S1 Ch07 Technologies Review

The

Saig

on C

TT

Chapter 7 (Cont.)

Layer 2 - Technologies

The

Saig

on C

TT

Topic

1. Basics of Token Ring2. Basics of Fiber Distributed Data Interface (FDDI3. Ethernet and IEEE 802.34. Layer 2 Devices5. Effects of Layer 2 Devices on Data Flow6. Basic Ethernet 10BASE-T Troubleshooting7. Summary

The

Saig

on C

TT

History of Ethernet

• 1960’s– CSMA/CD developed at the University of Hawaii

• 1970’s– First experimental Ethernet system at Xerox

PARC• 1980’s

– IEEE 802.3 released– Digital Equipment, Intel, and Xerox jointly

develop & release Ethernet Version 2.0• DIX standard• Substantially compatible with IEEE 802.3

The

Saig

on C

TT

History of Ethernet

• Today, the term Ethernet is often used to refer to all Carrier Sense Multiple Access/Collision Detection (CSMA/CD) LAN’s that generally conform to Ethernet specifications, including IEEE 802.3.

The

Saig

on C

TT

CSMA/CD MAC• Stations can access the network at any time• Stations listen to the network before

transmitting and while transmitting• If no signal on the wire, the station sends• If two stations send at the same time, a

collision occurs– Both transmissions are damaged– Both stations must retransmit– Backoff algorithms determine when each station

can retransmit

The

Saig

on C

TT

Broadcast Networks• All stations see all transmissions• Each station must examine each frame to

determine if they are the destination– If yes, the frame is passed to upper layers for

processing• Ethernet & IEEE 802.3 are both broadcast

networks

The

Saig

on C

TT

Comparing Ethernet and IEEE 802.3

• Ethernet provides services to all of OSI Layer 1 & 2• IEEE 802.3 specifies the physical layer and the MAC

sub layer of the data link layer.– Does not define a Logical Link Control sublayer protocol

• Both are implemented through hardware, typically an NIC card

The

Saig

on C

TT

Ethernet Family Tree

Category 5 UTP100m802.3ab1000BaseTShielded copper25m802.3z1000BaseCxSingle-mode or multimode fiber3000m802.3z1000BaseLxMultimode fiber220-550m802.3z1000BaseSxSingle-mode fiber10,000m802.3u100BaseFxMultimode fiber400/2000 m802.3u100BaseFxCategory 3, 4, or 5 UTP100 m802.3u100BaseT2Category 3 UTP100 m 802.3u100BaseT4Category 5 UTP100 m802.3u100BaseTxFiber2000 m802.310BaseFLCategory 3, 4, or 5 UTP100 m802.310BaseT50-Ohm thin coaxial cable185 m802.310Base250-Ohm thick coaxial cable500m802.310Base5

Cable TypeMaximum Cable Length

MAC Sublayer

SpecificationStandard

The

Saig

on C

TT

Ethernet and IEEE 802.3 framingformat

Ethernet-II( DIX 2.0)

FCSDataTypeSource AddressDest. AddressPreamble

446-15002667+1

Start Frame

Delimiter

1

IEEE 802.3

FCS802.2

Header & Data

Length

Source Address

Dest. AddressPreamble

464-15002667

The

Saig

on C

TT

Preamble Field

• Preamble– Alternating patterns of 1s and 0s, ended by 2 bits 11– Tells receiving stations whether frame is Ethernet or

IEEE 802.3• Preamble + SOF(10101011) =Ethernet frame

Start Frame Delimiter

1

IEEE 802.3

FCS802.2 Header & Data

Length

Source Address


464-15002667

The

Saig

on C

TT

Start of Frame

Start

DelimiterFrame

1

IEEE 802.3


Length

Source Address


464-15002667

• Start of Frame– SOF– IEEE 802.3 only– Delimiter byte ends with 2 consecutive 1 bits

• Synchronize the frame-reception, ready to receive

– Explicitly specified in Ethernet

The

Saig

on C

TT

Address


1

IEEE 802.3


Length

Source Address


464-15002667

• Destination and source addresses– 1st 3 bytes are vendor-specific

• Specified by IEE– Last 3 bytes are specified by vendor

• Ethernet or IEEE 802.3 vendor– Source address is always unicast– Destination can be unicast, multicast, or broadcast

The

Saig

on C

TT

Type/Length


1

IEEE 802.3


Length

Source Address


464-15002667

• Type (Ethernetype)– Ethernet only– Specifies the upper-layer protocol to receive the data

• Length– IEEE 802.3 only– Number of bytes of data field

The

Saig

on C

TT

Data - EthernetEthernet-II( DIX 2.0)


446-15002667+1

• Data—Ethernet– At least 46 bytes of data– Padding bytes inserted as needed

The

Saig

on C

TT

Data IEEE 802.3


1

IEEE 802.3


Length

Source Address


464-15002667

• Data—IEEE 802.3– Upper-layer protocol destination is defined within the

data portion of the frame (DSAP, SSAP, Control)– At least 64 bytes– Padding bytes inserted as needed

The

Saig

on C

TT

FCSEthernet-II( DIX 2.0)


