Slide Jaringan Komunikasi

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Pengantar – Komunikasi Data (1)

TUJUAN• Berevolusi dan selalu berkembang sejak pertama kali adanya Computing

• Mempelajari konsep-konsep dasar dan terminologi yang berhubungan dengankomunikasi data dan jaringan komputer

• Mempelajari beberapa teknik yang dipergunakan untuk melakukan transfer data antara dua computer

e.g. dua komputer dalam satu ruangan atau dibedakan dengan jarak dan terhubungmelalui jaringan telepon

• Mempelajari bermacam-macam fungsi dan protokol jaringan berdasarkan referensidari ISO Reference Model

• Mempelajari dasar-dasar teori yang berhubungan dengan transmisi digital

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KOMUNIKASI DATA• Pertukaran data antara dua perangkat (komputer)• Terhubung melalui beberapa macam media transmisi

SISTEM KOMUNIKASI DATA• Kombinasi dari hardware dan software• Memungkinkan terjadinya pertukaran komunikasi data

KOMPONEN-KOMPONEN:

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Komponen - komponen sistem komunikasi data

• Pesan (Message):Informasi (data) yang akan dikirim

Dapat berupa teks, gambar, suara dll

• Pengirim/Penerima (Sender/Receiver):Perangkat untuk mengirim/menerima pesan data (data message)

Dapat berupa komputer, kamera video dll

Membuat istilah “end system atau host” yang mengacu pada keduanya

• Medium:Lintasan fisik di mana data/pesan bergerak dari pengirim menuju penerima

Dapat berupa kabel, gelombang radio dll


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Komponen - komponen sistem komunikasi data

• Protokol:Peraturan-peraturan yang mengatur komunikasi dataMenggambarkan kesepakatan antara perangkat-perangkat komunikasiTanpa protokol, dua perangkat mungkin mungkin untuk saling terhubung, tetapitidak saling berkomunikasi

Sebagai contoh adalah dua orang yang berbicara dengan bahasa yang berbeda, tidak dapat mengerti satu dengan yang lainnya

Hubungan antara perangkat - perangkat komunikasi• Konfigurasi sambungan:

Mendefinisikan bagaimana cara dua atau beberapa perangkat komunikasitersambung pada link

• Mode transmisi:Mendefinisikan arah alur sinyal antara dua perangkat yang terhubung


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2. Pengantar– Jaringan komunikasi data: Beberapa tipe dari jaringan komunikasi data– Standar-standar: Evolusi, Beberapa badan international

3. Pengantar– OSI model arsitektur: Lapisan dan stuktur model, Fungsi setiap lapisan

4. Komunikasi Data Interface– Media transmisi: Beberapa macam tipe fisik media transmisi yang dipergunakan

untuk data transmisi, Karakteristik dan limitasi dari setiap tipe– Tipe-tipe sinyal: Beberapa tipe sinyal yang digunakan dalam komunikasi data,

Sumber sinyal– Sumber redaman dan distorsi: Beberapa tipe redaman dan distorsi, pengaruh

redaman dan distorsi pada sinyal– Delay propagasi: Pengaruhnya pada sinyal– Standar interface lapisan fisik: Standar yang digunakan untuk menghubungkan

peralatan komunikasi

Materi Kuliah (1)

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5. Transmisi Data– Dasar transmisi data: Beberapa tipe mode transmisi

– Transmisi sinkron dan asinkron: Perbedaan dua tipe kontrol transmisi

– Teknik deteksi kesalahan

– Kompresi data: Beberapa tipe algoritma kompresi data

– Kendali transmisi: Perbedaan dua tipe kontrol transmisi

– Kendali komunikasi: Beberapa tipe perangkat komunikasi kendali

6. Dasar-dasar Protokol– Kendali kesalahan: pengertian-pengertian dasar dalam kendali kesalahan

– Idle RQ: prinsip kerja, arsitektur, spesifikasi, penggunaan

– Continuous RQ: prinsip kerja, arsitektur, penggunaan

– Manajemen Link

Materi Kuliah (2)

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7. Protocol TCP/IP– Karakteristik– Fungsi tiap lapisan

8. Data Link Control– Protokol character-oriented– Protokol bit-oriented– Standar interface lapisan kendali link

9. Multiplexing– FDM - Frequency-Division Multiplexing– Synchronous TDM (Time-Division Multiplexing)– Statistical TDM

10. Multiple Access– FDMA – Frequency Division Multiple Access– TDMA – Time Division Multiple Access– CDMA – Code Division Multiple Access– Random Access

Materi Kuliah (3)

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Point-to-point

• wire link

• other link: PSTN (Public Switched Telephone Network) & Modem

Jaringan Komunikasi Data (1)

A B

modemmodem

PSTN

A B

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LAN (Local Area (data) Network)

• More than 2 computers involved in an application

• A switched communication network facility used to enable all thecomputers to communicate with one another at different times

• If all the computers are distributed around single office/building, it is possible to install one single LAN

• Otherwise, a few LAN is connected through a link (site-wide (backbone) LAN)


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• More than 2 computers involved in an application


A

C

BLAN 1

LAN 3

LAN 2

Mainframe or minicomputer, advanced workstation or personal computer

Bridge

Technical and office automation

Site-wide (backbone) LAN

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Manufactoring automation

Manufactoring cells

Intracell LAN

Factorywide (backbone) LAN

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WAN (Wide Area (data) Network)• when computers are located in different establishments

(sites), and then used public carrier facilities• Different types depend on the nature of applications

e.g.:• Enterprisewide Private Network: when computers belong to the

same enterprise and having a requirement to transfer some amounts of data between sites by leasing transmission lines (circuits) from the public carriers and install a private switching system at each site

• PSDN – Public Switched Data Network: similar as above, where public carrier network is used

