.2.2.4 Data. FIov, Control ............ 3O2._ Intra-Adapter +=ommunica.t+on........ 38

3 HOSC System Description ................. 3P

:.1 T y pical HOSC S y =.tem Act1 1.) it+?=_...... 40

3.2 HC-1 15C System Component =_ .............. 45

N `

Of

Chapter Page

4 Software Design Description .............. 584.1 Software Functions .................. 584.2 Design Constraint =_ .................. 594.3 Design Specifications ............... 59

4.3.1 Simulation Assumptions.......... 59

4.3.2 Parameter Definition............ 604.4 Algorithm Description ............... 62

4.4.1 Overall Simulation Activity..... 62

4.4.2 Model Set-Up .................... 694.5 System Files ........................ 694.6 Reported Statistics ................. 71

4.7 Validation Criteria ................. 72

5 Model Analysis an-' Conclusions...........5.1 Theoretical Performance Bounds. ..5.2 Presentation of Simulat i on^ sults.. 81

5.2.1 Single Trunk HO.1L ­,a=_uits ....... 82

5.2.2 Duai Tn i''„6 HOSC Results......... 975.3 Ana ly sts ana Conclusions ............ 110

APPENDIX I Software Source Listing .............117

APPENDIX II Summary of ISO-OSI Model ofDistributed Networks ................168

APPENDIX III Simulation Software ModuleDescription .........................1691. Siml ............................1692. Initialize ......................1693. CharacterizeNetwork .............1724. PrintNetDescription .............1725. FindNext ........................1726. PickA ...........................1757. Acollision ......................1758. Uniform .........................1769. Update ..........................176

10. Print=_.tats ...................... 17911. Activitysummary .................181

APPENDIX IV Typical Single Trunk SimulationResults .............................183

APPENDIX V Typical Dual Trunk SimulationResults .............................1'ry

REFERENCES AND BIBLIOGRAPHY ......................197

vi

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LIST OF TABLESTables Fage

2.1 HYPERchannel Protocol Frame=_. . . . . . . 22

2.2 Frame Form;. t s . . . . . . . . . . . . . 23

2.1 HCSC Data TransfF-: . . . . . . . . . . 42

3.2 Summ?ry of DEC VAX 11/780 I/OCharacteristics . . . . . . . . . . . . 54

3.3 Summary of Perkin Elmer 3240 I/OCharacteristics . . . . . . . . . . . . 57

5.1 Theoretical Bouncs on a HYPERchannelTrunk of Length 100n Feet. . . . . . . . 77

5.2 Calculation of Parameters us:rgSimulation Statistics . . . . . . . . . 83

5.3 Relative Probabilities of Transmitter/Re=eiver Pairs for Figure 5.1 . . . . . 84

5.4 Data Points for Figure 5.2 . . . . . . . 86

5.5 Data Points for Figure 5.3 . . . . . . . 88

5.6 Relative Probabilities for Transmitter/Receiver Pairs for Figure 5.4. . . . . . 98

5.7 Data Points for Figure 5.5 (Trunk 1) .100

5.8 Data Points for Figure 5.5 (Trunk 2) .101

5.9 Data Points for Figures 5.6 and 5.7 .104

.,

Vii

Qi,

LIST OF FIGURES

Figure Page

2.1 Typical HYPERchannel Interconnection . . . . 7

2.2 Block Diagram of NSC HYPERchannel Adapter. . 11

2.3 HYPERchannel Delay Time Events . . . . . . . 16

2.4 Sampls AD8 Contention Timing Calculations . 19

2.5 Message-Only Frame Sequence . . . . . . . . 25

2.6 Timings for Message-Only Sequences . . . . . 26

2.7 Message-with-Data Frame Sequence . . . . . . 27

2.8 Timings for Message-with Data Sequences . . 28

2.9 Adapter Reservation Scheme . . . . . . . . . 33

3.1 Typical HOSC Configuration . . . . . . . . . 41

3.2 Block Diagram of VAX 11/780 Computer . . . . 47

3.3 Bus Configuration of VAX 11/780 . . . . . . 49

3.4 Block Diagram of PE 3244 . . . . . . . . . . 55

4.1 Message-with-Data Sequence for Simulation. 64

4.2 Flow Dia gram of Simulation Activity. . . 65

4.3 Model Set-Up for Simulation. . . . . . . . . 70

5.1 Single Trunk Simulation Set-Lip . . . . . . . 85

5.2 Plot of Uti1i7ation )ersus Offered Loadfor Single Trunk Simulation . . . . . . . . 87

5.3 Plot of Transmitted Control and Da`a Bitsversus Offered Load for Single TrunkSimulatio n . . . . . . . . . . . . . . . . . 90

5.4 Dual Trunk Simulation Set-!gy p . . . . . . . . 99

VIII

ni

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Figure Page

5.5 Plot of Utilization versus Offered Loadfor Dual Trunk Simulation . . . . . . . . . 102

5.6 Plot of Transmitted Control and Data Bitsversus Offered Load for Dual Trunk (Trunk 1)Simulation . . . . . . . . . . . . . . . . . 105

5.7 Plot of Transmitted Control and Data Bitsversus Offered Load for Dual Trunk (Trunk 2)Simulation . . . . . . . . . . . . . . . . . 106

ix

X

rw

LIST OF ACRONYMS

ASCII Hmerican Standard rode for IntormationInterchange

BDP Data PathBR Bus RequestCHTV Community Hre.a. TelevisionCPU Central Proce=.5Inq UnitCSMA Carrier Sense Flu tiple Hce_sDDP Direct Dat,. PathDEC Digital Equipment CorporatIonDMA Direct Memor y Hcces=_.ECIO Experiment Computer InputiCutputET External TanksFEP Front End Proc=essorHSLN High Speed Local Ne tv)or KHOSC Huntsville Operation Support CenterIiii Input/OutputISO International Standards OrganizationJSC Johnson -;pace Centerk:SC Kennedy Space CenterLPS Launch P r o c e s s

I n a ystem

Mbps Megabits per secondMECCi Main Engine Cut offMER Misaion EvaIua.tion PoomMI PS HI s=_.ion Integration PIannin SystemMPS Main Propulsion Sy_tem1-1SFC Marshal I Space F1 ight renterNHSH Ha.tional Her onautics and Space Administration

h!PP. Non-Processor RequestPJSr He twork S ystems Corporationiii; iiRera.tic na.1 D;ta.OSI Open S y stems InterconnectionPE F'?rkrn El TerPOGO Payload Operations Control CenterRSS Rancae S.atet:: SysternSBI S::nchronous Bacfpl ane InterfaceSP.B Solid Rocket Booster.SSME Space Shuttle Main Engine=.TS Shuttle Transport System!i BA UNIBUS Hdapter1E?US UH I E; IJ Suse - Microsecond

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Chapter 1introduction

1.1 NSC's HYPERchannel Local Area Network

Network Systems Corporation's (NSC) HYPERchannel

local area network is a widely used very high =peed, 50

Megabits per second, digital communications facility.

HYPERchannel utilizes microcomputer-ba=_ed adapters and

standard 75 ohm CATV coaxal cable as data trunks, to

interconnect various computer resources within a

computing installation. There are three types of

adapters (Processor, Device, and Link) used to

interface individual equipment to the network of data

trunks. These adapt-^? r s provide for:

• interconnection of equipment from variousmanufacturers.

• high performance communication `)etweenprocessors.

• a sharing of peripheral systems betweenmultiple processors.

• realistic physical location ofinterconnected equipment.

• increased utilization of interconnectedequipment.

• increased tolerance to individualequipment failures.

Finally, Data movement within a HYPERchannel network is

accomplished by use of frames and frame sequences.

These frames contain the necessar yin+or-matron for

addressing and routing, along with associated user

messages and data. A sophisticated internal protocol

is used to prov i de for contention al 1 oca.t i on , er^or

detection, retransmission allocation, and data

movement. These capabilities provide a reliable

network that is irsensitive to configuration, and

single points of tailure. This internal protocol is

the basis. for HYPERchannel sys"em performance and wi l l

be described further in a subsequent chapter.

1.: HOSC System Overview

The Huntsville Operations Suppo-t Center (HOSC),

AS implemented at the Marshall Space Flight Center

(MSC) in Huntsville, Alabama, is a distributed computer

resource facility. HOSC is designed to provide real

time acquisition, analysis, and display of data during,

National Aeronautics and Space Administration s (NASA)

space missions. HOSC provides =_upport primarily for the

Space Shuttle, Space Telescope, and Space Labo^story

missions. Among the resource =_ available at HOSC are

various large minicomputers and peripherals. A large

portion of these resources are interconnected using

NSC's H`r'PEPr_hannel network. The configuration

flexibility afforded by HYPERchannel provides HOSC with

the ability to adapt to future mission requirements and

also provide =_ MSFC with a large computing facilit y for

non-mission activities.

Data handl1na at HUSC .all y into two main

categories, mission and non-mission activities. Mission

2

it

II

I 11

760

I t

` factivities are those that take place during powered

flight. For example, the space shuttle main engine data

is analyzed by the Main Propulsion System (MPS)

processor, which is also sent to a back up processor

+ simultaneously. Data arrives via direct ground links orI

satellite communication links from the Kennedy Space

Center Firing Room at NASA's Kennedy Space Center (KSC)

in Florida or from NASA's Johnson Space Center (J3C) in

Texas. Services provided by the network during missions

are data analysis and presentation services for HOSC

mission support teams. Non-mission activities are also

provided b , HOSC, one of these s support for the

Payload Operations Control Center (POCC) preplanning

activity. Future expansion at HOSC may include computer

resource support for Digital Equipment Corporation's

interactive graphics data base (ICDS), and XEROX

Corporation's text-processing operation (S?GMA), both

of which, ale non-mission activities_..

I 1.3 Research Objective

NSC's HYPERchannel loc?1 area network is a

sophisticated computer network a)1owing considerable

f lexib11 i ty and adaptabs 1 i ty w th regard to computer

r?sources. HYPEP.channel allows a wide variet yof

minicompu t er, s, not necessarily manufactured by the same

company, to be interconnected in a single or

3 ^

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multi-trunk network. Thus, computer resources which may

be separated by distance or manufacture r ma;: tie

utilized b y one another within this distributed

computer network. HOSC, as a distributed - omputing

facilit y , utilizes HYPERchannel to accomplish the

interconnection of various computer resources. Mission

-equirements imposed on the HOSC, require that it

posses=_ the ability to adapt and change its resources

according to the dictates of a particular mission. The

I( configuration of the HOSC's resources are mission

i dependent and may be readily changed, howe ,)er, the

! effects of those changes cn system performance are no

readily apparent. The data handling capability of the

HYPERchannel r,e twork, and i is performance in -.)ar i ous_

configurations affect HOSC's system performance

directly. With this in mind, the primary goal of the

research effort was the development of a simuI atior.

model of the HYPERchannel network that could be

manipulated to predict and characterize the nehavior of

Ithe HOSC in a variety of scenarios.

The first step in this analysis was an

investigation of the operatinU properties and

characteristics of a HYPERchannel network. In Chapter 2

of this_ aocument, a functional descriptio.7 f

HYPERchannel s detailed with particular errphasi s on

the protocols usFd by the net .lorV. The second step,

4

I^^

2i

9

detailed in Chapter 3, was the characterization of

various computer resources and possible HOSC activity

scenarios. The third step, detailed in Chapter 4, was

the def i n i t i on and deve 1 opmen t of a sof tware model of a

HYPERchannel network. Using this simulation nodel,r

, Esystem parameters were varied to simulate changes tor

the operating environment of the HOSC. Finally, the

results and conclusions of these manipulations to the

simulation model were compiled and anal yzed in order, to

provide some insight into the present and perhaps

future operating characteristics of the HOSC.

5r^

1

1

4

0 Chapter 2HYPERchannel Network Description

2.1 Network Components

Network Systems Corporation'=. (NSC) HYPERchannel

network is a high speed, baseband local area network. A

HYPERchannel network consists of standard Community

Area Television (CATV) coaxial cables ri =-ed as data

trunks and var i ous. adapter =_. to control network' traff i c

flow. These adapters use a carrier sense multiple

access (CSMA) protocol with prioritized, _taggered

delays to implement traffic flow and control . Network

messages generated by an adapter are composed of frames

and are called frame sequences. These messages are

broadcast a)er a given trunk at a fixed rate of 50

Megabits per se c ond, using a phase modulation technique

with a manchester data format, and are received by

network components through nondir • ection.al taps or ports

(Figure 2.1). Netw ork components at. these ports are

known as network adapters, which control access to a

given trunk. A network adapter can be attached to a=_.

man y as four independent network trunks, enabling a

configuration to match a specific instalIa`ion and

provide:

^i

o incremental expansion

o linear interconnect costF-

o no single point of failure

5

1

Figure 2.1 Typical HYPERchannel Interconnection.

7

t

3

NSC manufacture=_. three main type:. of network

adapters: processor, device and link. A processor

adapter interface=_ a computer data channel to the

network of data trunk=.. It serves as buffered data path

between the computer attached, and the trunk ne twork.

i The computer communicates with data buffers in thee

adapter at its owr. rate and asynchronous. with

transmissions on the network trunks. The adapter

provides the necessary formatting and internal protocol

to transmit the c=ontents of its buffers o k!er the

selected network trunk. The processor adapter receives

data from the trunk network and provides status

information to the originator of the data. The computer

at the receiving adapter may then access the data and

p any a=.sociated message in the adapter buffer. NSC has

designated th;s adapter Type as A400 HYPERchannel

adapters, herein referred to as adapter=_.. The device

adapter function:. as a remote channel providing a

? computer data channel for the attachment of peripheral

Ican trr, un i ts. This adapter i s dr i k:,,en b ,., tt:-jork

messages from the data trunks. It receive =_. network

messages cor.tai n i no device commands, data, and control

information. It generates messages c=ontaining status or

device data. The device adapter operates multiple

devices in the same manner as a data channel produced

by a computer manufacturer operates multiple de-.^ices.

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The link adapter is used in pairs to provide

communication between remote HYFERchannel networks. A

link adapter receivirg a network message destinrd for a

remote network transmits thismessage over a wide band

communications link to the remote networK. The link

adapter at the remote location receives this me=_.=age

and retransmits it over its own local network. There

are two type =_ of link adapter=_., the terrestrial link

adapter and the satellite link adapter.

Finally, due io ti-ie nature of the HOSC computing

facility only the processor adapter be included in

the model.

2.1.1 Adapter Architecture

Ee::) adap t er, regardle ss=_. of the type of u-er

equipmen t attached. consists of the fol lowing:

• A Ti,cr:)-processor with 4096words of read-only memory (ROM)

• Storage section (Buffer and Control logic)1024 8-bit bytes of control memory withodd parity

4096 8-bit bytes of buffer memory withodd parity

16 working registers16 trunk registers256 extension registers

• One trunk interface

This portion of an adapter i=_. termed the Nucleus

Adapter. The nucleus adapter has two general

9

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app Ii cat ions, (processor and device adapter) determined

by the type of equipment attached and the necessary

interface required. Thu=_ an adapter consists of a

spec ific device interface and a nuc1 e"s. adapter. The

device interface will then define the particular

adapter type. An adapter can be divided into four main

sections: micro-processor, buffer, and control logic,

trunx interface, and devici or equipmen* interface

(Figure 2.2). The micro--processor has a 4096 16-bit

word read-only in =_.truction memory with a 320 nano=_econd

cycle time. It handles equipment functions and

responses and manages data flow on the direct data path

betwe:. the equipment and the Pda.pte- buffers. The

buffe^ and control 1 ogi c al ong w, th the trunk

interfaces control the high spead trunk transmissions.

It consists of a 1024 8-bit byte control buffer,

normally used to stack control information, and a data

buffer containing x996 or (optionally) 8192 8-bit

b y tes. This section also contains a flag register and

other registers to specify buffer address, length of

data tra.n mission, and network addressing function=_.

The control logic contained in this section allow

concurrent access to memory by both trunk interfaces

and equipment interfaces.. The 100 Mbps buffers allow a

50 Mbps data movement on the data trunks along with a

50 Mbps data movement with the attached equipment. The

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trunk interface board p up to four) contains. the

necessar y transmitting and receiving electronics and

the high speed logic to control the transmission

envelope-check.words, access code, and network address.

Each trunk interface his the ability to generate a. bus-y

or reserved response and contains the logic to control

trunk contention on its attached data trunk. Finally,

the device interface (up to fouri or equipment

interface contains the circuitry needed to interface a.

specific equipment or device to the adapter. This

interface is unique to a given device and determines

the adapter type.

2.2 HYPERchannel Protocols

HYPERchanne1 adapters support trunk selection,

trunk-access, adapter-adapter virtual circuit, and

host-adapter protocols. The trunk selection protocol is_.

based co a cyclic scan of the connected data trunks.