446-15002667+1

• Frame Check Sequence– 4 byte CRC value

The

Saig

on C

TT

Ethernet MAC

The

Saig

on C

TT

Ethernet MAC• Connectionless network architecture

– Source device is not notified of successful delivery of data packet

– “Best-effort” delivery system

The

Saig

on C

TT

Signaling• Most common varieties use Manchester

encoding• Newer, faster varieties use more complex

encoding schemes

The

Saig

on C

TT

Half Duplex Ethernet Design

• 10Base-T Transceivers– Built on to NIC– Use 4 wires– 1 pair transmits– 1 pair receives

The

Saig

on C

TT

10Base-T Media & Topologies

• Why 10Base-T?– Commonly installed– Basic configuration– Not always applicable

The

Saig

on C

TT

Star Topology

• Media runs from a central hub out to each device

• Central point of control• All communication is via the hub

The

Saig

on C

TT

Hubs• Receive data on one port, broadcast it to

all other ports• Active or passive

– Active• Connection and regeneration• Extends networking distances• Sometimes called concentrators

– Passive• Connection only

The

Saig

on C

TT

Advantages of star topology• Easy to design and install• Ease of maintenance

– Only area of concentration is at the hub– Layout is easy to modify and troubleshoot

• Easy to add workstations• Limited network effect if a device or cable

goes down– Increased reliability

The

Saig

on C

TT

Disadvantages of star topology• Lots of media needed

– Increases setup costs• Hub represents single point of failure

The

Saig

on C

TT

Horizontal Cabling (TIA/EIA 568A)

Work Station(Patch Cable)

HorizontalCable Run

Cross-Connect Jumpers(Patch Cable)

3m 90m 6m+ + = 99m

The

Saig

on C

TT

Network Area

• Cable length limitations limit the size of a star topology network

• Sneakernet outside the 200m x 200 area

The

Saig

on C

TT

Extending the network

• Repeaters regenerate and retime signals• Attenuation is “repaired”• Cable length specification “restarts”

The

Saig

on C

TT

Layer 2 Devices

• NICS• Bridge• Switch

The

Saig

on C

TT

NICs• Provides ports for network connection• Communicate with network via serial

connection• Communication with computer through

parallel connection• Resources required:

– IRQ, I/O address, …

The

Saig

on C

TT

Selection Factors for NICs

• Type of network– Ethernet, Token Ring, FDDI

• Type of media– Twisted pair, coax, fiber

• Type of system bus– PCI, ISA

The

Saig

on C

TT

NIC Operations• Layer 1 & Layer 2 device• Primarily Layer 2

– Communicates with upper layers in the computer• Logical Link Control (LLC)

– Has MAC address burned in– Encapsulates data into frames– Provides access to the media

• Also Layer 1– Creates signals and interfaces with the media– On-board transceiver

The

Saig

on C

TT

Effects of Layer 2 Devices• Two primary reasons for segmenting a

LAN:– Isolate traffic between segments– Achieve more bandwidth per user by

creating smaller collision domains• Use Bridge & Switch to solve

The

Saig

on C

TT

Bridges• Connects two network segments

– Can connect different layer 2 protocols• Ethernet, Token Ring, FDDI

• Makes intelligent decisions about traffic– Reduces unnecessary traffic– Minimizes collisions– Filters traffic based on MAC address

• Maintains address tables• Rarely implemented today

– Conceptually important

The

Saig

on C

TT

Address Table built

The

Saig

on C

TT

Bridge Operations• Broadcasts and multicast frames are forwarded

by a bridge cause Broadcast Storm• Transparent bridges perform switching of frames

using Layer 2 headers and Layer 2 logic and are Layer 3 protocol-independent.

• Store-and-forward switch method. Additional latency

• The transparent bridge must perform processing on the frame, which also can increase latency

Note Source-route bridging use by Token ring

The

Saig

on C

TT

Switching

The

Saig

on C

TT

Switching OperationMicro-segmentation

– Each switch port acts as a micro bridge (Layer 2 device)

– Multiple traffic paths within the switch–Virtual circuits–Temporarily exist - only when needed

– Each data frame has a dedicated path• No collisions• Increases bandwidth availability

–Each host gets full bandwidth

The

Saig

on C

TT

Advantages of Switches• Much faster than bridges

– Hardware based, not software– Switch method:

• Store-and-forward• Cut-through• FragmentFree

• Support new uses– e.g. virtual LANs

• Reduce collision domains

The

Saig

on C

TT

Advantages of Switches• Allows many users to communicate in parallel

– Creates virtual circuits– Creates dedicated segments

• Collision free • Maximizes bandwidth

• Cost effective– Can simply replace hubs in same cable

infrastructure• Minimal disruption

• Flexible network management– Software based configuration

The

Saig

on C

TT

Collision Domain

The

Saig

on C

TT

Broadcast Domains

The

Saig

on C

TT

Router• The Router is a layer 3 (Network) device,

but operates at layers 1-3.– Routers create the highest level of

segmentation because of their ability to make exact determinations of where to send the data packet.

– Because routers perform more functions than bridges, they operate with a higher rate of latency.

The

Saig

on C

TTIdentify Broadcast Domains andCollision Domains

The

Saig

on C

TT

Troubleshooting

The

Saig

on C

TT

Labs• 7.6.2 You will use the help menu, and the

process of experimentation, to learn the basics of navigating within the Network environment.

• 7.6.3 You will learn about the problems/symptoms that the NI program can detect.

• 7.6.4 Use Protocol Inspector software to examine some simple network utilization and frame statistics, in order to make more real the concept of frame flow as the heartbeat of the LAN

S1 Ch07 Technologies Review

Documents

Transcript of S1 Ch07 Technologies Review