• ISDN – Integrated Services Digital Networks: similar, with ability to transmit data without modems


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• Enterprisewide Private Network:

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• PSDN:

PSDN

PSDN = Public Switched Data Network

TC = Terminal Controller

= Interface standards

= Communication subsystem (hardware and software)

computer

computercomputer

computer

TC

TC

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• ISDN:

ISDN

NTE

NTENTE

NTE

NTE = Network termination equipmentISDN = Integrated Services Digital Network

voice handset

computer

voice handset

computer

voice handset

computer

voice handset

computer

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Internetwork or Internet; where communication facility include multiple networks such as LAN-WAN-LAN

Broadband Multiservice Networks

• Connect workstations that support desktop video telephony, videoconferencing and more general multimedia services

• ‘Broadband’ means of its high transmission bit rates

ATM (Asynchronous Transfer Mode)

• An approach for transmission and switching within the networks

• Used to distinguish data communication & speech and video communication


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• Worldwide interwork:

Site-wideLAN

Site-wideLAN

NationalPSDN

NationalPSDN

Site-wideLAN

Site-wideLAN

Ground station

Satellite

Ground station

= Gateway

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MAN (Metropolitan Area Network)

• A new network with the interconnection of ATM LANs; and data-only LANs are distributed around a town or city


ATMWAN

ATMMAN

ATMMAN

ATMLAN

ATMLAN

Data-onlyLAN

Data-onlyLAN

Data-only workstation / server

Multimedia workstation / server

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Evolution:

• 1970s – Mainframe, PSTN

• 1980s – Network computing, separate data and voice networks

• 1990s – Personal computing, workstations, LAN, ISDN, Internet

• 2000s – Global integrated multimedia infomedia network

Provides a model for development

Allows a product to work regardless of the individual manufacturer

Developed by cooperation among standards organizations, e.g. ISO, ITU-T, IEEE, IETF

Standards (1)

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Documented agreements containing technical specifications

• To be used consistently as rules, guidelines, or definitions of characteristics of a system

• To ensure that adhered systems are fit for their purposes

Standards contribute to

• Making life simpler

• Open systems

• Ensure compatibility

• Bring costs down by encouraging competition

Most telecom related standards are international

Standards (2)

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Enhanced product quality and reliability

Simplification for improved usability

Increased distribution efficiency, and ease of maintenance

Ensure compatibility and interoperability

Encourage competition

• Bring costs down

• Ensure stable supply

Developed by cooperation among standards organizations, e.g. ISO, ITU-T, IEEE, IETF

Standards (3)

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ISO: International Standards Organization

• A worldwide federation of national standards bodies from some 100 countries, one from each country

• A multinational organization dedicated to worldwide agreement oninternational standards in a variety of fields

• Established in 1947

• Example of standards: ISO OSI Reference Model

Standards (4)

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ITU-T: International Telecommunications Union – Telecommunication Standards Sector• United Nations organization that develops standards for

telecommunication• Headquartered in Geneva, Switzerland• International organization whithin which governments & private

sectors coordinate global telecom networks and services• Activities include:

‣ Coordination, development, regulation and standardization of telecommunication

‣ Organization of regional & world telecom events

Standards (5)

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ITU-T: International Telecommunications Union – Telecommunication Standards Sector (cont)

• Example of standards:

‣ V-series: define data transmission over phone line

‣ X-series: define transmission over public digital networks

IEEE: Institute of Electrical and Electronics Engineers

• A non-profit, technical professional association of more than 377,000 individual members in 150 countries.

• Largest national profession group

• Example of standards: IEEE 802 series

Standards (6)

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IETF: Internet Engineering Task Force

• Standards body for the Internet itself

• A large open international community of network designers, operators, vendors, and researchers concerned with the evolution of the Internet architecture and the smooth operation of the Internet

• Develops and reviews specification intended as Internet Standards

• The actual technical work is done in its working groups, which are organized by topic into several areas (e.g. routing, network management, security, etc.)

• Most of the work is handled via mailing list, however, IETF also holds meetings three times per year

• Example of standards: RFC 2616 – HTTP protocol

Standards (7)

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ISOC: Internet Society

• International organization for global cooperation and coordination for the Internet and its internetworking technologies and applications

• Its members reflect the breadth of the entire Internet community and consist of individuals, corporations, non-profit organizations, and government agencies

• Its principal purpose is to maintain and extend the development and availability of the Internet and its associated technologies andapplications – both as an end in itself, and as a means of enabling organizations, professions, and individuals worldwide to more effective collaborate, cooperate, and innovate in their respective fields and interests

Standards (8)

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Pengantar – kuliah ke 2

• OSI model arsitektur

Lapisan dan struktur model

Fungsi setiap lapisan

Komunikasi Data

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• ISO has taken a model to overcome difficulties to test and modify softwares; since the software for a communication subsystem, were often based on a single, complex, unstructured program, (written in assembly language) with many interacting componentsThe communication subsystem here consists of a complex piece of hardware and software

• ISO Reference Model has taken a layered approach, where the complete communication subsystem is broken down into a number of layers, each of which performs a well-defined function

• Conceptually, each layers can be considered as performing generic functions:

Network-dependent functions

Application-oriented functions

ISO Reference Model

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• Three different operational environments:

Network environment: concern with the protocols and standards relating to the different types of underlying data communicationnetworks

OSI environment; include the network environment and adds additional application-oriented protocols and standards to allow end systems (computers) to communicate with one another in an open way

Real systems environment; build on the OSI environment and concerned with a manufacturer’s proprietary software and services; have been developed to perform a particular distributed information processing task

ISO Reference Model

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Diagram environment:

ISO Reference Model

Application-orientedfunctions

Network-dependentfunctions

AP AP

Network environment

OSI environment

Real systems environment

Data network

Computer A Computer B

Application-orientedfunctions

Network-dependentfunctions

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• Network-dependent and application-oriented (network-independent) components of the OSI model are implemented as a number of layers

• Each layer performs a well-defined function in the context of the overall communication subsystems; and has a well-defined interface with the layers immediately above and below

• The function of each layer is specified formally as a protocol that defines the set of rules and conventions used by the layer to communicate (exchanging messages, both user data and additional control information), with a corresponding (similar) peer layer in another (remote) system

• The implementation of a particular protocol layer is independent of all other layers

ISO Reference Model

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The logical structure of ISO Reference Model:

ISO Reference Model

Application layer

Presentation layer

Session layer

Transport layer

Network layer

Link layer

Physical layer

AL (7)

PL (6)

SL (5)

TL (4)

NL (3)

LL (2)

PL (1)

AP AP

Network environment

OSI environment

Real systems environment

Data network

Computer A Computer B

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• The network-dependent layers (three lowest layers) are concerned with the protocols associated with the data communication network being used to link the two communicating computers

• The application-oriented layers (three upper layers) are concerned with the protocols that allow two end-user application processes to interact with each other, normally through a range of services offered by the local operating system

• The intermediate transport layer (4) masks the upper application-oriented layers from the detailed operation of the lower network-dependent layers; it develops the services provided by providing the application-oriented layers with a network-independent message interchange service

ISO Reference Model

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Function of each layer of the OSI model:

End-user application process

File transfer, access and management, document and message interchange, job transfer and manipulation

Transfer syntax negotiation, data representation transformations

Dialog and synchronizationcontrol for application entities

End-to-end message transfer (connection management, error control, fragmentation, flow control)

Network routing, addressing, call set-up, and clearing

Data link control (framing, data transparency, error control)

Mechanical and electrical network interface definitions

Data communication network

Distributed information services

Syntax-independent message interchange services

Network-independent message interchange services

Physical connection tonetwork termination equipment

Application layer

Presentation layer

Session layer

Transport layer

Network layer

Link layer

Physical layer

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• Each layer provides a defined set of services to the layer immediately above; also uses the services provided by the layer immediately below it to transport the message units associated with the protocol to the remote peer layerexample: transport layer provides a network-independent message transport service to the session layer above it and uses the service provided by network layer below it to transfer a set of message units associated with the transport protocol to a peer transport layer in another system

ISO Reference Model

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• Network-dependent layers

Physical layer

Link layer

Network layer

• Application-oriented layers

Transport layer

Session layer

Presentation layer

Application layer

ISO Reference Model

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Physical layer

• Concern with the physical and electrical interfaces between the user equipment and the network terminating equipment

• Provide the link layer with a means of transmitting a serial bit stream between two equipments

• Examples: wires, connectors, voltages, data rates

ISO Reference Model

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Link layer• Develop a physical connection provided by the particular network to

provide network layer with a reliable information transfer facility• Responsible for functions such as error detection and retransmission

messages (if there is a transmission error)• Examples: physical addressing, network topology, error notification, flow

control• Two types of services:

Connectionless, treats each information frame as a self-contained entity that is transferred using a best-try approach. If errors are detected in a frame, then the frame is simply discardedConnection oriented, try to provide an error-free information transfer facility

ISO Reference Model

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Network layer

• Responsible for establishing and clearing a network wide connection between two transport layer protocol entities

• It includes functionality as network routing (addressing) and, flow control across the computer-to-network interface

• In internetworking, it provides various harmonizing functions between the inter-connected networks

ISO Reference Model

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Transport layer

• Interface between the higher application-oriented layers and the underlying network-dependent protocol layers

• Provide the session layer (one layer above) with a message transfer facility that is independent of the underlying network type; therefore transport layer hides the detailed operation of the underlying network from the session layer

• It offers a number of classes of service to compensate for the varying quality of service (QOS) provided by the network layers associated with the different types of network

• Five classes of services ranging from class 0 (provides only basic functions needed for connection establishment and data transfer) to class 4 (provides full error control and flow control procedures

ISO Reference Model

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Session layer• Interhost communication: establishes, manages and terminates sessions

between applications• Allows two application layer protocol entities to organize and synchronize

their dialog and manage their data exchange• Responsible for setting up (& clearing) a communication (dialog) channel

between two communicating application layer protocol entities (presentation layer protocol entities in practice) for the duration of the complete network transaction

• A number of optional services provided:Interaction management; data exchange associated with a dialog may be duplex or half-duplex (where each protocol here provides facilities for controlling the exchange of data/dialog units in a synchronized way)

ISO Reference Model

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Session layer

• A number of optional services provided:

Synchronization; for lengthy network transactions, the user (through the services provided by the session layer) may choose periodically to establish synchronization points associated with the transfer. If a fault develops during a transaction, the dialog may be restarted at an earlier synchronization point

Exception reporting; non-recoverable exceptions arising during a transaction can be signaled to the application layer by the session layer

ISO Reference Model

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Presentation layer

• Concerned with the representation (syntax) of data during transfer between two communicating application processes

• Data security; encrypted/enciphered (using a key) data sent is (hopefully) known only by the intended recipient presentation layer, and later the key is used to decrypts (deciphers) the received data before passing it onto the intended recipient

ISO Reference Model

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Application layer

• Provides the user interface (an application program/process) a range of network wide distributed information servicesexamples: file transfer access and management, general document and message interchange services (e-mail)

• The layer provides other services as:

Identification of the intended communication partner by name or by address

Determination of the current availability of an intended communication partner

Establishment of authority to communicate

Agreement on privacy (encryption) mechanism

ISO Reference Model

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Application layer

• The layer provides other services as:

Authentication of an intended communication partner

Selection of the dialog discipline, including the initiation and release procedures

Agreement on responsibility for error recovery

Identification of constraints on data syntax (character sets, data structures, etc.)