The trunk-,access protocol is of the carrier sense

multiple access (CSMA) type, with ordered priorities

assigned to each adapter. The adapter-ada p ter virtual

circuit ;p rotocol involves connection eadapter

reservation and deadlock avoidance) and data T 1 ow

control. The assumption of a steady state model

precludes inclu=_.ion of the host-adapter protocol since

a host is represented as a fixed rate data source. In

order to understand the impact of the variou s_. protocols

12

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on system performance, they will be described in detail

in the remainder of this section.{

2.2.1 Trunk Access Protocol

HYPERchannel uses a carrier sense multiple access

scheme with prioritized staggered delays to implement a

trunk access protocol. The intention of this scheme is

^Ito:

o ensure that ready adapters defer to on-going transmissions d

o ensure that . • espor.se (acknowledgement)I frames are transmitted without inter-

ference

o provide as much trunk capacity to thehighest priority adapter as it requestsby prioritized access, and provide asmuch capacity to the next highest priorityadapter as it requests, and so on

o sort out collisions without the necessityof generating random retry delays and ensuringthat colliding frames are not involved incollisions when retransmitted.

HYPEP.channel accomplishes this wi tt. four primary

mechanisms: transmitter disable, fixed delay, N delay

7r priori ty del ay, and end de 1 a> . These functions are

implemented on each trunk interface board and can be

idifferent for each trunk attached.

1 Any time the trunk is sensed bus y the adapter

1 tran,^mitter is disabled (unles. it is transmittingi so

that an ongoing transmission will not be interfered

t,,j i t . The fixed de 1 ay per i od i s a de 1 .ay per i od

13

1

following any tra.nsmi lion in which only the receiving

adapter for the last transmission is. allowed to

transmit. This period of time allows a receiving

adapter to respond immediately without being interfered

with by other ready "=_ending adapters". A t,•ansmittirig

adapter which does not receive a response to a

transmission during this period assumes that its last

transmission was to=_.t and wi11 schedule a

retransmission. Following the fixed delay period a

scheduling period begin=.. This period i=_. the N dela y or-

Pr i or i ty delay period and is a unique event for each

adapter on a given trunk. An adap ter '=_ priority delay

is assigned based on the priority (user defined) and

p lacement on the trunk of the adapter, in question.

Following the fixed delay period an adapter ready to

transmit will wait until its priority delay, at which

time it is allowed to transmit without interfe once if

the trunk is idle. If an adapter becomes ready to

transmit during this scheduling period, but after its

priority delay has ex p ired it must wait until i#s

priority delay occurs again or until the end delay

period (defined next) is encountered. The end delay

period occurs if an entire scheduling period passes

without an adapter transmissi or, . After this event a

free-for-all or contention period begins in which any

adapter which become_ read y to transmit may do so. In

114

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1

this. contention period, collisions become possible if

two adapters sense the t'unk idle and attempt to

transmit nearly simultaneously. These v;.rr ious delay

events are implemented in each adapter b y a timer. This

timer is enabled any time the trunk is sensed idle and

begins to count down to its respective delay events. If

at any time the trunk is sensed busy the timer• is

disablad and loaded with the end delay value. As the

timer counts down the fixed delay, priority delay, and

the end delay events are signaled (Figure 2.3).

These delay settings are set into what NSC terms

as contenticn switches (SW1-SW9), located on each trunk

interface board. These contention switches have 16

discrete positions (0 through F'- , with each position

providing 160 nanoseconds of delay. These switches are

grouped i n sets of three switches per parameter. S1.11 ,

SW2 and SW3 are the least-significan' bit po=_i±ion

switches and SW7, SW8 and SW9 are the most-significant

bit position switches. An adapter's fixed delay 1 s set

into switches cSW7, SW4 and SW1), its priorit y delay is

set into switches (SW8, SW5 and SW2) and f nal1y, its

end delay is set into switches (SV > , SW6 and SW3). The

actual setting= for these switches are calculated from

expressions given by NSC. These expressions when

evaIuateJ, yield decimal numbers which are then

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r- f

L_

B r15

16

ocztcw%#. " .. I .. .OF POUR QUALI - Y

1

Iconverted to hexadecimal equivalents. The hexadecimal

equivalents are then et into the contention switches.

When an adapter receives a transmission frame it

will immediately generate and transmit a response

r frame. So that all ready-to-send adapters will not

interfere with this response, the fixed delay period

^I must be such that all adapters will sense the response

before this delay expires. This relation as given by

NSC [N5CSOal is:

Total trunk cableFixed Delay = length (ft.) + 13 C1)

40

This value as calculated will be the same for all

adapters on a given trunk. The priority delay refers to

the period of time uniquely assigned to each adapter on

a trunk. Th y E time period occurs following the fixed

delay period and is determined by the a.dap ter 's

assigned priority and position on the trunk. The

higher, priority adapter is assigned a priority delay

of 0.413 microseconds, this allows sufficient time for

the highest priority adapter to prepare to retransmit

an unacknol.J edged frame pr i or to i is scheduled

transmission time.

17

Z

The priority dela ys for the remaining adapters on the

trunk is given by [NSC80a):

Priority delay of next

Priority = 10 + highest adapter (decimal -)alue)De 1 ay

(2)

+ Cable length (ft.) to next highestpr i or, i ta.dap ter

40

NSC recommends t;iat prioritie s_ should be assigned

sequentially in order +o maximize throughput on the

trunk. The end delay is calculated for each adapter

such that the lowest priority adapter on making a

transmission is sensed b y all other adapters on the

trunk. This is nece=_sar y since an adapter may transmit

immediately when its end delay is signaled (contention

period). This relay is calculated as [NSC:80al:

Priority delay of lowestEnd Delay = 10 + priority adapter (oectmal value)

(3)Cable length (ft.) from this

+ adapter to farthest adapter40

kn example of the use of (1), (2) and (3) is

illustrated in Figure 2.4. The calculations which

follow are performed for unit #25, trunk 0.

18

.... 'r • Jl^^ ..`mow: - _-'_-• CITI

OF f llli It (^ ^: . Y

4001 60011 20011tEnP.11IIAL TFnMItJA10n

10 Wilt #25

n

IMIT x'05

PnIOniT y 0 F1I10.!ITY I Fn1Un1IY 2 PnIOnITY 3

FIXED DELAY -z 2 1316

.,IJ --- z

AC8 MUNK 80AnD

TI -

SWI!C! I SET TI IJO

FIXED DELAY_P n!C nITY O EL AY

END DELAY

f WiFiF7, UN I T 25 U!IIT 13 1 U!I I T (,5

2 8_1 28 2 8 2 8

3 I T 30 3 F

5T 50 62 67

Figure 2.4 ;nmhle AI)f3 Contention TimingCalculations i NC80a J.

19

I

^I

IRr

N;

Fixed delay = 1200 feet + 13 = 43 10 = 2616

_;O

Priority delay= 10 + 3+ 400 =23 10 = 1171640

End delay = 10 + 63 1 0 + SOO = 93 10 = 5D164 0

These values are then aet into the contention switche

located ors the AG8 trunk. interface board as indicated.

Finally, in the access scheme described thus far, the

highest priority adapters could possibly monopolize the

trunk. To prevent this a. de k)ice Known as a wait

flip-flop is implemented in each adapter. This

flip-flop is =et when an adapter transmits ar.d is

cleared avhen the adapter end delay is signaled. When

the flip-flop is set the adapter is prohibited from

transmitting, the intention of this device is to

provide a fair allocation of the trunk. All adapters

are equipped with this device and adap ter =. k:,j i th th i s

fl i p-f 1 op enabl ed ma y coex i st , on the same trunk, ,,ji th

ad?nter=_.who =_.e flip-flop is disabled.

2.2.2 Adapter-Adapter Link Level and Virtual CircuitProtocols

The followinq sections will deal with data

movement and the protocols involved once an adapter has

gained access to the trunk through the trunk access

protocol. The data. 1 i nk protoc=ol may be v i ewed as

20

nom' ter •^ y 1

On

1r'

having two basic information grouping levels. The basic

information unit is the frame and a higher level

grouping is the frame sequence.

2.2.2.1 Frame and Frame Sequence Structure

The smallest unit of information transmitted over

the network i s the frame. There are three cIAsses of

frames: transmission frames, data frames, and response

frames. Tran=mission frames are generally short frames.

(up to 38 b y te =_) used by adapters for signalling and

status exchanges. Table 2.1 lists these frames and

their functions. There are two forms of data frames.

mes_age proper frames and associated data frame=_

following a message proper frame (Figure 2.8). An

adapter receiving a transmission frame, message pr ,per

or a data Yrame will generate and transmit a response

frame. This response frame =r- rv? s to ackiowledge

receipt of a frame and in some cases ^eturns

information to the transmitting adapter. Frame formats

are listed in Table 2.2. Note from Figure 2.2, that the

fixed del? y period is used to initiate transmission of

ether than acknowledgement frames as will be explained.

As stated previously, a higher, revel information

struc ture is achieved by grouping frames toge t! , er into

frame sequences.. All information exchange= occurring on

the network will be in the form of frame sequences.

There are two types of frame sequence used on the

2i

I

t^

1

Table 2.1 HY PERchannel Protocol Frames [Fran 841.

Transmission Frames

Set Reserve - Reserve receiving adapter

Copy Register - Request for- Register information

i Clear Flao 8 - When set, Flag 8 indicates thatthe ada.pter is ready to rece i -.: , e a

1 frame. When clear, it indicatesthat the frame has been received.

Set Flag A - Flag A, when = !?t, indicate= thatC1 ear F1 a q A the receiver will recei-)e

associated data. It is clearedwhen the last block of associateddata is received.

Clear Flag 9 - When set in 'he receiver, Flag gindicate_ that the receiver isready to receive data. When setin the transmitter, it indicatesthat the transmitter is read y tosend data. When cleared in re-cei -)er, it indurate that thedata block has been receil.;ed.When r_leared in the transmitter,it indicates that data can now bstransmitted.

Data and Message Frames

Message Proper - Used to trarsmit host me=s.agF . = oflength less than or equal to 64bytes.

Associated Data - Used to transmit data blocks oflength up to 2 KbYte s.

Re y onse Fr ames

Response - A receiving adapter sends a re-sponse frame for each non-response frame received. :ts pur-pose is to acknowledge receivedtrames or, as in the case of theresponse to a. copy registersfr e.me, to send requested data.

22

^. _^^ 041- ,

1t

Table 2.2 Frame Formats [FRAN821.

1!

Field Lenqth(bytes)

leading s yncs 12-18frame type . . . 1ac=ess cede . . . 2to address . . . 1+ rom address 1function code 2message length 2check word . . . 2trailing s y nc 8 —

Transmission Frame Format

Field Length(bytes)

leading syncs . 3frame type . . . . 1a•:ce ss code . . . . 2to address . . . . 1from address . . . 1function code . . . 2message lenqth . . 2=heck word . . . . 2trai 1 i nci . . . . . 8

Response Frame Format(no data)

Field Length I(bytes)

leading s y ncs . .12-18frame type . . . 1access code . . . 2to address . . . 1from address 1function code 2message length 2check word . . . 2message/data .8-64/

0-2N:message/datacheckword . . . . 2crailinq sync . . 8

Field Length(bytes)

leading syncs 3frame type . . . 1access code . . . 2to address . . . 1from address 1function code 2message length 2check word 2regi sterinformation 2

checkword . . . . 2trailin g sync . . 8

Message Proper and AssociatedData Frame Format

Response Frame Formatcwith data)

22-

24

network: message-only and message-with-data sequences.

A message-onl y sequence is normally used to transmit

short me sage of up to 64 bytes be tl, ,aeen device r- on the

network. The sequence of frames which make up a

message-only sequence are shown in Figures 2.5 and 2.6.

Data is tr.ansrni tted on the network in 2K byte blocks

(optionally 4K byte blocks) in message-with-data frame

sequences, as shown in Figures 2.7 and 2.8.

In order to promote efficient utilization of the

trunk an adapter does not maintain control of the trunk

throughout an entire message-only or mess_-age-with-data.

sequence. An adapter will relinquish the trunk while

performing tasks not requiring the trunk, these periods

are dep i c tea as del ays in the Figures representing +pie

two types of message sequences. After transmitting the

first frame of a sequence the trunk is released. When

the transmitting adapter is ready to continuF

transmitting it must compete with the other adapters

for trunk access.. After regaining access. to the trunk

the adapter will transmit a. cop y register fr..me. if

this frame is transmitted without a collision, the

receiving adapter will sand a response frame to t1)e

sender. Upon receipt of a response frame tine adapter

captures the trunk by tran =.mitting during the fixed

delay period that foI I ows. The trunk is regained

without interference since any ready to send adapter is

f

X1

y

SENDER

Set Reserve

RECEIVER

-bResponse

Copy Regi stersResponse (Inclodesregister information)

w

Message Proper^- Response

Clear Flag 8'Response

Noce: Frames enclosed within bracket are transmitted withoutinterference by beginning their transmission in the fixeddelay R ±r i od .

Figure 2.5 Message-Onl y Frame Sequence IFP.AN841.

25

i

r

64

12

23

74.5

SENDER RECEIVER CHANNEL CHANNEL DURATIONRELEASED HELD (uSEC)

Delay(Prep aratIonto transmit)

Set Reserve

Response

Delay

Copy Registers toResponse(regi^terinformation)

Hessage(64 byte=_.)

Response

Clear Flag 84— Response

Delay 20

Note: Transmission times do not include propagationdelay.

Figure 2.6 Tim i ngs for Message-Only Sequeoces [FR,AN841.

25

w

64

0

Associated

Data Block

20472048

Associated

is

0

Iles=_.age

Proper

SENDER RECEIVERSet Reserve

Response

Copy Regl stern

goResponse (Inc.reg. info.)

Peceive Data(send message)

Response

Set Flag A.4

Clear F1 as 8Response

P

4 Clear Flag 9Response

Copy Registers4 Response (+ reg.)

P.ece i v, Data(send assoc.data)

Response

Clear Flag 9Response

go Clear Flag 9Pesponse

Copy RegistersResponse (+ reg.)

Receive Data _I (send assoc. data)

P1

do Response

Clear Fiag 9 -ResponLe

Clear Flaq_ 9Response -__O_

Clear Flag A—Response

H ote: Frames Iri brackets transmitted without interference bybeginning their transmission in the fixed delay period.

Figure 2.7 Message-with-Data Frar.? Sequence tFRAH 82i.

i

27

I

64

12

23

96.5

64

12

29

34

12

412

M,

SENDER RECEIVER CHANNEL CHANNEL DURATIONRELEASED

HELD

(uSEC)

•,

Preparat i on to transmi t

Set ReserveResponse

Delay

Copy Register pResponse

Message14 — Response

Set Flaq_ AResponse

Clear Flag 8 — wP,espon ^e

Delay

44 -fCl?ar Flag 9Response

De I ay

Copy Register— 10.q Response

Assoc. Data(2Y, bytes)

aw Resoon=_e

Clear Flag 9 0.Response

De 1 ay

--C1 ear Flag 9Response

•Repeat for each data frame •

•

C1e?r Fl?.g A to ^.Response

12Delay

20

Figure 2.8 Timings fc,r Message-with-Data Sequences1 FP.AI 194 1 .

29

.1

V'

Pi,

jprevented from transmitting during the fixed deIai

period. I4 the sequence to be transmitted is a

message-only sequence, control of the trunk is not

jrelinquished until the entire remaining sequence is

transmitted, see Figure 2.6. The timing and duration of

a message-only Cequence is shown in Figure 2.6.

i1 A message-•with-data sequence is preceded b, , a

message-only sequence, follov)ing the tran=_mis.sion of

the message proper the trunk is released, see Figurei

2.7. When the receiver indicates that it is ready to

receive more data by sending a clear flag 9 frame to

the sender, the sender will compete to regain access to

the trunk. Once the sender regains access to the trunk

it wi11 send a copy register frame to the receiver. I4

successful, it will regain control o* the trunk as

described before. Control of the trunk will not be

relinquished until an associated data frame and clear

flag 9 frame are transmitted by the sender. Thi=-.

procesB is repeated for each associated block of data..

Ma.intaininq control of the trunk durinu data frame

transmissions ensures that these f rames are never

involved in collisions, thus only relatively short

frames will ever need retransmission due to col Iisior,

on the truck. The trunk is held durino data fr_.me

transmission b y the sending adapter, by transmitting

synchronization bits during the fixed delay periods

29

ti 'N

r

914;

I following the transmission frames that make up the data

frame sequence. The timing and duration of this

sequence of frames is shown in Figure 2.8. It is

important to note that in all of these sequence

transmissions that during the delay periods, a

transmitting adapter must aIv.axs compete for trunk

access in order to re g ain the trunk.

I

INSC adapters also support an alternate form of

transmission scheme known as the burst mode. In this

4orm of sequence transmission, an adapter will not

i

relinquish the trunk until it completes an entire framei

sequence transmission. According to literature

avaLi I abl e [ FRAN82] , [ FRAN64I t is mode is rare l y used

and will not be detailed in this work.

2.2.2.2 Trunk Selection

Any adapter in a network can be connected to up to

four trunks. Each trunk use- the same trunk .access

protocol and operates independent l y, i.e., each trunk

has a separate interface board within an adapter. The

interface listens for proper Iy addressed incoming

messages and is capable of generating rejection

response frames if its adapter is reserved. An adapter,

having a frame to transmit and contending for a trunk

will scan the trunks. in a specified manner until it

senses a non-busy trunk. The adapter then waits until

the trunk can be captured through the trunk access

j

20

I ^

A=It - .^ L

I

11

protocol. It the trunk is bus y with the adapter' =_ frame

transmission its search terminates; otheru,ise it

continues. Trunks to be t. . ed ._..- _ __ -1 - : - = i ri _

host — adapter message and a receiver's trunks to try may

be specified by the transmitting adapter. A trunk is

said to be disabled if it is not connected or was not

specified as a trunk to try. A t runk is _.aid to be

enabled if it is connected or is specified as G trunk

to try. An adapter will try a trunk by first

Determining whether it is enabled or disabled, if the

trunk i= disabled or bus y it will try the next trunk.