ISO Reference Model

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Data Encapsulation

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Data Encapsulation

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ISO vs TCP/IP Reference Model

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The importance of TCP/IPAlthough the OSI model is universally recognized, the historical and

technical open standard of the Internet is TCP/IP (Transmission Control Protocol/Internet Protocol)

The TCP/IP model and the TCP/IP protocol stack make data communication possible between any computers, anywhere in the world

Four layers in TCP/IP model:Application; Transport; Internet; Network

TCP/IP Reference Model

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Application layer• The designer felt that the higher level protocols should include the

session and presentation layer details• They created this layer that handles high-level protocols, issues of

representation, encoding and dialog control• The TCP/IP combines all application-related issues into one layer,

and assumes this data is properly packaged for the next layer


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Transport layer• It deals with the quality of service issues of reliability, flow control

and error correction• One of its protocols, the transmission control protocol (TCP), is a

connection-oriented protocol that provides excellent and flexible ways to create reliable, well-flowing, low-error network communications

• It dialogues between source and destination while packaging application layer information into units called segments


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Internet layer• It governs by the Internet protocol (IP)• Send source packets from any network on the internetwork and have

them arrive at the destination independent of the path and networks they took to get there

• Best path determination and packet switching• Example: when we mail a letter, we do not know how it gets there

(various possible routes), but we do care that it arrives


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Physical layer• It also called the host-to-network layer• Concerned with all issues that an IP packet requires to actually make

a physical link• This includes a LAN and WAN technology details, and all the

details in the OSI physical and data link layers


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• TCP/IP combines the presentation and session layer issues into its application layer

• TCP/IP combines the OSI data link and physical layers into one layer

• TCP/IP appears simpler because it has fewer layers• TCP/IP protocols are the standards around which the internet

developed, so the TCP/IP model gains credibility just because of its protocols.

Comparing TCP/IP with OSI

TRANSMISI DATA & TRANSMISI DATA & MEDIA TRANSMISIMEDIA TRANSMISI

TERMINOLOGI (1)

Network Devices

Terminologi (2)

Terminologi (3)

Frekuensi, Spektrum danBandwidth

Sinyal-Sinyal Kontinu danDiskrit

Sinyal Periodik

Gelombang Sinus

Keragaman Gelombang Sinus

Panjang Gelombang(Wavelength)

Frequency Domain Concepts

Add Frequency Component

Frequency Domain

Analog And Digital Data Transmission

Acoustic Spectrum

Signal

Data & Signal

Media on PC

EthernetModemPC Card (WLAN)DVB

Ethernet - Architecture

Ethernet – IEEE 802.3

10Base5 – Thick wire coaxial10Base2 – thin wire coaxial / cheaper net10BaseT – Twisted Pair10BaseF – Fiber Optics

100BaseT – Fast Ethernet

Ethernet – 10Base5

Ethernet – 10Base2

Ethernet – 10BaseT

NIC Connector type

Coaxial CableBayonet Nut Connector (BNC)

Twisted Pair CableRJ-45 (8 wire)

Fiber OpticsSMA connectors

Modem

Allows modems of different vendors to operate togetherDefine How modems operate:

Modulation techniquesData compression techniqueError detection strategy

Modem – Analog vs Digital

AnalogInfinite number of levelsConform to voice patternTimes from highest to lowest and back to the highest point in one second is the frequencyCan be transmitted over long distance

DigitalOnly two levels (high and low)Conforms to how computers operateCannot transmitted over long distance

Modem - Connection

Modem – Internal/External

PC Card – WLAN (802.11)

Bypassing last mile

PC Card (WLAN) - 1

PC Card (WLAN) - 2

PC Card (WLAN) – Indoor Antena

DVB – DVB/IP Tech

The Digital Video Broadcast over Internet Protocol (DVB/IP) system is functionally an IP-over-Ethernet simplex satellite service that incorporates frame-relay type traffic management. At its core, DVB is a modem-on-a-chip, plus an intelligent multiplexer. The antenna is typically a CATV dish, 2.4 -3.8 meters in diameter (for C-band), or 0.6 -1.8 meters (for Ku-band).

DVB – DVB/IP Routing

DVB - Adaptability

DVB – DVB Card

Media Transmisi

WiredTwisted Pair – UTPCoaxialFiber

WirelessMicrowaveSatellite

Twisted Pair

Two wired wrapped in a twisted fashion

Designed to reduce cross-talk due inductanceStill subject to interference from stray signal

Primarily used for local loop connections and LANsComparatively narrow bandwidth

UTP – Unshielded Twisted Pair

Pair 1White/blueBlue

Pair 2White/OrangeOrange

Pair 3White/GreenGreen

Pair 4White/BrownBrown

RJ45 Connector

UTP – Straight Cable

Wo/O Wg/B Wb/G Wbr/Br

UTP – Cross Cable

Wg/G Wo/B Wb/O Wbr/Br

UTP - CategoryCategory Maximum Data Rate Usual Application

CAT 1 Less than 1 Mbps Analog voice (POTS),

Integrated Services Digital Network Basic Rate Interface in ISDN

Doorbell wiring

CAT 2 4 Mbps Mainly used in the IBM Cabling System for token ring networks

CAT 3 16 Mbps Voice and data on 10BASE-T Ethernet

CAT 4 20 Mbps Used in 16 Mbps Token Ring

Otherwise not used much

CAT 5 100 Mbps 100 Mbps TPDDI (100BASE-T or Fast Ethernet)

1000 Mbps (4 pair) 155 Mbps ATM

Gigabit Ethernet

CAT 5E 100 Mbps 100 Mbps TPDDI (100BASE-T or Fast Ethernet)

155 Mbps ATM

CAT 6 200-250 MHz Super-fast Broadband Applications.