If the trunk is enabled then the adapter determines

whether or not it is bus-. The period o4 time required

to t.r y an enabled trunk is 5.5 mi crosec_onds, suh i 1 e the

time required to try a di=_abled trunk it 2

microseconds. The ability to specify the trunk=_ to try

i n the tr ansm i t ter and rece i . : er prow i d; s a me an to

dedicate trunk=_. to specific types of traffic, e.g.,

= p ort tr ansm i ss i ons on one, long tr?nsmi =_sion E on

Another. Simulation stud i es indicate no benefit is

derived from dedicating trunks for particular message

types. The RbiIity to speci4 y trunks is more useful in

multi trunk net1,.iorks that are not ful l r connected

[FPANd43. It is possible for an adapter connected to

more than one trunk to recei ­? mesaaae= sirnul taneou:IY,

when this happens the adapter wi11 accept c. re end

1

reject the others. Communication between adapters on

tvio different trunks, require=_ the _er l) i c p s of an

intermediary. One of the adapters will transmit to a

device attached to an adapter common to Do`.h trunks.

Once this device has received this me=s?Qe sequence it

will then proceed to transmit the sequence to thrf

intended receiver on the other trunk, Thus

communication beti.jeen adapter= on different trunks

consists of sending a message-with-da.ta sequence twice.

2.2.2.3 Virtual Circuit Establishment

An adapter reservation scheme (Figure 2.9) is used

to establish a virtual connection t.eth.ieen adapters

d,?siring to communicate. I;jhen an adapter receives

message from i t at t?shed host . i t w 1 1 f i r s t reser'_Je

itself; that is, the adapter makes itseif inaccessible

tcl recei -red tritnsmi =_s i on 4r•nm any other adapter wi t

the exception of the adapter with which it -s trying t^

communicate. Af`:er reserving Itself, the =_ending

adapter transmi t s a 5°t reser')e frame to the receiving

adapter. if the re=eiv;ng ?adapter is idle; that is, it

is no* reserved, then the rece i -) i ng ada.p ter wi 1 1

transmit a re =_ponse f ,-ame indicating that the adapter

has reserved itself to receive a transmission from the

transmuting adap+.er. Following the reservation of I

receiver, the frame sequence transmission proceeds as

described in section 2.2.2.1. Both the transm+ttinc, and

32

/i5g. NoC f rom

OS^

reserve self

initialize:delav :=1usI.etry n

Figure 2.9 Adapter Peservation Scheme [PR N82f.

4

•

1

t

\ i

receiving adapter =_. Terrain reserved d;jririg the entire

message-only or message - -A' -Lh -data frame sequence

t^an sin i=-.=-i or, . Af t er completing the frame sequence

tran=-mission, the t - ansmitting adapter releases tine

rece i u i ng adapter vii th a c 1 ear f i ag A frame :xnd then

releases itself completing The termination of the

connec t i on ; =_.ee 7 i gure 2.6 ar,d 2. 8.

When a transmitting adapter sends a set reserve

frame to a reserved adapter, the reserved adapte r w i 1 1

respond with a reservation reject frame. The r'irst tim.-

a sending adapter receives •a reservation re;ect frame,

the adapter wiI; delay for a "binary exponential time"

before mak i n another re ser ,.,-.t i o-i at temp t . Fol 1 ow i n

the first reser k.l.at i on re.j ec t i nn the adapte r, wi 1 1 de 1 a.y

I mi crosec ond before making a second attempt. For each

following reservation re.jec"_ion, the adapter will de l, 3y

an amount of time egcal to twice thb previous de1 z;y, up

to 128 microseconds. When this value Q+ dela y (128

micro =_econd=.) is exceeded retry i= advanced by ane, the

delay is reinitialized, and the sequence is repeated

(Figure 2.9). This proces s_ will continue until 3ither a

successful reser ,. , ation occurs or the ada p ter's i,etry

cc,ur,t is exceeded. An adapter`s retry count is base,] on

its unit number, manually set by the uBer and is in the

range of C5 to 250 , If of ter re-..r), count tr i es t`le

adapter is un at) Ie to reserve the r^,cei,:)er, the

!•

<M

I

^4

1

0

transmission is aborted and the senner returns to the

idle state. The s.endinq adapter remains reserved

th r, ouahout the entire reservation attempt p roces s_. This

reserva.t on scheme ,)itt the bi nar> exponential delay=

between transmissions, serves as congestion control on

the net^;^ork b y keeping a send 1nq adapter fro,

manop-lizing the network.

T:, is retry scheme as descr i bed has the potent i al

of causing adap cer deadlock.. Th i s wi 1 1 occur ; f ti--,,a

adapters a t tempt t4 rese rve each other n w 1

simultaneously. They will find each other reserved and

qo throu rth the retry scheme until c.-ne or the other's

retr; • count is exceeded and aborts the attempted

transmission. To al 1 ev i ate this probe em, x back.-off

scheme is scrap 1 oyed by commun i cat i ng adap ter s. Th i s

back-off rijutine enabler, a send ,nq adapter to determine

the identity of the adapter that the rejecting adapter

is att? r ipt inq to reserver ,rc•m th .2 j e C t reswon =_e. It

the sending ada p ter determines that it and the

rejec t i nii adap ter are it }emp t i n to reserk)e one

another, then the sending ada p tsr aborts its

reservation attempt a^d relea=_es itself. The s1 own e=_.s

of this back-off mechanism can cause both adapter= to

abort their reservation attempts, preventin•: _•i the r

adapter frorr. cor.municatirig on the network. The time

35

ta

required for this mechanism to respond is dependent on

the adi .oter model and i= aporoximatel, v bG microseconds.

H second form of deadl cc V. ,,.jh i c the back—off

mechanism will not c.rrect is called a reservation

request loop. This occurs when three or more adapters

attempt to reser-.-P each other,i.e., adapter A attempts

to reserve adapter B, !hile p attempts t•:) reserve C,

and C attempts to r^•^,.ve A. In th^s ca=e the adapters

ha ,e no wa of •iP ;erm i n i n p that this s i teat i on exists

and each adapter w^ l i perform the r e _.ervat i on r e t r y

scheme as nrev l ousl ;/ de scr i bad. This deadlock wi l l onl ;,

be rs so v e d Nh r One of tht? adap -ter' s re try cou p t

expires, causing the adapter to abort :is reservat i on

attempt and re I eaae itself. Serious degradation C

trunk t;iroughput ma y be predic`ed during this

reser , . , at i on rPque=_ I pop per i o IDUP&J793 .

2.2.2.4 Data F l ow Control

Network adapter's are suppl ied with tvjo 2E: byte

buffers c4K. b/te buffers optional.). 40i t two buffers

mane ca.n be f i 1 1 ed/emptied b y tr .ans . fer +r Om/ to trieI

attached host, while the other buffer is emptied/filled

by a network transmission reception. In order to en:.ure

that buffer capac i t y i s not exceeded, a f low control

mechan i =,m i needed. Flow control is ach i e-)ed in tvjo

ways. First, data frame length is limited to adapter

bu++er length. Secc nd, an adapter, =.ending a data frame

a ,.R

L

nor

1

^ ly

4 4^

.:,a

may not send another data -r'rame anti the receiving

adapter specifically requests it. This ensures that an

adapter will not receive da.ta fr?.mss at a rate taster

than an adapter may process them.

Additional techniques used b y adapter to prevent

them from becoming permanently blocked awaiting receipt

of a respon =_.e frame which wi'.1 never' arrive are

described in the fo11owing One of the techniques

involved is the requirement that response trames. begin

their transmission during `he fixed delay period. If an

adapter does not race i v. - a response to a transmi s si ors

it will reschedule the transmission at a later time. ro

Ensurr e that all adapter does no* retransmit

indefinitel y , as viouId be the case if the receiver

address were incorrect or the receiver was.

malfunctioning, a limit is p1aceu on the number of

retransmissions aIIol.,eed. A sct reserve frame will be

transmitted 16 times on each trunk anf-1 then aborted if

no response is received. All other frames wil l be

transmitted 256 tines beTore abort, For the case when

the expec fed re{.ponce i s a non-response -frame i c l ear

flag 9 granting permission to transmit data) a "deaama.n

timer" is used. In a tran_.mitting adapter this time

f; same spans the time from ,,,hen the host's transmi t

message is receive until the last butter i

transmitted and acknowledged. In the receiving adapter

37

i

2ii_

this time begins with the rNceipt of a set reserve

f. ame and doesriot end unti 1 the re: .- ipt of the last

data. buffer. This time span ranges fic•m ,5 to 8

seconds, adjustable in second increment =_-. If all

frame transmissions are not completed before this timer

expires, the transmission i=_. aborted [FRANe2].

2.3 In"ra —Adapte r- Communication

A message transfer betweer, attached hosts on the

same ada p ter is termed an intra — adapter rransfer and i

carried ou`. entirely local to the adapter. This Type of

data transter occurs without utilizing the data trunK

network. An im p ortant consequence rit this type of

transfe f, is that the ad<.pter will appear reserved to

the rest of the n p twork . Obv i ousl , , if the occurrence

of this type of transfer becomes p^edominate then

network performance will suffer. If resources do not

conflict, intra—adapter communication may occur

concurr?ntly with network traffic and cause no

degr_adat i on of netl,,)ork: performance .

}Y

4

W

im

Chapter 3i HOSC System Description

As pr,^viou s-1y stated, HOSC is a distributed

computer network employing many large mini—computers

and NSC's HYPERchaniiel network. The primary task of

HG i_-'C is to provide NASA scientists and engineers withi

near real time acquisition and analysis cf data duringk

Space Shuttle operations. This information a.l 1 ows MSFC

engineers and cen tr 3c for personnel to act in a support

ca p acity to other mission specialists at KSC and JSC.

Some of the primary monitoring and support requirement=_.

of HOSC are pre — launch support -for the Space Shut,.Ie

Main Engine (S,,--,ME), the Externa l Tanks (..ET), the Solid

Rocket Boosters tiSRB's), the Main Propulsion Systems

(MPS), ana the R any e Safety System (RSS). Further,

sup p ort is provided for mission e::periments designed by

MSFC personnel.

NASA has defined the mission of the Flioht

Operations Support Center at HOSC as follows:

During pov!ered f1ight, the HOSC willreceive only data which is in the LPS (LaunchPr_ ,ces.sirig SS ten) at KSC. The shuttlesupport tears 1&6 1 1 be i n the HOSC during thisphase of the mi=".:ior, ano will be th? point ofcontact with the JSC Mission EvA-1uation Roomf.MER) for prc,bl em 6 i =- .cus s- i on and reso1 u t i orgyas required and will be on call duringoroi tai operations_.. The Space L:b andexperiment support team will be located inthe HOSC dur i rig orb tai operations L•jt,enapplicable.

05.

i

Fol Ioiuing completion of the activeShuttle vehicla support activities, data isrecalled as required for more detailedanalysis, and initial preparation is made toprovide support to post flight evaluation[NASA82].

HOSC is located in the west end of A-wind building

4663, at MSFC in Huntsville, Alabama. Figure 3.1 shows

the functional com p onents of one of many HOSC system

configurations. The information contained in the

following =_actions of Chapter 3, is from previous work

published in connection with this same research effort

IMAUL841

3.1 Typical HOSC System Activities

The data processing activities at HOSC can be

placed into two categories, routine d a i I v activities

and missicn/launch activities. A summar y of these

activities by category ar.d some details c' f t ypical data

transfers are outiined in Table 3.1. While this table

and the de =_criptior, that +o I I ows, de s cribe typical

?c t i v i t i es, these are not al 1 the act i v i t i es that HOSC

is. enuaoed in. There are some activities that a.re

defined only for a current mission, i.e., experiment

directed by HOSIC mission spec i :klists. Since these may

change from mission to mission they are not included in

the fol lowing description, but must be characterized

and considered in the specific mission scenario

-equired for the total system analysis.

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TNBLE 3 . 1 HOSC Data Transfers

1. ROUTINE DAILY P.CTIVITIESA. POCC Activity

Resources Invol^)eri: MPS Primary (VAX 4)MPS Backup (VAX 1)

Quantity of Data: 1500"100 512-b y te blocks intwo components. 6 8344-byteblocks and 100,000 512-byteblocks.

E. ECIO Data Stream .Generated b y ROMResources I nvul ved: MPS Backup :VAX 1 )

Spacelab °/32

Quantit y of Data: 51.2 kilobyte per secondstream concurrent with POCC.

^fC. IGDS/SIGMA Active ties (Proposed?

Resources Involved: T,_. be determined

aQuantity of Data: Unknovjn .

f' II. ROUTINE LAUNCH ACTIVITIES

H. Routine Dai ly P7t1 l ji ties (Ses Item I.)

B. Main Engine DataResource =_ Involved: STS Prlma.ry (PE 3244)

MPS Backup (':!AX I )

Quanti t y of Dai.?:

C. OD Data StreamP.?sources Involved:

Ouant i t y of Data

50 kilobit per second stream(Launch minus 8 hours untilMEC0)

FEP SSME PE 3244)Cti0 Computer

'T'=- Pr i mart' PE 3244)MPS Backup (VAX 1)

192 k 1 1 obit aer secoridstream into FEP and then toCSO w t Iran=_ter r•f 40percent to STS P-imary andMF Backup. (Launch minusseconds antil MECO)

D. Engineering Displa y ChangesPe_.ourcos Invol ved: STS Primary (PE 3244)

STS Bac=kup (PE 9/32)'Dpacelab 8/32 :PE 2/32)

vuantl t y of Data: Insignificant.

4242 1

-Qi• .

^I

Ore activity not associat:d directl y with the

real-time responsibilities of the network and therefore

a routine daily activity is POCC simulation activity.

The impact of POCC activity on overall performance of

the network stern s_ from the requirement of continuous_

data transfers between network computers. This data i5 ,

currently being transferred be t1,,)een the MPS primary

computer ( I)AX 4) and the MPS backup computer (VAX 1 ) .

During each twenty-four-hour period, this activity

requires the transfer of 150,000 512-byte blocks of

data. This data i s transferred in two components; six

t i m e s each day, ?.n 8344-byte black i s transferred

(50,000 bytes cumulative, with another 100,000

5 112--byte blocks transmitted randoml y but distributed

ievenly throughout the day.

POCC also generates a continual 51.2 kilobit per

second data stream known as the Experiment Computer

Input/Output (ECI0) data stream. Thi s_. data stream is_

ongoing and concurrent with POCC activity. ECIO data is

transferred from the MPS Backup Computer !VAX I) to the

Spacelab 8/32 (PE 8/32c).

The rOLI tine components of the launch day data

activities a.r ,? the Main Engine Data Stream, the

Operat i onal Data (OD) StrFarri, ar,d the E n g i n e e r i nu

D i spla y Change regUests. The Main Engine Data is

collected and disseminated on launch day only. Data i.

43

i

.- • _ _ As

.a.

W'

funneled thro:,gh the network to the MPS Backup Computer

(VAX 1) from the Shutt1A Transport System (STS)

Computer "IPE 7--,, 244). From eight hours before launch

until about twelk.e minutes after launch at Main Engine

'ut Off (MECO) 9 STS Primary accepts. a continuous 50

kilobit per second lata stream direct1;• from the KSC

Firing Room and transfers about 24 percent (12 kilobits

per second) of the total stream to MPS Backup.

The OD Stream is a. 151- kilobit per second data

stream arriving at the Front End P-ocessor Space

Shuttle Main Engine 'FFP SSME) Computer (PE 3244) on

launch day concurrently with some of the Main Enr^inN

Data (launch minus 4 seconds. until ME.CO). This data

arrives from Goddard Space F1ignt Center in Mar land,

and is transferred over the network. ho +h•_ CSO

facility.

The Engineering Di=pla y Change activit y is an

a ! most insignificant addition to the total network

traffic. This activity i nvol ves a transfer from STS

Primar y to STS Backup and Space 1 ab E/32. Th i s tr an_.fer

consists of the name of each engineering con =-ole format

in the support facility that is changer s luring the

prelaunch and launch period (launch minus 9 second =_ to

MECO) [MAUL84].

44

i

R

3.2 HQSC System Components

The Hunt=k p iIle Operations Support Center as a

distributed computer facility uses various computer

^esources interconnected together. The basic components.

involved at HQSC are the computers, communications

processors that receive data from wideband

communications links (sate IIite and terrestrial) and

the h^;.vdwarP recu i red to i nterconnec t these v a r i cw

resources, The inte-.connecting hardware. Network

Systems Corporation's WYPERchannel network, has. been

i previously described, and interconnects a variety of

computer resources of different manufacture, i.r

Digital Equipment Corporation (DEC), Perkin—Elmer (Pr),

and UHIVAC. The bulk o+ the processing power for the

netiuork i performed by the DEC VAX and PE :3240

computer=_.. A cursor y look kUili be given to these two

computers. These computers are examined for the sake of

information only, since in the subsequent anal ys_ is e.11

network users will be represented as fixed rate data

generators.