Coaxial

Center lead conducts the signalProtected by insulation and braded wire

Used mostly for television and connections to antennaLarger Bandwidth but large in size

Fiber Optical

Signal transmitted by photos rather than electronsDramatically higher bandwidthUsed mostly for backbone communication connections, very high speed LANs and fast network connections

Fiber Optical

Wireless Transmission

Microwave – Antenna (1)

Omni2.4GHz 8dBi


Sectoral14dBi 180deg


Sectoral17dBi 90deg


Direct (Grid)2.4 GHz 24dB

Microwave – Power AMP

Satellite - Broadband

Media Comparison

Multiplexer

HUBSwitchBridgeRouter

Hub versus Switch

Hub provide connection to all ports (i.e. in one port and out all other ports).

Passive hub – no signal regenerationActive hub – provide signal regeneration

Switch direct the message from appropriate port (directs a message from the input port to the desired output port).

More expensive but better bandwidth utilization

Hub versus Switch

LAN Hub device

LAN Switch device

Switch

Bridge – Access Point (WLAN)

Router

Connecting different segment Have different interfaces (Ethernet, WAN-Serial, Fiber, etc)Table Routing

Router

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Interface Komunikasi & Transmisi Data – kuliah ke 4Interface komunikasi

– Sumber redaman dan distorsiBeberapa tipe redaman dan distorsiPengaruh redaman dan distorsi pada sinyal

– Delay propagasi - pengaruhnya pada sinyalTransmisi Data

– Dasar transmisi data: beberapa tipe mode transmisi– Transmisi sinkron dan asinkron: persamaan & perbedaan– Teknik deteksi kesalahan: beberapa metode pendeteksian– Kompresi data: beberapa tipe algoritma kompresi

Komunikasi Data

2

Various attenuation & distortion effects that affects any signal carried on a transmission medium:

• Attenuation

• Limited bandwidth

• Delay distortion

• Noise

Attenuation & Distortion

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Attenuation

• Signal attenuation - if a signal that propagates along a transmission medium (line) gets an amplitude decreasing

• A limit is set on the length of cable that can be used to ensure that receiver can detect and interpret the received attenuated signalcorrectly

• If longer cable is needed, one or more amplifiers (=repeaters) are inserted at intervals along the cable to restore the received signal to its original level


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Attenuation

• Signal attenuation increases as a function of frequency; since signal consists of a range of frequencies

• Solutions:

– By designing amplifiers to amplify different frequency signals by varying amounts

– By using equalizers to equalize the attenuation across a defined band of frequencies


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Attenuation

• Measurement of attenuation and amplification (also known as gain) is in decibels (dB)

dBlog10nAttenuatio2

110 P

P= dBlog10ionAmplificat

1

210 P

P=

where P1 is the transmitted signal power level & P2 is the received power; both in watts.

• Therefore, decibels are dimensionless and simply a measure of the relative magnitude of the two power levels

• The use of logarithms means that the overall attenuation/amplification of a multisection transmission channel can be determined by summing together the attenuation/amplification of the individual sections

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Attenuation

• Each signal element can represent more than a single binary digit; e.g. when binary informations are transmitted over a limited-bandwidth channel such as the PSTN, we often use more than two signal levels.

• If the number of signal levels is M, then the number of bits per signal element m, is given by:

Mm 2log=

• The rate of change of the signal is known as the signaling rate (Rs); measured in baud.

MRR s 2log=

7


Limited bandwidth

• Any communications channel/transmission medium has a defined bandwidth associated with it; which specifies the band of sinusoidal frequency components that will be transmitted by the channel unattenuated

• Therefore, when transmitting data over a channel, it is needed to quantify the effect of the channel bandwidth on the transmitted data signal

• From the fourier analysis, it is known that any periodic binary sequence is made up of an infinite series of sinusoidal signals including the fundamental frequency component, f0, and its harmonic components.

8


Limited bandwidth

• When a binary signal is transmitted over a channel, only those frequency components that are within the channel bandwidth will be received

• From the figure: the larger the channel bandwidth, the higher-frequency components are received and the closer is the received signal to the original (transmitted) signal

• The maximum information transfer rate of noiseless transmission channel C, is given by Nyquist expression as:

Where W is the bandwidth of the channel in Hz, and M is the number of levels per signaling element

MWC 2log2=

9


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Limited bandwidth

• In practice, with binary data, extra bits are added for transmission control purposes; therefore the useful data rate is often less than the actual bit rate

• When information are transmitted over a communications channel, three rates are involved: the signaling rate, the bit rate, and the data rate; all of which may be the same or different

• Since the duration of each bit, Tb (in sec.), is the reciprocal of the bit rate, R, (in bps), then the bandwidth efficiency of a transmission channel, B, that defined as R/W, can be derived as :

1-Hz bps 1

bs WTWTm

WRB ===

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Limited bandwidth

• From the expression, it can be assumed that the higher the bit rate, relative to the available bandwidth, the higher bandwidth efficiency

• Typical values of B range from 0.25 to 3.0 bps Hz-1

where the first corresponding to a low bit rate relative to the available bandwidth, and the second a high bit rate that requires a relatively high signaling rate

• In general, the higher the bandwidth efficiency, the stricter are the design parameters of the associated equipment and hence the higher cost


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Delay distortion

• When a digital signal is transmitted, the various frequency components making up the signal arrive at the receiver with varying delays. This results in delay distortion of the received signal

• The amount of distortion increases as the bit rate of the transmitted data increases, since some of the frequency components associated with each bit transition are delayed and start to interfere with the frequency components associated with a later bit