The Digital Equipment Corporation's VAX serie s c14

computers supports a 32—bit ,,lord architecture that

estaol i s-he= at v i r tua.I address, space of 4.? bi 1 1 ion

b y tes of user — addressatie memor y . Throughput of data in

the system is optim i zed by using a 32 —bit high _peed

data structure that ties together the central

4

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1.,1

processor, main memory, UNIBUS subsystem, MAC38 US

subsystem and the DR780 high spec-d direct memory ;.cce

subsystem. This high speed data structure is known as

the ° y nchronous BackpIar+e Interface (SEI) and a device

linked to it is known as a NEXUS. Each NEXUS receives

every SE tre.nsfer ; e l ec tron i s l og i s i n the I?EXUS

determines whether it is the designated receiver for

the ongoi inq transfer . Data transfers. can occur from CPII

to memory, from I/O controller to memory subsystem, or

from CPU to I/O controller, with maximum aggreg -ate

transfer rates of 13.3 megabytes per second. These

transfer rates are 1 imi ted by the following factor-.:

0 260 nanoseconds/c ycle = 5 million cyclesper, second

• each cycle can carry an entire byte ofdata or address representing a memoryrequest

• one cycle is used to request eight bytesof data to he r ead or a+r i t ten , and twocycles are used to carry data at fourbytes per cycle

o ° million cycles/second e 4 by tes/eyrle =20 million bytes/second

0 20 * 2/3 (1 of every 3 cycles is anaddress) = 13.3 million by tes per second1DEC803

As is sho+^jn in Figure 3.2 , a VAX computer ma,,

interface with more tear, one memor y subsystem. !r the

Case of a two-controller, interleaved memc.ry

46

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con+ i gurat i on , the compu ter wou 1 d al so have two PIEYUS

memory controllers on the SBI.

The IINIBUS Subsystem (UBUS) is. a high speed,

as ynchronous data system that allows communication

between peripheral hardware and the VAX computer. The

VAX. 111780 is capable of supporting four UBUSes: one is

standard, but three more are optional (Figure 3.3). The

UBUS is connected to the 36I through a UBUS Adapter

(UBA) i.,jh i ch perform s_ se ,.,eral impor . tar, t se r- i ces that

are transparent to the user. The UBA provides:

• access to UBUS address space from the SBI

• mapping of the UBUS addresses to SBIaddresses for the direct memory access(DMA) transfers to the system memory

• data transfer paths for UNIBUS deviceaccess to random SBI memory addressesand high speed transfer for devices thattransfer to consecutive, increasingaddresses

• UNIBUS interrupt fielding

• UNIBUS priority arbitration

The address-mapping function is especially

important because the UBI_I S ha.s or, l; eighteen data 1 ine=_.

providing an apparent memory-addressing capabilit y of

only 200 kilo- bytes. Through it=_ addres s_ mapping

a.bi 1 ities, the UBA prok)i des the c3.pabi 1 i ty of mappinq

the UNIBUS adcres s_es. into the SBI addresses so that the

48

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fu I 1 sys tem memor y of 16 array boards of 256 K i 1 obytes

each (A gigabytes total) can be accessed.

The UBA accept =_ two forms of input from the !;BIIS:

hardware-generated interrupts and direct memory access

requests. Each device connected to the UEUS may use one

of five priority levels for requesting bus service. A

non-processor request (NPR), which is the hi ghest

priority request, may be used when the device request=

an operation that does not require proce_sor

intervention, such as a direct memory access transfer

to memory or to some other . device. A bus request (BR)

is thus generated when the device wishes to interrupt

the UBA for service. Such service might be a

CPU-directed data transfer or A flig indicating the

existence of an error condition at the peripheral.

Since there are only five priorit y levels and more than

c. r, dev I ce may be connected to a spec i f i c request

1 eve 1 , i f more than one dev i ce makes the same requesi ,

the device that i s_ electrically closest to the UBH

receive =_ the highest priority.

The NPR request for direct memory acces s_ is a very

important feature of the IJBUS subsystem. These DMA

transfers car, be divided into two group s_.: random access

of noncontiguous addresses and sequential access of

s_.equentially increa - ing addresses. For random access.

each UBUs transfer is made through the Direct Data Path

50

1

Ow ,

(DDP, one per UBUS) and is mapped into an SBI transfer.

This procedure allows only one word of data to be

transferred during a single SBI cycle. For devices

capable of requesting s equential access s ervices, use

is made of the Buffered Data Path (BOP). Each UNI BUS

provides fifteen such BDPs which storo the data so that

four UBUS transfer= are performed for each SBI

transter.

The DDP must be used b y devices• not transferr i nq

to consecutively increasing addresses or by devices

that mix read and write functions. The maximum

throughput via the DDP is about 425 ki1ov)ords per

second for write operations and about 316 kiloword=_. per

second for each read operation. These rates will

decrease as other -SBI activity increa.=__es. [DEC801.

Maximum published throughput via the BDP is about

65' 5 k i 1 owords per s econds for both the read and u,r i to

operations, but realistic throughput rates of onl y 1.5

megabits per second are actually expected 1;.iith this.

figure degrading as other SBI activity increase_. BDP

tra p=_.fern are restricted to block tran=_.fer with blocks.

of length greater than one byte. All trans-'ers vii th i n

the bI ock mu =_ . t be to con=_.ecut i ,Jr and increa si n g

addresses and all transfers must be of the same

function, either read or- wri te.

f^

51

1

Li

The MASSBUS subsystem and the DR780 high

p erforma,-ice, 32—bi t par.al let interface wi l l not be

described in this summary, since an understanding cf

their functional characteristic-- is not needed to

determine their relative impacts on the HYPERchannel

network. The influence of both may be felt indirectly,

hol:,jever, since activity on the MAS8BUS or DR -7130 will

translate to SBI activity which will affect GDP and BDP

transfer rates as previously described.

1 The VAX CPU will also not be described in detail

but several comments may be made about the CPU and it=__

effects on system throughput. The CPU represents the

r o t s c c t Pmost intensive tratf i c l oad n h? memory ub_;.^: m in ik

hence on the SBI. Obviously, it the processor is

l engaged in intensive competing, it will request data

ff much more often than i t o-j1 1 1 wr i to data, and th i s

memory access r ,?pre =_ents substantial SBI activity.

Fortunatel y , the large cache memory of eight kilobytes

ava.i 1 abl e to the CPU is able to reduce the SBI tr-.=-L++ i c

load considerably. In addition to the effects of the

CPU on SBI activity, the SBi traffic from other sources

may also affect the CPU efficiency. Published figur?s,

IDEC3Ul, indicate that in a system with two memory

controllers the processor will be sla:-jed by about four

percent per averaged megabyte per second of I/O

traffic, while the impact of a single memory controller

52

Z1

is to slow the processor by a factor varying from two

to four. Table 3.2 summarizes the I/O characteristics

of the DEC AJAX 11/7$0 processing system.

The Perkin Elmer 3240 series c,f computers is also

a high throughput machine with a 32-bit architecture.

The HOSC currently uses two PE 3244 machines with

primary responsibilities as front end processors

r•ece i v i ng real -t ime data streamsfrorrti the KSC f i r i ng

W room.

1 The 3^244 memory subsystem is organized into banks,t

each capable of handling four megabytes of addressable

memory. Total system memory range =_ from 21 56 kiIobytes

in one bank to a full system complement of four

4-megabyte banks, for a maximum of 16 megabytes of

addressable memory. All memory is connec-ed to a common

memory bu=_. which consist=_ of two unidirectional,

asynchronous, 32-bit busses. One bus is dedicated to

memory write functions and the other i =_. dedicated to

memory read functions (Figure 3.4).

Input/Output is accompl ished using fine external

communication busses: one multiplexer bus for medium

=_•peed devices and a maximum of four high-speed Direct

Memory Access (DMA) bus=es that each support eight high

speed bidirectional ports. Each DMA port is controlled

b y a selector channel tied to the multiplexer bus that

controls and terminates transfers through the CPU. Once

v

53

t.

5N

TABLE 3.2 Summary o4 DEC VAX 11/780 I/OCharacter i st i cs

E!

Processor:

32-bit vicird architecture

Main Memory:

Virtual address space:

Cycle Times:

4.3' billion bytes..

800 nanoseconds per 64bit read.1400 nanosecond=_. per 44bit write.

I/O UNIBUS Adapter

Maximum aggregate rate:

1.5 Mb y te/sec throughBPD

Buttered Data Paths (BPD'): 15 total, 8 b y te butteri n e ac h, 695 k i t ovior dsper second read andwrite. Used for fastdata transters.

Direct Data Path (DDP) 425 k: i 1 ov.)or ds/sec forv.ir i to and 316 k. i 1 ov.jords.per second +or read.Used for tran +ers tononconsecutive memorylocation_..

54

I

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^I — — ------- KWUI

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tIC ----------- LMC

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Figure 3.4 Block Diagram of PE 3244.

55

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56

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the channel is activated, the processor is reIeased and

is free to continue processing on an unrelated task.

Published I/O transfer rates for the PE 3244 [-MA bus

indicate that transfer rates of up to 10 megabyte =_ per

second i n the burst mode are possi bl e for each DMA bus

[PEC81I. The I/O characteristics of the PE 3240 series

is summarized in Table 3.3 [MAL ►L84].

to

0E

TABLE 3.3 Summary of Perkin Elmer 3240 I/OCharacteristics

Processor:

32 bit/word.

F Main Memory:

V i rtual Address pace:

lb Megabytes.

Cycle Time:

500 nanoseconds.

DMA Bus Data Transfer Rate

Burst Mode: 10 Megabytes persecond with a maximumof 4 DMA busses per/stem.

57

1

1

:.

Chapter 4Software Design Description

This• chapter describes the development of the

software used to model the HYPEP.channel network. The

intent of the simulation is to accurately model the

characteristics of a HYPEP.channe 1 network. Wh i 1 e, every

possible function of the network is. not characterized,

the protocols which have the most impact on the network

were included to the extent possible. The goal of the

simulation is to provide a software tool to analyze the

characteristics of present and future configurations of

the network at HOSC.

4.1 Software Functions

The simulation model as de v eloped should perform

some primary functions, among these are:

1) provide a relatively easy method ofsimulating the existing system andprovide a means for modifying thesimulation environment so that differentconfigurations may be modeled.

2) provide an output which may be meaning-fully converted to performailLe measuresdescribed in this Chapter and Chapter 5.

3) provide a user friendly interface at alllevels of user interaction.

The so+tware should be designed to be as portable as

possible so that transferral from the development

compu`er to other computer environments should be

accomplished as easily as possible. Also, an;, future

56 I

a

CD

Iii enhancements of the algorithm as designed, should have

the capability of being accomoIished as easily as

possible.

Finally, the development of this simulation as

related to the ISO-OSI model for distributed computer

processing (Appendix II), ma y be thought of, as having

been developed between levels S and 6, the Session and

Presentation levels.

4.2 Design Constraints

The primary design constraint placed on this

imuIation effort was that the simulation be as

transportable ?.s pos_.ib1? between ccrrpUter:

unspecitied size and capabilities. `herefore,

I A.nguaae PASCAL w as chosen due to its vii de=_pre :^. d

availabilit y and richness of data structures.

4.3 Design Specifications

This sec tion deals wi`.h the imposed constraints

an^J assumptions which the model uses to ?.ccemplish its

simulation activity. These assumptions were mode to

keep the model both realistic and manageable.

4.3.1 Simulation Assumptions

In order to maintain viabilit y and model validity

certain assumptions were made. These assumptions ?re a^:

follows:

59

rm

v

1r• N

Qir

i

r

1) Every time an adapter regijests thetrunk, the frame sequence sent is amessage-with-data sequence. Therefore,message-only sequences are excluded.

2) Maximum number of trunks is two.

3) Model will reduce to a single trunkmodel.

4) Any single adapter may be attached toboth trunks (dual trunk model)(1,2,..,N)

5) Trunk lengths are less than, or aqua to1000 feet, Belden 9248 cable data isused (propagation time).

6) Worst case fixed delay, priority deiay,and end delay will be used, as given by(FRAN841.

7) In order for the -,cdel to resemblereality as closely as possible, measuredtransmission frame times will be used(CWAT5821,CFRAN821).

8) Intra-adapter communication is notallowed.

9) The wait flip-flop option is notimplemented.

4.3.2 Parameter Definition

As previou_ly stated worst c^-=e value_ _,f fixed

rela y , priority delay, and end delay are a=ed in the

si m u l ati on . The expression used to evaluate the fixed

dela y on a given trunk is given by:

Fixed dela y = 4 nsec * (trunk 1errath) + 2.08 user (1)

where trunk length is given in +eet. This value

approximate , but is greater than, ti.-lice the end-to-end

60

propagation time for the trunk, plus the time required

by the adapter to formulate and to begin transmitting a

response. This value is the same for each adapter on a

given trunk.

The highest priority adapter i E assigned a

priority delay of 0.48 user. The priority delay for the

remaining adapter=_. on a liven t r unk is given by:

Priority delay (K) = Priority dela y -:K-1)+ 4 ne.ec * d + 1.6 u=_.ec, (2)

K = 2,3,....L

where K is the index of the adapter with priority K and

d is the distance in feet betvieen the adapter kvith

priority K and the adapter with priority (K-1), L

refsrs to the lowest priority adapter. The constant 1.5

u=.ecs i S added to al1e ,)iate oroblems with line

rzflections.

The end dela y of the adapter with priority K i

given by:

End dela y ( K) = Priority delay (L)

+ nsec * d + 1.6 u , ec. (3)

K = 1,2,....L

where L is the lowest priori ty adapter , and d i s the

distance, in feet, from the adapter tjitti priority K to

the adapter farthest from i t [FRHl\184] .

61

i1

-- 'FF

n1 w

These are the rrajo; parameters ujh i ch need to be

calculated for a given configuration of the

HYPERcha.nne 1 network . They are cal cu 1 ated for , ai ven

configuration when the simulation p rogram is executed.

4.4 Algorithm Description

In this section an overall view of the activit y of

the simulation is detailed. Detailed descriptions of

the individual module=_. used by the program are found in

Appendix III.

4.4.1 Overall Simulation Activity

The simulation as developed is a discrete ek.)ent

simulation. The event that drives. the model iE^ an

adapter's next scheduled transmit time. An adapter

trying to transmit will at tempt to obtain a. trunk in

three given time frames. An adapter ma y try to transmit

while the trunk i=_ busy, during the priority delay or

scheduling period, or finally, in the contention

period. If an adapter attempts to transmit while the

trunk is bus y its next transmit time is adjusted to its

=_cheduling period time (.priority delay). If an adapter

attempts "o transmit during the schedulin g period one

of two pos=_.ibil ities exist: 1) it att• ,,npt = to transmit

atter fixed delay but before i is pr i o- i ty del ay event

and 2) it attempts to transmit after its priority delay

event but before the , nd delay e:;ent. In the first

case, the adapter,is allowed `o transmit at It

a2

M^

IN

priority delay event and in the second ca =_e, the

adapter is forced to wait until ics end delay event is

signalled. This is in accordance with NSU s trunk.

access protocol. An adapter attempting to transmit

during the contention period is allowed to 0o =_.o

provided that the trunk is sensed idle. Once the

adapter has gained access. to a trunk thrclugh the trunk

accessprotocol as modeled, it will proceed to send its

message sequence.

In Figure 4.1, a complete message -with-data

sequence is shown. Appropriate timing and program flags

!M1 throuqh 116) are indicated. the algorithm shown in

Figure 4.2, in flow diagram form, illustrates the

overall activities of the simulation program. Using

these two figures a basic description of the program

+low may be performed. The first three blocks in Figure

4.2 perform initialization of program va^iables,

def i n i t i on of the ne twor l, con+ i our, .at i on , and prints a

description of the network to th_ auxiliary file Auxout

maintained bi the program. since trunk acce=_s has been

grantee (.previously described) an adapter w111 attempt

to send transmis=_.ion frames and data frame=_.. Program

flags are used to indicate where in the

message-with-data sequence the pre =_ent tran=_.mittino

adapter is located. The various update blocks !Case

through Case 7) update timing, bit counts, arid flag=..

b3

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Figure 4.2 Flow Diagram of Simulation

1.

Activity.

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65

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rea

^1p rea

UPI at*Ilse#

care IT set flag n1

No

rle`e.upe.taea#e :et fie M7

flee "a

Uplat#

N2 1CaaeSet fin MJClear lt4

No

FlaTe# [clplate

Mt e#eet fin Ft6

^ ear M^

D

Figure 4.2 Continued.

66

1

C19 'I

Pi

.IOF. POu-

n

NA

""ateCe]e SSet II. N7clear I1^

r Mo

Ten fUpde,e.. Care 6

set fle 116' Clear H^

He

UQI.t. I

Ceie ICie.r N6

,1 ^1 )]t M•ilirnn]+^Il Tln ♦Current

I /Tl^a Mo^--•{ r s e Q C

e+c

Te.

Itlnl Netvorl1 Itlnt [n'Sr.tl.11c. - tietirltr'slAl"Su+...rT

Figure 4.2 Continued.

67

I ^

ti

1

Cas?2 incorporates the adapter reservation scheme I(Figure 2.9). If a receiving adapter can be reserved

for the transmitt;nq adapter the message sequence

transmission will continue, otherwise, the adapter will

return to case2 each pass. throuci h the loop, until it^i reserves its receiver or aborts its tran=_mis=_ion. The

I

message proper from? is updated in c^se4. A messagei

length of 64 bytes is assumed for convenience. Ca.se5

updates the tran_.mission segment in which a data block:

is sent. In case6, determination of whether or not

another data sequence need =_. to be sent (based on the

attached device's buffer size) is made. If anothe7 data

block is required, then the period of time t'— t" will

be repeated, this will continue as required. In case',

updates to me =_=age delay (th •: time difference between

initial transmission time and the final trarsmission

time), trunk sequence transmission tally, and adapter

next transmission time are performed. The transmitting

and r e c e i v i n q adapter'_ are released for• ether

transmissions in case? also. The simulation will

continue until the user defined maximum time or the

maximum number of me=-sage sequences is exceeded. The

simulation will then print output statistic =_. to an

interactive terminal and an output file.

68

f

I 4.4.2 Model Set-Up

Figure 4.3 illustrate=. the basic set-up of the

network con+Iguration which the simulation program

operates on. All configurations to be modeled should be

set up accord in? to this diagram. In the ca c_e of a

single trunk configuration, adapters I through N are

used.

The =_.imulation (SiMIi u_es. this model

con+iguration to properl y identify and c=haracterize the

network adapter's, their attached devices, and data

sources.

4.5 System Files

There are three tiles associated vjIth the

simulation: program, Dfile, and Auxout files. The

program file (5im1) may be maintained as either c_ource

or object code since normal operation of the program

requires no changes to the program file. The files

Dfile and Au;<out a.re maintained ac standard ASCII text

files. Dfile cone:ins. a description of the network, and

is used by the program file for parameter values.

Auxout contains a text description of the network and

is used to store output statistics from a particular

program execution.

At the beginning of a program execution, an

interactive query allovls the user to use the network

configuration defined in the Dfile or define a new

69

• .'y^''' "rte. ^.. ^ . 4

c

^v

Ev^

uc

n_

L^L

n

v

0.z.

7

La

7

Cs,

Ki

r01► `^ ate. ?. ^^

t

i

77

1

con+iguration, which is then placed in this f le. The

auxi 1 iar y file Auxout, .s a. print formatted fi le and

may be directed to a printer for a hard cop y of a

program execution's statistics. Additionally, Auxout is

totally maintained by the pr on , art: file and thus ie.

transparent to the user until a print out of a

=_imuIation run is desired.

4.6 Reported Statistics

The network statistics, as comp i 1-d by the model,

are such that the y al lo,., the computation of measure=_

which indicate network performance. These measures are

defined as follows:

• D: The delay that occurs from the timean adapter becomes ready to transmita message sequence u.itil it actuallycompletes its transmission.

• S: The throughput of the local network;reported as the total rate of datatransmitted over the network.

• U: The utilization of the network; thisis given as normalized throughput.

o 0: Offered load; the total rate of datapresented to the network.

^there pos s ible the =_tatis t ic5 necessary to calculate

these measures will be reported for the entire ne t!-jork ,

the individual trunks, and the individual a.daptera.

I

!I

11

1•r

.61717''

4.7 Validation Criteria

Wh i le every attempt has !7een made to make th i s

simulation as close to the real =s=tem as possible,

software implementation of an electrc,nic s y stem has its

limitations. This simulation effort has been aimed

primarily at modeling the various protocols implemented

b! a HYPERchannel netkmork. It has been shown that these

protocols are the factor=_ ha -)ing the most impact on

s y stem performance I PAH841 , CWATS80I , [GOr&,09I , aid so

on. Therefor e, the simulation ,jas designed to model

ithese parameters as closel y as po^zsib, l The validit•r

o+ this model rests on a cle,r under_tandina of the

operation of HYPERchannel networks and the relationship

of this operation on s ystem performance.

Finally, it v) as not Peas i ble or practical t

establish a validation te s t bed at HO IIC. This due

1 arge 1 to the requ i remen is p l aced on the f ac i l i t y and

Its stated mi_ston. Thus , the model -),1 idAtion was done

emp r cal1y, based on knowledge of tide HfPEPchanneI

= y stem and the components attached at HOSC.

72t

0)9^77.­.W

Chap ter 5Model Analysis and Conclusions

In this chapter some of the theoretical consider-

-it i on i nk)ol v i ng H'YPERchanne 1 n twork performancet

measures will be developed. The results of exercisi nc.

the model in various configurations (based on the HOSC

esystem and components) will be presented. Finally, the

conclusion section, will attempt to describe the

results and their relation to operatinf, condi t i onE atf

t

H O'S C.

5.1 Theoretical Performance Bounds

In Chapter 4, se ,, erai stat,stirs .-jere discussed as

ti being important ; ndicators of network performance.

These were i den ti+ied as S, U, and D. S defined as

r throughput, is the rate of data f 1 ow or, the network. U

€P

or utilization, is normalized through p ut, this being

Ithe +rac`.ion of network cacao ty being u t i 1 ized, and

finall y , D or delay, i s the dela y between the time an

adapter re q uests the trunk and the t-me at which it

completes a transm =lion. In order +or the e-eper mental

,),lues to ha f)e meaning, some theoretical determination

of these stati st cs i s needed so that com p ar i son= may

t be made. In order to determine theoreticall y theset

vaiuea the network factors which most affect HSLN

performance mus t be V.noimn . The +ac for s .jh i c a++e -- t

tt^F.v

?3 I

1

this performance. i)dependent o+ the a, r ta,ched equipment

• Bandwidth• Propagation del ay• Number of bi ts per frame• Local network protocol• Offered load• Number of stations ESTALLS41

he + i r s t three of these t:.c t or letermine ?.

p?r?.meter ?., +rom 1 ,1hich th? netl.,iork utilization U. and

t hroJghput S ma ., be - jet?rmin ed.

Sin '_a a lo.:al area net.,,,,ork __ d. atinqu ehe^ +rom

I ono h au l n twork s and mu 1 t i pr .oce=_ _or =- -s tems b y the

bandwidth E, and distance =_ r.d, ink.)ol - ?d. The oroduct

1j-f the aw tt.,o term= ' E • d.; c an oe 1J =_?d to ch ..r ac ter i ze

the r.?t!-.jork. The tr?n5mi 3=1 on I?n,:jth :)r the med i Um m a^

be Ll e term! nedb^ di !idin^ this q u ?.ntIt'/ b:• the

pro p a gation - ,e Ioci ti '); of the m?dium. Thi s quant t.,

m?- be caicul •.ted a= f011-:)W

Tr?nam az1on Lengtn = g

Net-ork, System '=nrpr,r?.tio n =_U G^est= _ ?iu? .'f

-^u :er : e n t o+ the .peed f 1 ght be u _ed ror

pr opa g ati7n e1C.:,t. when attemotinci t.o e =_t?bI h

n._ t imorv. per4orm.n,:-^, Us n 4 th e a l Je o+ TO Me g a,.b i t? p er

=_.cond + or E. _ssum ng d to b? 1400 ?t, ?nd a=ink a

• 1

t -al ue of 1 .2 x 108 meter s/ sec for prop_agat i on ,e 1 o c i ty,

t ^ the theorc-t!cal transmission length of a 1000 foot

HYPERchannel network; is 127 bits.r

' The ratio of transmission bit length, to the

length of a typical frame (L) is the dimensionles_

quantity a. Thus,

a = tran=_mi s_ i on 1 ength of trunk,tyoir_.aI frame length bi*._,

or

a = BdVL

Since d/V is the wor=t ca se propagation time ;n

the medium it may be replaced with the H',`PERchannei

Fixeo Dela y . Pecall Ong from Chapter 4 that Fixed Deli/

may be calculated as

Fixed Dela y = 4 nsec f ,trunk length) + 2.i!8 uses,

the parameter a may be calculated as

a = B F,xed Delay?L

Thu =_ for a HYr^E-:RchannPI trunk of 1^ngth 1iii10 feet,

a is determined to be 0.0109. Typical values of a for a

HSU,I range from 0.01 to ot;e^ 1 . Hn intui tive discussion

of the mean i ng0 of the parameter a i s found i n Wi 1 1 i .am

c;tal 1 i n a ' s Lo cal Ne twor le. s. Th i s par ~me ter i s u d to

75

.1

1!

M

provide :,n upper bound on the utilization o+ the

netojork., Stallings also points out that this h;:pothesis

appears to be supported by experimental evidence; a

Part o+ t h i di_ ,_ussion +olicws:

....Consider a perfectly e++ic1ent accessmechanism that allows on!y one transmissionat a tine. As soon as one transmission isover, another node begins transmuting.Furthermore, the tran =_mission is puredata--no o-)erhe-ad bi ts.... 1;jhat i s themaximum possible utiiization o+ the network -'It can `:e expressed as the ratio o+ totalthroughput of the system }o the rapacit y orbandwidth:

U = throughputB

Li(Prcpagat i on + tran=_m i ss D n time;B

Li ( D/Q + L/B)B

+ a

So, utilization varies inversely v)ith a[STALL84].

Table 5.1 shows an example u_ i ng a to predict thQ

theoretical bo .-jnds on a network simil -Ar to the sy_.tem

at HCiSC. Un+ortunatel y , this method does not accc)unt

fDr the access protocol o+ the network:. Furthermore. it

assumes that the maximum propagation time i ncurred

on each transmission and that or, l one transmission ma,,

occur at a t i me. Despite these _h•_rtcomings, upper

76

. ^ UIP

:o

1 Theoretical Bounds on a HYpERchanne\Trunk of Length 1000 Feet.

Fixed Dela y = 6.08 usec

Bit Length = 127.0325 bits

a = 0.O1O9

U = \ = O.9892' =

S = ^ ° B = c, !-Ib/t sec

For an arbitrarr period cf t/me, t, the total bits

transferred ar*:

Total Bits =S*t

for t = 40 seconds

Total Bits = 1978 Megabits

1

lr

bounds on throughput and utilization may be calculated

using these techniques.

Another derivation o+ utilization which takes into

conside-atlon the effects of the protocol on the

network performance , ba y ed on the wr)rV of Robert

Metcalfe and Da"id Boggs IMETC763 is considered. Their

work is based on the Ethernet system which is a local

area network: operating under a CSMA/CD medium access

protocol with c=haracteristics similar to HYPERchannel.

;assume that there are N active nodes on the

^t•twor!: , ?ach ha-.) i ng l den t i cal data generating

, `g arazteristics. Furthermore, of ter a stat i on has

transmit t ed its packet, another station becomes ready

to transmit i t s packet , so that N a i so represents the

total offered 1 oad on tree network. Stal i l ng= i n h i s

amplification of CMETC763 n 0 t e S that time on th?

network ma ybe dI ,.)lded ; n t o t"uo component=_:

transmission internal (t;me required to transmit a

complete packet over the medium, , and a contention

nter,)aI (sequence of slots U)i t a colt ision or no

transml s it on; . Throu gin pu t then , becomes the rat i o cif

time tran =_mittino to the total time.

Recall that a ma y be written a

A = propagation timet r an sm l s =_ i on t i me

,j

t

t

IM

where the propagat i on t ime i s the worst case val lie of

time to transmit a frame o ,.er the medium, and

i transmission time is the time required to get a

complete frame onto the medium. If transmission time is

normalized to one, then a becomes propagation time. The

m n imum 1 ength of the tr ansmi ss i on sl of must be chosen

to al 1 ovi for the detes=t i on of a col 1 i s on and i s. equal

to twic? the end-to-end propagation time (1/2a) .

Following 'St al1inq's approach for the development

of the equations describing throughput and utilization,

the average 1 ength o* the con ter, t i ors i n ter-)al i

!e term ined b y first computing A, the probability that

exactly one station attempt :. transmission in a slot

an,^ acquires access to t'?^ nedl um. This is the bincmi.al

probability that any one stator, attempts to tr:.nsmi*

:.nd the others do not,

1

1 I

= t•d p( 1 - p, N - 1

ieih i c i s the probab 1 i tv that the de= i red oo_currence

acquisition Df the trunk) wi11 occur ir, N independent

triais. Since maximum throughput and utilization are

the quantities cf interest, maximizing A ,dill require

that p = i.'N so that,

7i

11

r4 = C 1 - 1/N.,N - 1

The estimated mean length of contention interval,

!rj, in slots i s.

i

..r

i Fr[ i =lots in row with :k col l i si oni=1 or no transmission followed by a

slot with no transm ssion]

o.

i=1

x

1.,jhich con-.: erges to,

E[!^i) I .H

The max imun ,al ue o+ utilization may now be

determined, vjhich is the length o+ a transmis_.ion

n ter-,, al as a proportion o f a cic r ^ c o n s i s.t i nqa of a

stransm i _sion and a contention interval

IJ = transmis_ on ti.nej total time

= tr:.nsm i s i on t ernetrar=_m i ssion time + contention time

= 1 _l + :a 1 - A

H

:; 1 r

^l

,t

n

For the 10 0 0 +oot HYPERchanne 1 ne tk..1C, r k prev i ousl v

described, assuming N = 4, U = U.971 and S is 48.55

Megabi t=_. per =_econd vwh i c corresponas n i cel y 1wi t the

results obtained using onl:r a < Tab le 5.1?.

The calculation of the parameter D or me=_sage

delay is not so ob-.ious. It appears empirically, that D

increases. without bound as the network approache

saturation. Hs the number of nodes increases, ac do the

number o+ acc;-ss reque=_ t the number of col l i s i on=_ ,

the number o+ retransmissions and also the time dela y a

node e y.per,ences before access is obtained, =_o D, Does

appear to i ncrease •Ni thout bound.

5.2 Presentation of Simulation Results

The Dre -iiou s =_ection pre =e ^ ta d analytical

techn iques u =_e+uI for Rred;cting the peak., or upper

1 imi is o+ a. HYPERchannel network c p erformance. Wh i i e

thy_ i_ useful for pred;ctinq top end performance, it

doe= not provide any usetul nformation about a

particuIar con +igurat ion o+ the networV.

The purpose o+ thi =_ simu1a.tion effort is to

prow i de the engi neers :.nd sc i en t i s s at Hii;C: 1wi t a

so+tware tool •)h i =h w1 1 1 prov i de i nformat i on on ne tl,,,ork

F rrformanc ai n a va.r i e t o+ con+ i qurat i on . Th i s

section presents results from this model for the

ne twork de=_.cr i p t i ons shown i n F i qure, 5. 1 and 5.4.

Detailed descriptions o+ these con+igurat+ons, along

SI

t

„

W

with simulation results are given in section 5.2.1 and

i the resu 1 is for a dual trunk. cant i gust ion are qi ven in

section 5.2.2.

5.2.1 Single Trunk HOSC Results.

The single trunk configuration, as shoe,,in in Figure

5. 1 , and de+ tried in terms of the model in Hppendi x 11J,

,:t)a = con s idered. Table 5.3 contain= a listing o+ the

rel a.t ive probabi 1 i ties th.a.t R Q ,en tran_mi t t e r :ji 1 1

-attempt to transmit to a of ven rece i l)er . This is used

by the =.imulation to establish the virtual Connection

be tw., -n de-) ices for commun i cat ; on . I n order to gauge

the performance o+ this con+ i qurat on over a !,a de r a.nge

of input loading, the topology o+ the net s;_fork a

defined was kept constant. The uttered 10?.d to the

network was ;cried b InCreasing the data source

generation rates to the de-) i ce s_ shown.i

Table 5.2 illustrates 'he method for computing

s y stem ner+ormance measures from simulation st_atisti_s

Tables 5.4 and 5.5, contain data points cal_ul.a`ed from

=1mu1•atlon runs, with each data point r'ep^esentlrig a

simulation run. These data points 1.vere plotted as s_h-_i,un

n F i aur- es 5. 2* and 5.

82

.s

11

r

w,

NI

Table 5.2 Cal cula.tion o+ Par=.meter=_ usinq_

Simulation Statistics.

S (throughput) = Tot I Bi is Trari=_mi ttedSimulation Time

U (utilization) =

Bari dvii dth

bi t°5G Mbit= per second

D ( dela y ) = Hv g. Message Dela y De l.- ce 1+ Avg. Message Delay De-)ice

+ as. Ay-a. Message Delay Device nn

The above expression for delay is used in the case1,,here tranami t t i ng dev I ces. ha-)e f i n i to Avera g e Mess-ageDelays. For the case where a transmuting Deviceattempt to transmit messa ges but ha an AverageMessage Dela y equal to zero (Average Message Dela y = ^^,:.rid Abort count > 0) it is assumed, that Me =_aqe Delay,or Delay, for the Network exceeded simulation time.

Offered Load is compiled by the simulation andoutput as one o+ i t_ statistics.

11

Y^

1

V '1

1

Table 5.3 Relative Probabilities for Transmitter/Rece i -:,er Pair= for Fi qijre 5. 1 .

Tran =_.mit ter/ Receiver Probability

111-311 0.7

111-321 0.3

211-4 1 1 .1)

221-421 1.0

11-211 0.01

33 11 221 U.01

321-211 0.01

321-221 0.01

331-421 1.0

34

a1

O

O '

uo OJ

o

ti

v1

Y

:J

^ df

u-.

v

:C..r

Ls.