• It also called intersymbol interference, since the received signal, that is normally sampled at the nominal center of each bit cell, can lead to incorrect interpretation of the received signal as the bit rate increases


13


Noise

• Line noise level, a random perturbations that present on the line even when no signal is being transmitted

• Signal-to-noise ratio (SNR) is the ratio of the average power in a received signal S, to the power in the noise level N; normally expressed in decibels; given as:

dB ⎟⎠⎞

⎜⎝⎛=

NSSNR 10log10

14


Noise

• High SNR means a high power signal relative to the existing noise level, resulting a good-quality received signal; on the other hand, a low SNR means a low-quality received signal

• Shannon-Hartley law is the expression to determine the theoreticalmaximum information (data) rate of a transmission channel related to the SNR ratio; given as:

where C is the information (data) rate [bps], W is the bandwidth of the line channel [Hz], S is the average signal power [watts] and N is the random noise power [watts]

bps ⎟⎠⎞

⎜⎝⎛ +=

NSWC 1log 2

15

Noise examples:

• Near-end crosstalk (NEXT) or self-crosstalk, caused by the strong signal output by a transmitter circuit being coupled and interfered with the much weaker signal at the input to the local receiver input

• Impulse noise, caused by impulses of electrical energy associated with external activity or equipment being picked up by a signal line. Ex: switching circuits in old telephone exchanges (loud clicks on the line, etc)

• Thermal noise, caused by the thermal agitation of electrons associated with each atom in the device or transmission line material.- present in all electronic devices and transmission media- all transmission media experience this noise at all temperatures above absolute zero


16

Noise examples:

• - this noise is also known as white noise, since it is made up of random frequency components (across the complete frequency spectrum) ofcontinuously varying amplitude

In practice, it is important to determine the minimum signal level that must be used (relative to the noise level), to achieve a specific minimum bit error rate ratio

bit error rate ratio is an acceptable low probability that a single bit will be misinterpreted by the receiver over a defined periodex: a bit error rate ratio of 10-4 means that, on average, 1 bit in every 104 received will be misinterpreted


17


Noise• The energy per bit in a signal, Eb is given by:

where S is the signal power [watts] and Tb is the time period for 1 bit [seconds], R is the data transmission rate that is equal to 1/T

• The noise power density [watts Hz-1], the level of (thermal) noise in a bandwidth of 1 Hz in any transmission line is given by:

where k is Boltzmann’s constant (1.3803 x 10-23 joule K-1) and T is the temperature [K]

• From these, to quantify the effect of noise, the energy per bit Eb is expressed as a ratio of the noise energy per Hz, N0 :

second]-[watt [joules] RSSTE bb ==

]Hz[watt -1kTN =0

18


Noise

• The effect of noise, the energy per bit Eb is expressed as a ratio of the noise energy per Hz, N0 :

Or in decibels:

• It can be seen that, to achieve an acceptable Eb / N0 ratio (hence minimum bit error rate), the signal power level S is needed with increasing of the temperature T and bit rate R

kTR

S

NR

S

NEb ==

00

( )kT[dB] 10100

log10log10 −⎟⎠⎞

⎜⎝⎛=

RS

NE b

19


Noise

• Since N0 is the noise power density [watts Hz-1] and a channel of bandwidth is W Hz, the noise power in a received signal N given by N = W N0 then

• Or in decibels:

RW

NS

NE b =

0

RWNS

NE b

1010100

log10log10log10 −+⎟⎠⎞

⎜⎝⎛=[dB]

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Propagation delay

• There is always a short but finite time delay for a signal (electrical, optical or radio) to propagate (travel) from one end of a transmission medium to the other; known as the transmission propagation delay, Tpof the medium

• Round-trip delay is the time delay between the first bit of a block being transmitted by the sender and the last bit of its associated acknowledgement being receivedThe function is not only of the time taken to transmit the frame at the link bit rate (known as the transmission delay, Tx) but also of the propagation delay of the link Tp

• The relative weighting of the two varies for different types of data link and hence the two times varies for different are often express as a ratio a:

21

Propagation delay

• The relative weighting of the two varies for different types of data link and hence the two times varies for different are often express as a ratio a:

secondper bitsin ratebit link ed transmittbe tobits ofnumber

andsecondper metersin n propagatio ofvelocity

metersin separation physical

where

RNT

VST

TT

a

x

p

x

p

=

=

=

• If a < 1: the round trip delay is determined primarily by the transmission delay

• If a = 1: both delays have equal effect

• If a > 1: the propagation delay dominates

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• In data communication, the term ‘data’ is reserved for describing a set/a block of one/more digitally encoded alphabetic and numericcharacters that being exchanged between two devices

• When a data communication facility is used to transfer this type of data, the two communicating parties (DTEs) must also exchange control messages (i.e. to overcome the effect of transmission errors) within the communication facility

Data Transmission

Keyboard

Encode

Coded bit patterns:codewords

- EBCDIC (ExtendedBinary Coded DecimalInterchange Code)- ASCII (AmericanStandards Committee forInformation Interchange)

Decode

Printer

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• Transfer modes:

– Parallel transmission mode: multiple wires connected to each subunit, and separate wire carries each bit of data; results in minimal delays

– Serial transmission mode: use a single pair of lines; the data is transmitted in a single bit of time using a fixed time interval for each bit

Data Transmission

24

• Communication modes:

– Simplex: used when data is to be transmitted in one direction only; i.e. in a data logging system in which a monitoring device returns a reading at regular intervals to the data gathering facility

– Half-duplex: used when the two interconnected devices wish to exchange information (data) alternately; i.e. if one of the devices returns some data only in response to a request from the other. The two devices must be able to switch between send and receive modes after each transmission

– Duplex/full-duplex: used when data is to be exchanged between the two connected devices in both directions simultaneously; i.e. if for throughput reasons data can flow in each direction independently