•CCC y ^ ^ ,

P.m

I

1

1'c •O •

< K

85

. Dil

't

1

`'

OF FL

Table 5.4 Data Point= tar Figure 5.2

s +

R

4

5Plbxtes/sec

UMbytes

.0008092 . Ci00 1 2 1 5 . 0 234998

.0024680 .6003949 .0470083

.0040020 .000x403 0'0`2`,

.00671901 .1010751 . 1 1 21 1 40

.0142275 .0022764 .2242640

.029095o .0046553 .4486710

.0431299 .0069008 .1^7^341 0

.0586719 .00'3875 .8984520

. 0 7S`0 755 . 0 1 1 t•921 1. 12245A0

.1421105 .0227377 2.2420000

.118972 .0?.9036 4.4840000320 281 3 . 0 51 2450 .6 . 72'9n it n5137168 .11821946 9.969123110.5548880 .0887821 11.2103000.93-0150 .149624 22.-1200000

1.5409865 .2465578 44.84010002.3634718 .3781550 67.26030002.3250275 .3720044 89.68000003. 4732500 .5557200 224.20000003.6444500 .5831120 448.400000114.5387500 .7261400 672.60000004.60'3c. 250 .7373800 896.80000004.6521500 .74450 30 1 1 21 . OIDi1 CIO i111

4.7345000 .7575000 2242.00000004._510500 .6962640 4:40.00000004.8016750 .7682680 67_0.00000004.8004000 .76x,0640 8968.0CI000004.70 ?8500 .7676560 11210.0000000

Average C-= e '_ _

.0021383Ci01 :;,50ij001 78330016166

.0015533

.0016850

.0016283001`11600185830042466

.38757660u.54 7500042916

140>40J ,4 ii

.4622500140>40>40140>40

4 r^> 4 C,

>40>40>40

66

^Aa li

aJ

N

L

tilization versus Offered Load:)r Single 'Trunk Simulation.

39

t1

- sue' _ - , . ^'•^

., r

Offered Load (Log Bits)

WEIR C=)I

T?ble 5.5 Data Points for Figure 5.3.

Control BitsMbits

.1005832` . 3076200P .4885992

.67209121 .7754192

1 .635,49603.3552900

{ 5.09739206.83254-08.424640016.438120027. 1 1 o8800

43. 003472 002.547020074.7621600

134.9088000204.0576000

i347.8608000353.9296000539.07681300685. 70 860 13 0

1 562.904800050..03200013564. 3<;^20000543. 6464000624.7024000527.836200052c' . 1 13 6 0 C, 052'S.7168001)

Data Bitsrib is

.177536520456.854160

1.1634161.3745812.9146165.960952'? . 71 '^3c011.9770401 4.9°976028.992240-ill . 690 1 OU58.011760

1 I) 1 .8.,,400C,102.3072001 ,t^4 . 616000289.070400408.488000390.079200572.364800480.5176008o9. 3-116000910 . 7220 013924.616000971 .3920013767. 82480 1'11008.6900001 1)08. 0080001006.6000013

13 BitsMb is

.1879984

.3760664

.5642040

.7210600

.89691201.79411203.58'?36805.3867230

. 1 3751 603.'i79r,0ii017.93o000035.872000053.837500071.753840089.5824000

179.3600000358.7208000538.13624000717.440,01)IDfj

1 7G^ . 6011111111111

D'587.20111)0005380.801300007174.4000000g9-t„x.000[100017936.000000034729.00000005 )..1)3.0000013071744.000000089686.0000000

R8

`t1

E 0

1

v y

71

inC J kr

4> f

Qb 7 i^ 11Offered Load (Loe bits)

(a) : n

a,O

n

n

0

J1

V CJQ

•r.

r

J J :4

Offered Load (Lor bits)

(b)

Figure 5.3 Plot of Transmitted Control and Data Bitsversus Offered Load for Single Trunk Simulation.

39

t1

e

A

w W) W u) w u) co u)o• m a^ r f` n ^D n

( s7 ^8 80^)

s7^g a^a^ Fa>>^wsua.^^,

.-1

1

.-1

Wf9 t) T k) m U) D ul r9^+ m rm r- r- W

Tq

D n n

( S1 ^l)

sl{q jolluo:) paa7Twsuull

Nu-4

m

00O

^.1

brovr-a

b

4I)w'LO

C^ O

•r1

L

N ^u E-4 •4f'0 to

M ^

U G^ rp 4.d H-

C 11^-4

to-4 Go •-+4 fnLc 4v oV w

b

a.) OU ,..3.4E -JN yG 4r1 'U4 WH 'LO

'LO N

L Nv 4-4 va >

v4

00-4w

,4 NL.4

c]T

0

brov

r-

m4v

D w'LO

tin

90

1

♦r 1

1

1

The system configuration and data flow rates

indicated in figure 5.1 are a typical loading of the

main trunk of the HOSC system. The total offered

load (G) for the system as depicted in figure 5.1 is

computed as follows (G the offered load is the total

number of data bits offered to the channel):

DEVICE DATA ARP, I kIAL RATE

lil 15 Kbytes/sec = 120 kbps

211 4 Kbytes/sec = 32 kbps

221 6.4 Kbytes/sec = 51.2 kbps

311 1 Kbytes/sec = 8 kbps

321 1 kb y tes/sec = 8 kbps

331 .625 Kbytes/sec = 5 kbps

411 0

421 0

431 0

IN

TOTAL OFFERED LOA` = 224.2 kbps.

In a 40 second period a total of 8.976 Mbits or

6.953 (Loci bits) would be offered for transmission

across the HYPERchannel's network. Referring to

figure 5,2 the utilization of the HYPERchannel trunk

for this offered load is approximately 2;:. The

throughput rate is thus (.02) * (50 Mbits per

second) = 1 Mbps. Obviously the system is nowhere

91

Q41

near its upper limit in data throughput rate, trunk

utilization and hence not in offered load.

The approximate number of total bits

transmitted to send a 2 kb y te block of data ma y be

estimated from figure 2.8 using Table 2.2 as a

reference. From figure 2.8 it is apparent that 7

transmission frame format f i el ds, 9 response frame

fields, and 2 response frames with data format

fields are transmitted to accomplish t`:e

transmission of 2 kby tes of data. This amounts to

an absolute minimum transmission of 1900 bits total

for 15000 bits of data or absolute minimum overhead

of 22.5%. For longer data blocks the overhead is a

smaller percentage and ma y be calculated b y the

relationship (assuming no collisions):

ABSOLUTE MINIMUM TOTAL BITS SENT

PER 2 KBYTES OF DATA = 19500 + (N-1)18500

where N = the number of 2 kbytes of

data.

The educt i or, in transmission ok^erhead for

mul*-^;e transmission of data segements

of 2 kbytes of data is not si gn i f i cant in number, of

bits transmitted but the timing and number of times

the channel is free for contention is r?duced by a

significant amount. It will be obser , )ed from the

92

rf

I ^

F

sue" •- -

--4.

simulation rune. that an average overhead of 50Y for

low offered load and 100% for high offered load is

the case. This overhead increase is due to the

non—intege multiples of 2 kbytes of data to be sent

and to collisions.

Figure 5.3 depicts the average delay and number

of collisions versus offered 1oad. The average

delay is an aggregate delay number and a 1.-roe delay

is indicative that at least one device is

experiencing a large dela y , Thus it ma y ir- =;te

that onl y one dev i ce i s unab l - to t- ansmi t but all

the remainin g ^r _es may be transmitting

satisfactorily. However it is an indicator that

things are begining to sour on the overall network

performance.

Likewise the number of collisions is an

aggregate sum and indicates the relative number of

retry transmission attempts the s y stem is

experiencing. Since the HYPERchannel is not a pure

contention s y stem (such as ETHERNET) the increase of

collisions does not necessarily indicate

accompan y ing data loss or absolute inability of an

adapter to communicate. Again it is an indicator

that thing= are riot so well on the overall netvvcrk.

93

t1

r

117- qW-^.

v ^^•

OW

From the results of figure 5.3 it is apparent

' that as the offered load increases past about I.5

(31.62 Mbits for 40 seconds or 790 kbits per second)

the system is beginning to experience traffic

congestion. The system's trunk utilization, figure

5.2, is seen to start a rise at this point (7.5) of

of(vOd ioad and it may be observed that at an

offered load of about 9.5 (3162 Mbits for 40 seconds.

or 79 Mbits per second) the trunk utilization is

entering saturation. At this point it is safe to

sa y that some devices are gust not able to transmit

all their data. Somewhere in between these two

offered loads is a point that would do well to be

identified as the maximum useful offered lord

condition. Using the rule of thumt for normal

maximum operating offered load for pure contention

systems (ETHERNET is an example of a pure

contention system) the maximum operating offered

load would be set to approximately 1/2e or 13.35% of

the channel bandwidth. For slotted contention

systems this rule of thumb figure is approximately

1/e or 36.7%. The H'r'PERchanneI i s a hybrid

priority/contention system with prioritized time

slottinq and it is reasonable to ex p ect to load the

system to the 36.7% trunk utilization. Inspecting

94

1

the graph of trunk ut i 1 i zat i on versos offered load,

figure 5.21 , it Is observed that the offered load for

a utilization figure of 36.7% is approximately 8.5

(log bits) or a 7.9 Mbps aggregrate rate (316 Mbits

in a 40 second).

Inspection of the graphs for the transmitted

control bits and the transmitted data bits versus

offered load, figure 5.3, also illustrate that at

8.5 offered load the control bits and data bit

curves start to enter saturation. Thus it is

reasonable to state that the maximum operating

offe^ed load (in pure aggregrate rate data bits)

should be 8.5. This is an aggregrate rate of

offered data of 7.9 Mbps or 15.8% of the channel

bandwidth of 50 Mbits. Remember that an absolute

minimum of 22.5% overhead i needed at low collision

rates and thus 7.9 Mbps of offered data plus 2?.5%

overhead is approximately 9.6775 Mbps or, 19.35% of

the channel bandwidth. (This assumes all data

blocks are inteqral 2 Kbytes in size).

A further comment of the figure 5.3c and 5.3 d

is in order. The offered data to the channel, G,

:see Table 5.5) is only the actual data to be

transmitted. The actual number of data and control

bits required (as evidenced from the simulation

95

J

11M

tM

t

i

runs), which when added together equal the channel

throughput S, will not equal G but be greater thani

G.

It should be observed that for low offered load

the actual transmitted bits on the channel amounts

to 2.54 times the offered load and at high offered

load this figure decreases to about 2 times the

offered load until saturation tales place. This

apparent increase in efficiency is mi sleaoing since

the prioritize' time slotting mode of operation

replaces the contention portion of the channel

algorithm and stagnation of the throughput (U*B)

takes place.

Thus the 7.9 Mbps offered aggregate load

corresponds to about 16 Mbps to 18 Mbps actual1

channel offered total load or 36% of the channel

bandwidth.

FROM THIS DISCUSSION AND THE SIMULATION

RESULTS COUPLED WITH THE ANALYTICAL RESULTS

IT IS RECOMMENDED THAT THE TOTAL AGGREGr'iTE

OFFERED DATA TO THE HYPERchannel SHOULD BE

HELD TO 8 Mbps OR LESS. IN FACT DUE TO THE

UNCERTAINT'( OF ESTIMATING AGGREGATE DATA RATES

A MAXIMUM OF 4 Mbps WOULD SEEM PRUDENT.

96

I5.2.2 Dual Trunk HOSC Results

The dual trunk configuration as shown in

Figure 5.4 and detailed in Appendix V, was

considered. Once again, the relative probabilities

for transmitter/

receiver pairs in this configuration are contained

in Table 5.6. In order to compare the effect of the

dual trunk configuration with the )reuious results,

the configuration of trunk 2 1n Figure 5.4 was

defined as the n-::ile trunk confiouration

previously considered. The topology of this

configuration was held constant and the offered

load var i ed, the resulting data points are

contained in Tables 5.7, 5. 80, and 5.9. These data

points were plotted as shown in Figures 5.5, 5.6,

and 5.7.

In a secenario that has been ,fudged to be a

normal environment for the HOSC dual trunk system,

the transmissions from trunk 1 to trunk 2 have

aggregate data rate of 10 kbytes/sec. The device

on trunk 1 alwa ys transmitts acros s_. the trunks to

trunk 2. The cross traffic from trunk 2 to trunk 1

has a lower data rate and a lower, probabi11ty of

request for transmission. Thus the majority of

9%

1

04f,

Table 5..5 Relative Probabilities for Transmitter/Peceiver Pairs +or Figure 5.4.

Transmitter/Receiver

1 1 1 -521

211-411

211-421

311-531

321-521

321-111

411-311

411-321

421-311

421-321

431-521

Probability

1.0

0.7

0.

1.0

1.3

0.3

0.01

0.01

0.01

0.01

1.0

98

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99

TaL^le 5.% Data Point =_ for Figure 5.5 (Trunk 1)

S U r, A-)erage DMb y tes/sec Mbytes_ secs

.00017973 .000028758 .0155758 .0006650

.00065895 .000105433 .04.573.30 .0018928

.00116560 .000186500 .0760532 .0018800

.00161704 .000258726 .109071) .0015842

.00239248 .0003827p7 .1521:90 .11014942

.00711533 .001138454 .4564050 .0013442

.011$9340 .001'025'40 .76:0820 .0013142

.01665555 .0026a4880 1.0658o00 .00,3000

.02376770 .003802830 1.5233900 .00110111)

.07053307 .J112852921 4.5644800 .0013228

.11621025 .018593600 7.0050000 .0064371

.16076790 .025722800 10.649o000 .0014928

.2256948,:) . 0361 1 1 1 1 1 15. 21 1 60011 , 111167786

.60678250 .0970352011 45.6?00000 .0288557

.01607500 .146572000 76 A50Jn00 .1i'j773001.1720'750 .187532400 106.4700000 401.50 327750 .240524400 1 52 . 1 1) 1) O u 0 1:1 . 712555772.52247200 .403590000 45c,.310130000 )-1.02.93269750 .4^-923100 7-.0.5000000 >403.15442500 .504700000 1064.7000000 ?403.4350000 .5 4960000 1377.0000000 >403.49356500 .558970000 4563.0000000 >40:-.5247!250 .503960-400 7605,1301-10000 >40

3.54453500 .567125000 10647.0000000 40

100

1^

U

Table 5.8 Data Points +or Figure 5.5 (Trunk 2).

SH bytes:,sec

.00017973

.00142330

.00204550

.00321635

.00478900

.01557770

.02o4142603715009.05333650.10056900.16651150.32703950.34178971. 865532t50

2.4?4515001.384273722.05963550L.24 087f(1.889152401.9243-114401.939254002.314184202.387359752.40758250

U

.000028758

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.000327280

.00051461t

.000766240

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. 13 2"664180 005232o322.05468o000.138485200.399122400. 221 48=;800.329541600.519?74CI iii.302200000.30789';,OO CI

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106.4700000152.100000045.,- 3000001)760 .501]0001]

1 i1 o4 . 70000C,01 37,1 . 0 ID 0 ID 0 0 114563. i)Qpljljiiil

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101

t1

C

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0

Offered Load (Log bits) Trunk 1

(a)

E-iS

., •, if

.•

c ►^o

2

^ 1

6 ie 11

Offered Load (Log bits) Trunk 2

(b)

Figure 5.5 Plot of Utilization versus Offered Loadfor Dual Trunk Simulation.

102

1

OF K-

J

^r

? 1M 11

Offered Load (log bits)

(c)

n IEA

O ^^

y 1 ~^^

•. ;

o ^

:J s.

r ^^ 1 ^_^ 1J V 1

Offered Load (log bits)

(d)

Figure 5.5 Plot of utilization versus Offered Load

for Dual Trunk Simulation.

103 I ^

1

Table 5.9 Data Points for Figure=_. 5.6 and 5.7.

Trunk 1 Trunk 2Control Data Control Data 13

Mbits Mbits Mbits Mhits Mbits

.?27870 .026112 .327870 .026112 .1-2460

. 12021 9 .095744 .229786 .2,6680 .37386

.207651 165366 .339076 .315528 .60842

.29508:? 2350JI=- .52c096 ._;

. -,26231 .339456 .761 1 90 .771480 1 .21 3951.2677o8 i.009064 2.416856 2.569176 3.o51242.120224 1.688576 4.083456 4.375576 o.i!88o52,972682 2.36748E 5.728200 6.1727c0 8. 526884.24045o 3.377152 8.220800 8.873680 12.18712

12.568..'20 10.009600 24.681128 26.717520 X6.5158420.699520 16.4853611 44.027040 9.256640 60.8400028.644880 22.813200 59.468240 45. 20520 x:5.1968040.207760 32.0220011 93.209000 1o.174320 121 .6980108.088000 36.082400 193.222400 33.748000 ;c,5.0,100C113.210400 129.933o00 411.237o1]0 38.700720 008.40000208.792000 16o.272800 440.801000 2.10599:: 851.70000274.172000 206.876800 631.889600 27.193'50 121o.80000449.335200 357.85o000 396.320000 142.42,8000 3650.40000522.411200 4 16.052000 607.6 4 9 6'1 1] .032768 60 4.00000

5cc1 .91 ,980 1 0 447. 499200 61 5.,t,8 0 60 C', .1 1 0 206 =51 7 . c,01100595.59( 600 474. 32480 0 520 . 44480 0 . 1 1 0-188 1 1 C; 1 13 00 ii 0

X 0.745600 457.195200 717.39:3600 2_.145360 36504.0ID111-C16. 3.976000 453.948000 733.2008001 30.' 14320 It. 0840.O;ii1j1]1j_•7^.87 .^ i100 454.3752 111! 732.42081101 38.0015c.40 S517b.0U00i1

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4k)

the cross trunk transmissions occur from trunk 1 to

trunk 2. This is envisioned as the worst case

condition for cross trunk traffic since the

destination trunk is the busiest trunk.

Looking at the curves from figures 5.5, 5.6

and 5." it may be obBerved that for trunk 1 the

operational parameters under increasing offered

load are very similar to that for the single trunk

secenario, the exception being the lowered trunk

utilization before saturation is encountered.

Aga iii the maximum offerea load operationg point is

seen to occur for about 3.5 offered load and hence

as before the trunk 1 aggregate offered load should

be held to 8 Mbps or less.

The situation is not as good for trunk 2. The

cras s_ trunk traffic ham p ers the normal traffic flow

for trunk 2 and it is apparent from the simulation

curves that the maximum aggregate offered data load

should be held to less than 8 or 2.5 Mbps. This is

considerably less than that for the singie trunk

simulation and clearly demonstrates the effect of

heavy cross trunk communication requirements.

Froin figure 3.4 the aggregate offered data

load of the two trunks may be calculated. This

107

1

1'

was judged to represent a t ypical operating load

for the dual trunk HOSC system.

DEVICE DATA ARRIVAL RATE

111 10 Kbytes/sec = 80 kbps

TRUNK 1 TOTAL OFFERED LOAD = 80 kbps

211 15 kbytesisec = 120 kbps

311 4 Kbytes/sec 32 kbps

321 6.4 kbytes/sec = 51.2 kbps

411 1 Kbytes/sec = 8 kbps

421 1 Kbytes/sec = 8 kbpsIN

431 1 kbytes,"sec = 8 kbps

511 0

52: 0

531 0

TRUNK 2 TOTAL OFFERED 'OAD = 224.2 kbps.

The aggregate offered data load for trunk 1 is

80 kbps (6.505 log bits) and for trunk 2 is 224.2

kbps (6.952 log bits). These offered aggregate

data rates are less than the desired maximum by a

cons der abl a amount and room for gr-?wth ex i sts.

There is an allowable factor of 100 for trunk 1 and

an allowable factor of 10 for trunk 2 growth rates.

Keeping in mind that this aggregate data load for

108 t

EN I14 ASSIGNING

THEY ARE MOST

r

1

4^

trunk 2 is the same as for the single trunk

simulation configuration of figure 5.1 it is

easily ;discerned that the cross trunk traffic whileI

amounting to a 35% increase in trunk 2 traffic

lowers the maximum operating offered load

potential o7 trunk 2 by a factor of almost 4 (down

from 8 Mbps to 2.5 Mbps). Furthermore the curve of

figure 5.5 illustrates that the utilization of

trunk 1 saturates at 55% as opposed to the 75%

point for the single trunk case.

FOP, DUAL CONFIGURATIONS IT SHOULD BE NOTED

THAT THE MAXIMUM AGGREGATE OPERATING LOAD

POTENTIAL OF THE TRUNKS IS LOWERED BY A

CONSIDERABLE AMOUNT. THIS ARISES FROM THE

NECESSITY OF DUAL RESERVATION OF BOTH TRUNK

ADAPTERS. THE CROSS TRUNK TRAFFIC LOWERS

THE MAXIMUM OPERATING UTILIZATION POTENTIAL

70 APPROXIMATELY 75% OF THAT FOR THE SINGLE

TRUNK.

5.3 Analysis and Conclusions

The goal of this work was to develop a =.of tware

tool, with partic=ular emphasis on NSC`s HYPERchannel

network, to aid the engineers and scientists at the

HOSC, to perform s ystem analysis. This study began with

a description of the HYPERchannel and the various

protocols implemented by the network. The relationship

of these protocols to s ystem performance was discussed.

The s ystem components which make up the HOSC were

exam i ned, these components are examined for information

ipurposes, in that the attributes of these devices were

used to define the test configurations presented in

section 5.2. The configurations chosen for testing by

the simulation, are oased on the system shown in Figure

3.1. The results of this testing a. • e presented inr

section 5.2 of this work.

The data, which appear in Section 5.2, are plottedm^

in all cases versus the Log (base 10) of offered load,

where offered 1 -Dad i s ex. pres=_.ed i n b ts. So that x

offered load of 7 on any plot i s the i nk. , erse Log ( base

10 ) of 7 a)h i c i q u a I to 1 x 107 b i t=_ . I n F i Qure i

(5.2 and 5.5) utilization is plotted versus offered

load. Utilization is a dimen- onless figure ranging

from U to 1. In Figures (5.3, 5.6, and 5.7) the Lc.,g

(.base 10) of transmitted control and data bits are

plotted versus offered load. As before a value of 7 on

110

11

the offered load axis represents 1 x 10 7 bit=_, Whether

this is data or control bits, is indicated on the axis

of its respective plot. Finally, the simulation time

used, 40 seconds, was the same for all simulation runs.

The results obtained from the =_.in91e trunk

configuration of the model are found in Figures 5.2 and

5.3. The results as plotted in Figure 5.2 and tabulated

in Table 5.3, compare fa-.orably with results obtained

by other researchers [FRAN82], [FRAN64], and [WATS801.

While nu:nerical results differ due to different

topologies bung modeled, overall performance of the

network is essentially the same. The overall

pe^formance of th i s netwoi, k, and that reported

elsewhere, appear: to approach some relatively constant

I eve 1 (saturation) as offered load increa_es. A

slightly different presentation of these results are

plotted in Figure 5.3 and tabulated in Table 5.5. This -.

data. is presented as transmitted control and data. bits

versus offered load. These plots re-present the actual

amount of data and control bi is being transmuted oy

the network versus offered load. Control bits are these

bits trxn =_mitted by an adapter to perform )etwork

functions and are consilered overhead loadin g . Data

bits transmitted, are those bits offered to the network

b y attached dev i ces for• transfer over the n twork .

Offered load represents the total amount of data

111 1

U. I

u

presented to the nets.,jork for transmission over the

network. Thus, as offered load increases, the amount of

data bits transmitted should increase. Since network

services are requested, network functions increase,

thereby increasing the amount :)f network messages

relating to these functions. This will c;u=e a

corresponding increase in the amount of control bits

being transmitted over the networK. The plots in Figure

5.3, both exhibit nearly linear properties until a

certain point coffered load approximately equal to '>>

is reached, after which the data and control bits

transmitted remain nearly constant.

An offered load of 9 on these plots, represents an

aggregate offered load of 3.:25 Mb y tas/sec beinU

presented to the neti:jork for transmission. This is

equ i val en t to an off ne twork source reo 1_est i ng ne tvjorL,

services every 0.04 usec. According to puhiished

1.0

f i gures C FRAH823 , ( FRAM84] , and [ I.!ATS82] , an adap ter

requesting *he trunk, transmitting its data, and then

releasing itself and its receiving adapter will re.1uire

A minimum of 840 usec to send one message-with-data

sequence containing one 2 Kby te data block. If the off

network sources' data rates are such that net•A)orh.

services are requested faster than the network can

process these requests, then data loss will occur. At

this point the network is en ter irng saturation. Thi=s. is

112 1

cJ

reflected in the plots of data bits transmitted versus

offered load. After uf+ered lead exceeds the point

where offered load is approximately S', any further

increase in the offered load does not produce a

corr-sponding increase in the amount of data and

control bits transmitted. This indicates that the

network is saturated and can not transmit an ,/ greater

amount o+ data or control bits.

The normal offered load to the network, based on

observations of the s y stem described in Chapter 3, and

de ta. i 1 ed in Appendix I'), appear s_ to be approximately

6.95 (Offered Load). This figure results from summation

o+ the data rates applied to the network, multiplied by

simulation time, and then performing a Log -"ba.Le 10''

operat or on the resu l t . Thus t I =_ rye ti.,ork i s,

according to simulation results, operating below its

potential b y a factor of approximately 100. This_

indicates that e>, pansion o+ this configuration would be

pos_.ibl? t o some extent.

In order to exam i ne the effects f a second trunk

added to a network , the con+ i gur.at i D pi shown in F i cur e

5.4, and detailed in Appendix V, 1.Nas modeled, This

configuration is simiIar to the single trunk

con+iguration in that the topology o+ trunk 2 (Figure

5.4) 1 s the same as that shown in Figure 5.1. In order

to ob=.er-)e the e++ec is on trunk 2) due to another trunk

113

-4i

7 '.ems+ = y

having access to it, the probability of a transmi=_sion

to trunk 2 from trunk 1 ,ras set higher than the

probability o+ the re-)erne operation. It should be

apparent, that a dual trunk network in which each trunk

hRs need of onl y sporadic use of the other, would have

noticeably better performance than the con+ guration

presented in this work. The results of modelino this

configuration are plotted in Figures 5.5 through 5.7,

and are tabulated in Tables 5.' through 5.-;.

Examination of these re su 1 t.s shows that trunk 1 i s

reIati 1e Iy unaffected, althou gh utilization is lower.

Utilization in this case is approximately constant at a

val ue of 0 .55 for i ncreas i ng off=_ red l oad. Th i s f i Qure

is approximatel y 25% less than the comparable value for

a =_ i nol e trunk ne ti..)ork , th ; s i s due 1 arise 1 y to the

topology of the network . On trunk 1 there are t"..)o

adapters, which communicate exclusively with each

other. There i s a 1 arger number of adapters c,n trunK 2;

which affec t = the common adapter to both trunk., in

that, multi-trunk operation is =lower. This slownes s of

the multi -trunk operation ma y be attributed to the

common adapter hav i rig to compete for a bus i er trunk to

complete its' tran=_mission. 7 h ,js, the common adapter

will be reserved for longer periods of time, directly

a+fec ` Ina throughput, and conse q uentl y utilization, on

both trunk =_. Performance on trunk 1 of th i s topology,

114

t

1^ r

. _ 1

R

c^

with the exception of lower utilization, is rougrily the

same a ,a that of a single trunk network, as expected.

However, the results fo r, trunk 2 are drastically

reduced from that of a single trunk configuration. An

Examination of Figures 5.2 and 5.5. show that

ut i 1 ization of the trunk. is ve r y nearly the aa,me for an

offered load of approximately 5 to a load of eery

near 1 y S. Af ter an offered 1 oad of 8 i s reached, the

dual trunk con+ i gurat i on' s u t i l i zat ion i s dr as i c a i l y

reduced. In Figure 5.6, the con ,:rol and data. bits

trar.smi tted ovar trunk I are plotted. These curvss

exhibit behavior similar to that of the single trunk

model discussed pre , )iousl y . This is not the c.?.se for

the control and data bits transmitted over trunk 2

(Figure 5.7). Both of these plots exhibit linear

beha-) i or to a certain extent, but while the control

bits transmitted are anti slightli affe,_t-d, the

transmitted data is drasticalI x altered at the same

point that utilization breaks doi.in . Based an the

description of this retwork contained ir, append V.

the normal o+fered load is approximatel y 7.08. ms shown

in the plotted da t a, t his- topology ha.s ver:: limited

r?nice in regard to offered load, which makes it

vu i nerabl e to perforrr,_.,.._a degr 3dat i on due to 1 oad

variation.

1

115

t

i'l,

Thus, : single trunk s ystem exhibits greater

potential for expansion than the dual trunk topology

modeled. Rather than allow a dual trunk system of this

nature, it would be better (Performance related) to

place the additional device seeking communication 1.Aiith 1i

another trunk , at a h i gh rate , ph;/si cal 1 y on the trunk

it re q uests the most.

The val i di t of t i s simul at i on i s based c,n the

understandino of the s y stem and the structure of the

model . Whi l e it 1Ajould be better to ?stabl ish g al idi t;•

by comparison with actual configurations and their

measured performance, the feasibility of establishing a

test bed for this purpose is remote, due largel y to the

intensive mission requ rements at the HOSC.

Finally, the author be i eoes that the stated

resew,- ch Qoa 1 -7 have been reache(3. Howe ,.)er, in thi

model, as in all things there is considerable room for

impro-.)ement. Future expansion of the model might be

made, to includ? intra-adapter mes_age trnsfers, and

more than one adapter to more than one trunk. This.

i-jould ser-)e to lend more accurac y and sophistication to

`he present model. The current model appears to p,:)s=e=_.=_

reasonable accuracy and vAl i di ty, wi th the stated

conditions under which it was developed.

116

I ,

04 J

APPENDIX I

Sott^,^are Source Listing

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APPENDIX IISummary of ISO-O SI Model of Distributed Network=_

Layer

Definition

1. Physical Concerned with tran=_.mis=_.ion ofunstructured bit stream o k . , er physicallink; involves such ;.arameters assignal voltage swing and bit duration;deals with the mechanical, electrical,and procedureal characteristics toestablish, maintain, and deactivate thephysical link. (RS-232-C, RS-449, X.29)

2. Data Link Converts an unreliable transmissionchannel into a reliable one; sendsblocks of data (frame--.) w ; th checksum;uses error• detection and frameaknowledgement (HDLG, SOLO, BiSync)

3. Network Transmits packets of data through anetwork; packets may be independent(datagram) or tra ,)erse a preestablishednetwork connection (virtual circuit);responsible for routing and congestioncontrol. (X.25, layer 3)

4. Transport Provides reliable, transparent transfero+ data between end point=_.; providesend-to-end error recover y and flowcontrol

5. Session Provides means of establishing,manaoing, and terminating connection(session) between two processes; mayprovide checkpoint and restart service,quaran t i ne ser y i c?

6. Presentation Pe , +orms generally use+ul transform-ations on data to provide a standard-ized application interface and toprovide common communications services;i.e., encr yption, text compression,reformatting

7. Application P rovides services. to the users of GSIenvironment; i.e.. t ransaction ser,)er,file tra rl_.fer protocol, ne tl;jorkmanagement

T h i s. =_urrimary taken from, Local Networks, AnIntroduction, b y 1.0i l l i am Sta.l l ings (STr LL84] .

168

t

V..

U APPENDIX IIISimulation Software Module Descriptions

1. Simi.

Simi is the top level procedure of the simulation

program. It controls simulation activity and flow in

the simulation environment. Referring to Figure 4.2,

the first *hree blocks perform v ariable initialization,

define the simulation network configuration, and prints

a description of the network in the auxiliary file

Auxout. The loop indicated is the actual simulation

activit y (described in subsequent sections). Simi ,.► ill

print compiled overall network statistics to the system

default output device and to the auxiliar yfile Auxout,

b y invoking Printstats. The procedure Activitysummary

prints a breakdown of the network statistics b ydevice,i

to the auxiliary file (Auxout).

2. Initialize

Thi=_ procedure is used to initialize certain

global variables which need to be spec if i ed for each

executi o') of the program. Table III.1, is a. listing of

the interactive queries posed by thi s_ procedure, along

with an yconstraints in-^olved. The remainino variables

which do not re-auire user-intervention are also

initialized in this section.

169

t1

4

r

Table III.1 Interactive Queries Posed by INITIALIZE

Quern: Is there more than one Trunk ? Y:es or N)oResponse:

Y or N, if answered yes then theflag Trunks is set true, otherwise,Trunks is Set false.

Example: YVariable: Trunks = True

Query: Identification heading for run:Response: Valid re sp on ses. a.re alphanumeric string

with length less than 50 characters.Heading appears on each output page.

Example: Simulation Configuration TestVariabl y : Heading

Query: Maximum run time in secondsResponse: Valid re =.p onse=_. are real positive numbers

which represent the time a simulation runwill execute

Example: 40Variable: Max time

Quer y : Maximum Successful Sequence Transmissions ?Response: Valid responses are rea l pu_iti-^e numbers

i,Aih i (:h represent the number of sur_cr-ssf1.0message-with-data sequences will be

F transferred over the enure networksimulation ends l.kihen Maxseqtx or Maxtimeis exceeded

Example: 1 ii0oii0Variable: Max=,egtx

r

Query: Seed for Random Number GeneratorResponse: Integer number. For best results, the

number specified should be an odd,positive number with :.t least 5 digitsand not divisible by 5 or 7.

Ex am p le: 16227Variable: U

The following queries will be posed if Trunks is True.

i^Query: Was the last Run a Single Trunk

Configure.tion Y)es or N)oResponse: Y or N, if answered yes, Inputmode =

interacti -je, thus forcing redefinition ofthe network. If answered no then the

` tolIov.iirig query, will be posed.` Example: Y

170

t

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i`V'

Variable: Inputmode

Query: Input Mode: I)nteractive or F)ile ?

Response: This query will be posed only ifthe 1 as t run k,,ias a dual trunkconfiguration, this is indicated byanswering no to the above queryIf answered F, the network configurationused will be read out of the Dfile. Ifanswered I, then the network will havebe redefined t: y the user

Example: FVariable Inputmode

The following queries will be posed if Trunk=. = False

Quer y : Was the last run a Dual Trunk configurationY)es o,- N)o

Response: As before, yes will 'orce redefinitionof the network and no vji 1 1 cause thenext quer y to be posed.