Data Transmission

25

• For the receiving device to decode and interpret the pattern correctly, it must be able to determine:

– The start of each bit cell period (in order to sample the incoming signal in the middle of the bit cell): bit or clock synchronization

– The start and end of each element (character or byte): character or byte synchronization

– The start and end of each complete message block (frame): blockor frame synchronization

• Transmission modes: synchronization method determined whether the transmitter and receiver clocks are independent (asynchronous) or synchronised (synchronous)

Data Transmission

26

• Two different transmission modes:

– Asynchronous transmission: each character (byte) is treated independently for clock (bit) and character (byte) synchronization purposes and the receiver resynchronizes at the start of each character received

– Synchronous transmission: the complete frame (block) of characters is transmitted as a contiguous string of bits and the receiver endeavors to keep in synchronism with the incoming bit stream for the duration of the complete frame (block)

Data Transmission

27

• Error control:

– Need mechanism to detect when a bit is in error (parity bits, block checksums, etc)

– parity bit: used in an asynchronous transmission, where a binarydigit (bit) is added within each transmitted character

– error check sequence: used in a synchronous transmission, where possible transmission errors on the complete frame, as the basicunit of transmission is in frame

– Another schemes are exist to enable the receiver to obtain another copy of the original transmission when errors are detected

Data Transmission

28

• Flow control:

– The receiver may not be able to handle all the information sent due to limited processing power, buffer space, etc.

– the control of the flow information between two DTEs when the two devices operate at different data rates; i.e. control of the mean output rate of the faster device, to prevent the communication network becomes congested

– need when two devices are communicating through an intermediate network, as often the network will buffer only a limited amount of data

– method to control the flow data transfer to ensure that the receiver does not lose any of the transmitted data because the receiving device has insufficient storage

Data Transmission

29

• Data link protocols

– protocol: a set of conventions or rules that must be adhered to by both communicating parties to ensure that information being exchanges across a serial data link is received and interpreted correctly

– defines: error and flow control;data format (number of bits per element and type of encoding scheme being used);type and order of messages that are to be exchanged in order to achieve reliable (error free and no duplicates) information transfer between two communicating parties.

Data Transmission

30

Asynchronous Transmission

• Use when the data to be transmitted is generated at random intervals; i.e. a user at a keyboard communicating with a computer

• Each transmitted character/byte is encapsulated between an additional start bit and one or more stop bits

• The polarity of the start and stop bits is different; to ensures that there is always a minimum of one transition (1 0 1) between each successive characters

31


• Baud: the number of line signal transitions per second; if each transmitted signal can be in one of two states, baud and bits per second (bps) are equivalent.

• In general, signaling rate is more general to use, since it avoid confusion. The data or information transfer rate represents the number of data bits per second (bps).I.e. a signaling rate of 300 baud with 4 bits per signaling element would yield a data rate of 1200 bps.

• To achieve bit and character synchronization, the receiving transmission control circuit must be set to operate with the same characteristics as the transmitter in terms of the number of bits per character and the bit rate being used

32


Bit synchronization

• The receiver clock runs asynchronously with respect to the incoming signal. In order for the reception process to work reliably, a scheme whereby the local receiver clock samples the incoming signal as near to the center of the bit cell as possible

33


Bit synchronization

• Since the receiver clock (RxC) is running asynchronously with respect to the incoming signal (RxD), the relative positions of the two signals can be anywhere within the single cycle of the receiver clock.

• The higher the clock rate ratio, the nearer the sampling instant will be to the nominal bit cell center.

• The maximum bit rate normally used with this transmission is 19.2 kbps.

34


Character synchronization

• The receiving transmission control circuit is programmed to operate with the same number of bits per character and the same number of stop bits as the transmitter.

• After the start bit has been detected and received, the receiverachieves character synchronization simply by counting the programmed number of bits.

• It then transfers the received character (byte) into a local buffer register and signals to the controlling device (e.g. microprocessor) that a new character (byte) has been received.

• It then awaits the next line signal transition that indicates a new start bit (and character) is being received

35


Frame synchronization

• Here, the receiver must be able to determine the start and end of each frame

• Example of transmitting blocks of printable characters encapsulated by the complete block between two special (nonprintable) transmission control characters: STX (start-of-text; indicates the start of a new frame after an idle period) and ETX (end-of-text; indicates the end of the frame)

• In transmitting binary data, the two transmission control characters STX and ETX are each preceded by a third transmission control character DLE (data link escape)

36


Frame synchronization

• Character/byte stuffing: On receipt of each byte after the DLE-STX start-of-frame sequence, the receiver determines the next character/byte. If it is a DLE, the receiver processes the next byte to determine whether that is another DLE or ETX. If it is a DLE, the receiver discards it and awaits the next byte. If it is an ETX, this is taken as the end of the frame.

37

Synchronous Transmission

• Use in transmission of large blocks of data at higher bit rates; the complete block or frame of data is transmitted as a contoguous bit stream with no delay between each 8-bit element.

• To enable the receiving device to achieve the various level of synchronization:

– The transmitted bit stream is suitable encoded so that the receiver can be kept in synchronism

– All frames are preceded by one or more reserved bytes/charactersfor byte/character synchronization (to ensure the receiver reliably interprets the received bit stream on the correct byte/characterboundaries

– The contents of each frame are encapsulated between a pair of reserved character/byte synchronization

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Synchronous Transmission

• During the period between the transmission of successive frames,either synchronous idle characters/bytes are continuously transmitted to allow the receiver to retain bit and byte synchronism; or each frame is preceded by two or more special synchronizing bytes or characters to allow the receiver to regain synchronism

39

Error Detection

• The concept behind error control is the prevention of delivery of incorrect messages (bits) to a higher level in the communicationhierarchy

• Two factors that determine the type of error-detection techniques:

– Bit Error Rate (BER); whether the errors occur as random single-bit errors

– Burst Error; whether the errors occur as groups of contiguous strings of errors

• The BER is the probability P of a single bit being corrupted in a defined time interval. BER of 10-13 means that, on average, 1 bit in 103

will be corrupted during a defined time period

40

Error Detection

• Two approaches to achieve a copy of (hopefully) correct information:

– Forward error control; each transmitted character/frame containsadditional (redundant) information so that the receiver can not only detect when errors are present but also determine where in the received bit stream the errors are. The correct data is obtained by inverting these bits. In practice, the number of additional bits, required to achieve reliable forward error control, increases rapidly as the number of information bits increases

– Feedback (backward) error control; each character/frame includesonly sufficient additional information to enable the receiver todetect when errors are present but not their location. A retransmission control scheme is used to request that another copy of information be sent

41

Error Detection

• Widely used error detection schemes: parity, check sum, cyclic redundancy check

Parity

• Extra bit at the end of a character (5-7 bits) specifying how many of the bits are 1’s

• The parity bit is said to be even if it is set to make the total number of 1’s even, and oddif it is set to make the total number of 1’s odd.

• Can detect all odd numbers of bit errors in the message

• Can not detect even numbers of bit errors – error cancellation

• Hamming distance: number of bits in which two words differ

• Typically used in asynchronous transmission, since timing and spacing between characters is uncertain.

42

Error Detection

• Typically used in asynchronous transmission, since timing and spacing between characters is uncertain.

43

Error Detection

Parity

44

Error Detection

Block Sum Check

• Block error rate: the probability of a block containing an error

• Block (sum) check character check the error by using a vertical parity check that calculates parity over the same bit of multiple characters.

• Used in conjunction with longitudinal parity check.

• Overhead is related to number of bits and can be large

45

Error Detection

Cyclic Redundancy Check (CRC)

• Parity bits still subject to burst noise, uses large overhead (potentially) for improvement of 2-4 orders of magnitude in probability of detection

• CRC is based on a mathematical calcilation performed on message. The following terms will be used:

– M – message to be sent (k bits)

– F – Frane check sequence (FCS) to be appended to message (nbits)

– T – Transmitted message includes both M and F (k+n bits)

– G – a (n+1) bit pattern (called generator) used to calculate F and check T

46

• Mainly done in applications that involve public transmission facilities, such as PSTN, where charges are based on time (duration) and distance. If the time to transmit each block of data can be reduced, it will reduce the call cost

• In practice, a range of compression algorithm can be applied, each suited to a particular type of data

• Some modems (intelligent modems) now offer an adaptive compression feature which selects a compression algorithm to suit the type of data being transmitted

• Some common types of data compression algorithm:

Data Compression

47

Packed decimal

• Used to compress a frame contain only numeric characters

• It reduces the number of bits per character from seven (ASCII) to four by using a binary-coded-decimal (BCD); all have 011 in their three high-order bit positions

Data Compression

48

Relative encoding

• Send only the magnitude difference between each value together with a known reference value

• Effective for data logging applications; ex. monitoring the water level of a river

• In general, binary values with a bit-oriented protocol produce the largest saving

Data Compression

49

Character suppression

• A variation of the relative encoding scheme; use in a more general way to compress other character types

• In transmitting frames contain printable characters, there are often sequences in the frame when the same character repeats; e.g. the space character. The control device at the transmitter scans the framecontents prior to transmission and, if a contiguous string of three or more characters is located, replaces these with the three-character seq.

Data Compression

50

Huffman coding

• Exploits the property that not all symbols in a transmitted frame occur with the same frequency e.g. in a frame comprising strings of characters, certain characters occur more often than others.

• Instead of using a fixed number of bits per character, a statistical encoding scheme is used, where the most common characters are encoded using fewer bits than less frequent characters.

• The character string to be transmitted is analyzed and the character types and their relative frequency is determined. The coding operation then creates an unbalanced tree with some branches (as codewords) shorter than others. The degree of imbalance is a function of the relative frequency of occurrence of the characters; the larger the spread, the more unbalanced is tree huffman code tree

Data Compression

51

Huffman coding

• Huffman (code) tree is a binary tree with branches assigned the value 0 or 1. The base of the tree (at geometric top), is known as root node, and the point where a branch divides is a branch node. The termination point of a branch is known as a leaf node, where the symbols being encoded are assigned.

• The theoretical minimum average number of bits per codeword to transfer message string is known as the entropy, H, of the message.

• The formula to calculate H is derived by Shannon:

(bits per codeword)

Where n is the number of characters in the message and Pi is the probability of character (i) occuring in the message.

Data Compression

i

n

ii PPH 2

1log∑

=

=

52

Huffman coding

• It is most efficient when frequency distribution of the characters being transmitted is wide and long character strings are involved; it is not suitable for the transmission of binary-coded computer data since the 8-bit bytes generally occur with about the same frequency

Data Compression

53

Dynamic Huffman Coding

• Problem with basic Huffman encoding is that transmitter and receiver must know the code tree; here, updates Huffman tree dynamically.

• With this method, if the character to be transmitted is currently present in the tree, its codeword is determined and sent in the normal way. If the character is not present (its first occurrence), the character I transmitted in its uncompressed form.

• The encoder updates its Huffman tree either by incrementing the frequency occurrence of the transmitted character or by introducing the new character into the tree.

• This means that the savings in transmission bandwidth start only when characters begin to repeat themselves; I.e. in transmitting the text files

Data Compression

54

Fascimile compression

• Effective for data logging applications

• In general, binary values with a bit-oriented protocol produce the largest saving

Data Compression

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