Example: Nt)a.r i abl n : Inputmode

Quer y : Input Mode: I)nteractive or F)ile ?Response: A before, answering no to the above

quer y will allow this quer y to be posed.The effect of this quer y is the same asabove

Ex amp I IVariable: Inputmode

171 1

,01111111

3. CharacterizeNetwork

Procedure ._haracterizeNetwork eata.bl rshe: the

experimental framework of the simirlation. The

individual adapters, devices, and sources are defined.

There are titlo +ays tc establ i sh an exuer imental mcode r ,

interactively, or trom an auxi 1 iary fi le (N i ) E). The

method employed is de!ermined b ythe t.al,,? %)f

Inputmc1jr, defined b yprocedure Initialize. if

Inputmode is equal to interactive, then the System

description will he Nrovided b y the user interactively.

A sub-procedure P,ewriteDfile w i I i be called to store

this interactive system description in the Dfile. If

Inputmode equals +ile, then the system description used

is the one stored in the auxiliary file (Dfile),

implying at prev i ous run where Dfile was created

interactively. A detai led I istinq of the ir,ter:active

queries posed 'b y Char ac ter izeNetwork is presented in

Table III.2.

4. PrintnetCescription

The p- ,tee o-i th i s procec;ure i s to pr i n It a

detailed descr,,-itior, of the system being modeled in the

auxiliary file Auxout.

5. FiadNext(Tmitter)

As prev iou=_.ly stated this model is a discrete

event simulation. The event which drives the simulation

is an Zdapter's next scheduled transmit time. The

1'2

tM

AT-

►.. ,:,rte ^ , x

Table II1.2 Queries Posed by CHARACTI-RIZENETWORK

Query: Length of Trunks in feet (used for enddelay)Trunk 1:Trunk 2: ( appears for dual trunk )

Response: Fl o s,iti real numberVa g r a.bl e : Trunk 1 ength [ 1 ]

Query: Number of Adapters in Network:Response: Integer number in range 1 to Maxrnumad.antensVar i abl e : Numotada.p ters

I n the Dual Trunk catse the followino query will be made

Query: Which Adapter is Common to both Trunks ? •Response Integer n,imber in range 1 to MaxnumadapterVariable: Comm--d

Query: Adapter #i: Distance in ft. from priority 1adapter otr Trunk 1

Response: Positive real numbersVariable: Ada p ter[ i l .distfromF;l

Query: Adapter Priority: Give .n integerform,i.e., n = 1,2,....

Response: Pos i t i v p i nteger numbersVariable: Adapterp[il.Pl F

Query: Adapter Retry Count: This must be a uniquenumber for each adapter, in the range 0-64 4

Response: Positive integer numbersVariable: A.daD`erp(il.retryct

The following two queries are made for the commonadapter two both trunks

Query: Distance ire ft. from priority 1 adapter onTrunk 2

Response: Posi t i ,:ie real numbers')ariahle: Adapter[Commadl.DisttrtAl

Query: Adapter Priority: Give in integerform,i.e., n = 1,2,.....

Response: Positive real numbersVariable: Adapter[Commadl.P2

Query: Adapter[il.Device[jl desc.lptionDevice status (Open or Closed)

ReeEponse: 0 c C. C if Ada ,,i ter, [iI Device[jIhas an active, network ae ,:) ice con-

171

1

Wi

J w. 1I'

nected to it. 0 otherwise.Variable: Adapter[il.DeviceCj].Open

Query: Device ID (<= 24 Char)Response: Alphanumeric =trinqVariable: Adapter[i].Device(il .Id

Query: Device to Adapter I/O rate (Bytes/sec)Response: Positive real number representinq the speed

of the de k.) i ce I/O port.k ariable: Adapter[i].DeviceCjl.tferra.to

Quer y : Number of Uata Sources in Device(j]:Response: Integer number representin gi the number o+

data sources supplying the device with dataVariable: Adapter( i]. Devi -_e[ .jl Numo+sources

Quer y : Data Source(k) ID:Response: Al ph anuineri string with length 214

haractersVariable: Adapter[i].De-,ice[j].Source[k].Id

Query: SourceCk] Data gen rate (Bytes/sec)Response: Real number, representing the rate at

which data arrives at device.Variable: Hdap ter Ci7. De l) iceC.jI Source( VI.Genrate

Query: Buffer size in bytesResponse: Integer number, size of buffer filled in

device before network transmission isrequested.

Variable: Adapter[il.Device[j].,:_,^_.-_i^[k.].E;uf+ersize

Query: Receiver Id code ? (0 to end list)Response-3 digit inte ger number, representing

Adapter#,Device#,and Source#Variable: Adapter[ iI Device( j].SourceCk:].Id

Query: Probability ?Respon=_.e: Positive real number to < number 1

representing the reIative probabilitythat the Rbo ,.,e rece i ver lyji 1 1 be tran

k mitted to b y thisadap ter Ii].deviceIj].sojrceCkI

Variable: Adap ter IiI Device[iI Source IkI Prob

I {

II

174

1

4

Il

procedure FinoNext scans all ad ,+pters. and picks the one

with the smallest next time to t r ansmit, compared to

(Currenttime) =_. emulation time. After selecting one

adapter, it will then determine if thi s_ adapter is

reserved for a. reception of a messa ge sequence from

another adapter. If the adapter is reserved, then it is

forced to wait, if not reserved then it is returned to

the main program as the current transmitter.

6. PickA(Tmitter;

Th i s procedure i s used to p i ck a ^ece i ver for a

transmitting adapter. The current transmitter's

at,^ibutes are passed to thi s_. procedure, and an

aop^opriate receiver is selected based on its list of

possible receivers and the relative probability of the

adapter being a receiver for the transmitter, . This

procedure also determines whether a transmitter is

attempting to transmit to a different trunk. If

:kt tempt enq .a dual trunk communication, the trans_.mitter

is assigned an intermediate receiver which is common to

both trunks.

7. ACollision

The purpose of the boolean function Ai=olli s_.ion, i

to determine whether or not the current transmitter has

unre s_.tricted use of the simulated transmi s_.sic-i medium.

If another device attempts to transmit djring a time

period of equal to, or,less than , twice the

175

1

I - — .

119,

bi

W.

propagation time between the two, a collision condition

will be declared. Thus. ACollision scans the network

devices comparing their next transmit time to the

current transmitter's next transmit time and determines

whether or not a collision has occurred. In dual trunk

simulations the function ACollision will scan vhich

ever trunk is being used by the current transmitter. If

a collision is declared, then collision statistics are

updated, and both the current transmitter s and

colliding adapter's next transmission times are

updated.

8. Uniform

The Uniform procedure functions as a Random Humber

Generator. It genera r e- oseudo —random numbers in the

range u < number < 1. This procedure is used in various

sections of the simulation in order to inject some

randomness in the selection of receivers and in )ar>inQ

some time parameters.

9. Update

Update is the procedure in +,v)h i ch the bulk of the

iYPERchannel protocol is modeled. As pre ,.^iously stated,

the simulation is. driver, by a. discrete e k.-ent. This type

of simulation is often referred to as activity

scanning, or event scanning. The event which drives the

simulation is a transmit request b' e an adapter. Each

device is assumed to possess certain attribute=_.

176

t

t;^i

bl

31

determined from obserna*ion=_ of the real system. As an

example of this. if a device receives data from aniii

off-net source to transmit over the network at an

average rate of 15 Kilob y tes per second, and stores

• this data in a r:byte buffer, i t wi 11 request a

network transmission every 0.1365 seconds. This then

serve=_. to generate transmission requests for the

simulation and in turn, bec=omes the event which drives

ithe simulation clock.

This procedure consists of seven cases, each of

which updates the current transmitter according to

where it is in a mess-ge-with-data sequence

transmission. The time periods involved are illustrated

in Figure 4.1, where the individual cases are indicated

and the program flags that signal the case an adapter

will go to on a transmit request.

iCaael: The first time an adapter signals a request

to transmit there wi 1 1 be no message f l a.gs ac t i ve ,

indicating the beginning of a message sequence. Case

air i 1 1 be invoked and the adapter wi 1 1 reserve i tse 1 f,

initialize dela yto 1 usec and retry to zero

(reservation scheme), set M1 true, and adjust its next

t me to transmit by 64 uses.

Case2: This case incorporates the adapter

reservation scheme (Figure 2.9). An adapter entering

(Case2, Lase3, Cas.e4, Cases, Case6, or Case') is first

177

4

. 6J,)

checked to see if i t is involved in a col 1 i si on wi th

I other devices. If no collision is detected the adapter

is checked for dual trunk communication, if it is, then

an intermediate destination is determined. If not, then

the adapter's intended receiver is checked to see if it

i s reserved by another adapter. If the intended

receiver is not re ser-.:, ed, then the receiving Adapter-

,,,j i 11 be set reser ,:)ed. Appropriate adjustments to the

various Iran=_m i s__ i on times, bit counts, message flags,

and trunk parameters are made. If, however, the

}

intended receiver is al ready res.ervr-d, the tr ansmi t t i ng

adapter o.i' iII enter the retry-delay re=ervation schemet

and -ts message flag will not be changed. Thus, the

ada p ter will -1-urn t,_, Case!. °each time selected until

it reserves a receiver, or ;kborts it s tran=_•mission. If

a. col 1 i s i on is detected when ._ n ter i ng 'Case2, Case 3,

Ca_•e4, Cas-e5, Case 6, or Ca=_.e7) then , appropr i ate

adjustments to adapter and trunk ,iming is made.

Case?: Th i s case deal s u.)i th the message proper.

portior of the message sequence. If no collision i•s

detected, adjustments are made to the adapter And trunk

parameters.

Ca-e4: This case is essentially the same as Cas.e3,

with the exception o+ the values used to update adapter

. and trunk parameters.

lib

W—

IM

.1

Cases: In Case5 a determination of how man y data

c-equences need to be transmitted is made, this based on

the size of the data buffer of the transmitting source.

The first sequence will be updated and if more than one

equence i to be sent then message flag l •14 will not be

chanced. App; .^,,r i ate t i m i n adjustment =_ anti made i r.

this section also.

Case6: When all data sequences have been sent,

Case6 i s invoked. Appropriate timing adjustments are

made in this section.

Case7: There are three pos=_ibiIities encounte^ed

in this section: same trunk communication, adapter to

common trunk adapter communication, and c=ommon trunk

adapter to adapter communication. T h ? last t';Jo in

cimbination c.mpri_.e a dual trunk communication. In all

cases this is the termination of a message sequence.

Both, the receiver and tran=_.mitter are released, and

appropriate timing adjustments are made.

10 Printstats

Thi s pro ce dure compi les and writes. to `he system

deta.uIt output device, and auxiliary file (Auxo 1jt), an

overall summary of network activity. Examples of this

fE fol 1 ow:

179 \

Sinqle Trunk Simulation Results

*** End of Run 1`le twork Statistics ***

Current Time : nn.nnnn secs

Successful Sequence Transmissions :nnnnn

Collisions (Frames) :nnnnnMaiis (Frames) :n.nE+nn

Total Attempts (Sequences) :nnnnnTotal Aborts :nnnnn

Total Trunk Act; ,je Time :nn.nnnn secs

Total Active Time :nn.nnn f.

Control Bytes Transmitted :n.nnnnnE+nn Mbytes

Data Bytes Transmitted :n.nnnnnE+nn MbytesTotal Bytes Transmitted :n.nnnnnE+nn t1bytes_

Total Offered Load :n.nnnnnE+nn Mbytes

M

Dual Trunk Simulation Results

*** End of Run Network Statistic=#*Current Time : nn.nnnn secs

Successful Sequence Transmissions

Successful Sequence Transmissions—Trunk. 1SuccessfuI Sequence T ranSmis- icns—Trunk 2Collisions (Fr.•.mes)Waits (I+ Frames)Total Attempts (Sequences)Total Abort=_.Attempted Trunk —Trunk TransmissionsSuccessful Trunk—Trunk Trans.mis=_ion=

Trunk 1 Active TimeTrunk 2 Active TimeTotal Trunk Active Time

Trunk I Ac t i ,)e TimeTrunk 2 Active TimeTotal Trunk Active Time

:nnnnn:nnnnnr nnnn:nnnnn:n.nE+nri:nnnnn:nnnnn:nnnnnnr,n ',n:n.nnnn secs:n.nnnn secs:n.nnnn secs:nnnnnn is:nn.nnn:nn.nnn %

Control B y tes Transmitted Trunk 1 :n.nn Mb y te=-

Data Bytes Transmitted Trunk I :n.nn Mbytea

Control Bytes Transmitted Trunk. 2 :n.nn MbytesData Byte= Transmitted Trunk 2 :n.nn Mbytes_

Total Bytes Transmitted :n .nn M bytes

Total Offered Load :n.rn Mbytes

180

I1. Activity Sumnary

Th i s procedure prints. de to i led t)reakdown by

device, of network activities. This summary is printed

to the system de+ai.jl t output de l.) i ce, and the aux i 1 i ary

file (Auxcut). The categories detailed are as follows:

Time Active: Time device spent trans-mitting and receiving.

Time Waiting: Time de l) ice spent waitingto transmit due to itsadapter t,eing reserved.

Time inCollision=_.: Time involved in collisions

b y de l i ce .

Average MessageDelay: This is the average time

length of a messagesequence sent by thisdevice. If this number is0, either the de k);ce can`ttransmit, or it tried tobut never sent an entiremessage sequence. In thelatter ca=_.e, mes =_.aq_e delaywould have to be > thansimulated run time.

Abort count: Number of aborted tran=_.mis-_.ion attempts (reservationscheme).

Transmissionfount: Plumber of succe s sful 1

transmitted sequences

Reception Count: Number of successfullyreceived sequences

Wait Count: Number of times. devicehad to wait to transmit

OD

181

1

V

Collision Count: plumber of times engaciedin a collision. (note:these numbers are actuallydoubt e the total shown i noverall statistics due toone count for each col -

I lidinq adapter.

of

W'

M;

182

._...`^.. -- — -- ----^--•c- ,,mac: • -.,., .

- .. . 1

APPENDIX IV

T ypical Single Trunk Simulation Results

183 11

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k

APPENDIX V

T ypical Dual Trunk Simulation Results

190t

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REFERENCES AND BIBLIOGRAPHY

DE080 Digital Equipment Corporation, VAX HardwareHandbook. Ma ynard, Ma: 1981.

DEC31 Digital Equipment Corporation, VAXArchitecture. f-Ikynard, Ma: 1981

DEC82 Digital Equipment Corporation, VAX SoftwareHandbook, Maynard, Ma:l'r31-1982.

D0NN79 Donnelly, J. E., and Yeh, J. W. "Interactionbetween Protocol Levels. in a Prioritized CEMABroadcast Net,.,jork." Computer Networks,March 79

FRAN80 Franta, W. R., and Bilodeau, M. B. "Analysisof a Prioritized CSMA Protocol Based onStaggered Delays." Acta Informatica,June, 1980.

FRAN82 Franta, W. R., and Heath, M. B. "Performanceof HYPERchannel Networks: Parameters, Measure-ments, Models, and Analysis " University ofMinnesota, Computer Science Department,Technical Report 82-3, January, 1982.

F.1;1AN84 Franta, W. R., and Heath, M. B. "Measurementand Analsis of HYPERchannel Networks.' IEEETransactions on Computers, March, 1984.

HEr182 He yman, D. P. "An Anal ysis of the Carrier-SenseMultiple Hccess Protocol." The bell SystemTechnical Journal, Vol.61, No.B, Oct., 1='132.

MAUL84 Mauldin, J. D. "A Software Model of theHYPERchannel Local Area Network at theHuntsville Operation Support Center." Thesissubmitted to Mississippi State University,Mississippi State, 11s. 198.1.

METC76 Metcalfe, R. M., and Bo+fs, D. R. "Ethernet:Packet Switching for Local Networks."Communications o+ the ACM, Jul y , 1976.

NHS• ,82 National Aeronautics and Space Administration.George C. 11arsnall Space Flight Center."Shuttle Program: HOST, Operations ProceduresDocument." SPMD 1.2.1, Revision 6, May, 1982.

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NSC79 Network Systems Corporation. A400 AdapterReference Manual, 42990008. Brookl yn Park,MN: 1979.

NSC80a Network S ystems Corporation. Nucle-is AdapterReference Manual, 4290003. Brookl yn Park,[IN: 1980.

NSC80b Network S ystems Corporation. H1rPERchanneISystems Description, A01--000002. BrooklynPark, MN: 1980.

NSC81 Network S ystem Corporation. PI 13/14Peripheral Interface Reference Manual,42990015. Brookl yn Park, MN: 1981.

PEC81 Perkin Elmer Corporation. "Model 324CIProcessors," Product Information Sheet. OceanPort, NJ: 1981.

STAL84 Stallings. W. Local Networks. New York:MacMillan Publishi ng Company, 1984.

WATS82 Watson. B. W. ")al i dat i on of a. Discrete E-)entComputer Model of Network Systems Corporation'sHYPERchannel". 7th Conference on LocalComputer Network =_. Minneapolis, t-1N: 15182.

YEH79 Yeh. J. W. "Simulations of Local ComputerNetworks". 4th Conference on Local ComputerNetworks. Minneapolis, MIA: 1979.

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