KOMUNIKASI DATA

Chapter 1Introduction

GBPPSAP

What is data communication? Adalah bagian dari telekommunikasi yang

melingkupi transmission of data ke dan dari computers dan components sistem komputer.

More specifically data communication is transmitted via mediums such as wires, coaxial cables, fiber optics, or radiated electromagnetic waves such as broadcast radio, infrared light, microwaves, and satellites.

History of Telecommunications Invention of telegraph Samuel Morse – 1837 Invention of telephone- Alexander Graham

Bell – 1876 Development of wireless By ??? – 1896 Concept of universal access and growth of

AT&T

History of Telecommunications Continued…. Three main developments that led to the

growth of data communications systems: Large-scale integration of circuits reduced the

cost and size of terminals and comm equipment

Developments of software systems made establishment of communication networks easy

Competition among providers of transmission facilities reduced the cost of data circuits

A Communications Model Source : generates data to be transmitted Transmitter : Converts data into

transmittable signals Transmission System : Carries data Receiver : Converts received signal into data Destination : Takes incoming data

Simplified Communications Model - Diagram

Key Communications Tasks Transmission System Utilization Interfacing Signal Generation Synchronization Exchange Management Error detection and correction Addressing and routing Recovery Message formatting Security Network Management

Key Data Communication Concepts Session: communication dialog between network users or

applications Network: interconnected group of computers and

communication devices Node: a network-attached computer Link: connects adjacent nodes (see Figure 1-4) Path: end-to-end route within a network Circuit: the conduit over which data travels Packetizing: dividing messages into fixed-length packets

prior to transmission over a network’s communication media

Routing: determining a message’s path from sending to receiving nodes.

Simplified Data Communications Model

Networking

Point to point communication not usually practical Devices are too far apart Large set of devices would need impractical number of

connections Solution is a communications network

Simplified Network Model

Wide Area Networks Large geographical area Crossing public rights of way Rely in part on common carrier circuits Alternative technologies

Circuit switching Packet switching Frame relay Asynchronous Transfer Mode (ATM)

Circuit Switching

Dedicated communications path established for the duration of the conversation e.g. telephone network

Packet Switching Data sent out of sequence Small chunks (packets) of data at a time Packets passed from node to node

between source and destination Used for terminal to computer and

computer to computer communications

Frame Relay

Packet switching systems have large overheads to compensate for errors

Modern systems are more reliable Errors can be caught in end system Most overhead for error control is stripped out

Asynchronous Transfer Mode (ATM)

Evolution of frame relay Little overhead for error control Fixed packet (called cell) length Anything from 10Mbps to Gbps Constant data rate using packet switching

technique

Local Area Networks Smaller scope

Building or small campus Usually owned by same organization as

attached devices Data rates much higher Usually broadcast systems Now some switched systems and ATM are

being introduced

Protocols Used for communications between entities

in a system Must speak the same language Entities

User applications, e-mail facilities, terminals Systems

Computer, Terminal. Remote sensor

Key Elements of a Protocol Syntax

Data formats Signal levels

Semantics Control information Error handling

Timing Speed matching Sequencing

Protocol Architecture Task of communication broken up into modules For example file transfer could use three

modules File transfer application Communication service module Network access module

Simplified File Transfer Architecture

A Three Layer Model Network Access Layer Transport Layer Application Layer

Network Access Layer Exchange of data between the computer

and the network Sending computer provides address of

destination May invoke levels of service Dependent on type of network used (LAN,

packet switched etc.)

Transport Layer

Reliable data exchange Independent of network being used Independent of application

Application Layer Support for different user applications

e.g. e-mail, file transfer

Addressing Requirements

Two levels of addressing required Each computer needs unique network address Each application on a (multi-tasking) computer

needs a unique address within the computer The service access point or SAP

Protocol Architectures and Networks

Protocols in Simplified Architecture

Protocol Data Units (PDU) At each layer, protocols are used to

communicate Control information is added to user data at

each layer Transport layer may fragment user data Each fragment has a transport header added

Destination SAP Sequence number Error detection code

This gives a transport protocol data unit

Network PDU

Adds network header network address for destination computer Facilities requests

Operation of a Protocol Architecture

TCP/IP Protocol Architecture Developed by the US Defense Advanced

Research Project Agency (DARPA) for its packet switched network (ARPANET)

Used by the global Internet Consist of :

Application layer Host to host or transport layer Internet layer Network access layer Physical layer

Physical Layer Physical interface between data

transmission device (e.g. computer) and transmission medium or network

Characteristics of transmission medium Signal levels Data rates etc.

Network Access Layer

Exchange of data between end system and network

Destination address provision Invoking services like priority

Internet Layer (IP)

Systems may be attached to different networks Routing functions across multiple networks Implemented in end systems and routers

Transport Layer (TCP)

Reliable delivery of data Ordering of delivery

Application Layer Support for user applications

e.g. http, SMPT

TCP/IPProtocol Architecture Model

OSI Model

Open Systems Interconnection Developed by the International

Organization for Standardization (ISO) Seven layers A theoretical system delivered too late! TCP/IP is the de facto standard

OSI Layers

Application Presentation Session Transport Network Data Link Physical

OSI v TCP/IP

Standards Required to allow for interoperability

between equipment Advantages

Ensures a large market for equipment and software

Allows products from different vendors to communicate

Disadvantages Freeze technology May be multiple standards for the same thing

Copyright 2007 John Wiley & Sons, Inc. 1 - 44

Types of Standards

Formal standards Developed by an industry or government

standards-making body De-facto standards

Emerge in the marketplace and widely used Lack official backing by a standards-making

body

Zulhelman 1 - 45

Standardization Processes Specification

Developing the nomenclature and identifying the problems to be addressed

Identification of choices Identifying solutions to the problems and

choose the “optimum” solution Acceptance

Defining the solution, getting it recognized by industry so that a uniform solution is accepted

Zulhelman 1 - 46

Major Standards Bodies ISO (International Organization for

Standardization) Technical recommendations for data communication

interfaces Composed of each country’s national standards orgs. Based in Geneva, Switzerland (www.iso.ch)

ITU-T (International Telecommunications Union –Telecom Group Technical recommendations about telephone, telegraph

and data communications interfaces Composed of representatives from each country in UN Based in Geneva, Switzerland (www.itu.int)

1 - 47

Major Standards Bodies (Cont.) ANSI (American National Standards Institute)

Coordinating organization for US (not a standards- making body)

www.ansi.org IEEE (Institute of Electrical and Electronic

Engineers) Professional society; also develops mostly LAN

standards standards.ieee.org

IETF (Internet Engineering Task Force) Develops Internet standards No official membership (anyone welcome) www.ietf.org

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Some Data Comm. StandardsLayer Common Standards

5. Application layerHTTP, HTML (Web)MPEG, H.323 (audio/video)IMAP, POP (e-mail)

4. Transport layer TCP (Internet)SPX (Novell LANs)

3. Network layer IP (Internet)IPX (Novell LANs)

2. Data link layerEthernet (LAN)Frame Relay (WAN)PPP (dial-up via modem for MAN)1. Physical layerRS-232c cable (LAN)Category 5 twisted pair (LAN)V.92 (56 kbps modem)

Zulhelman 1 - 49

Emerging Trends in Networking

Pervasive Networking Integration of Voice, Video and Data Information Services

Zulhelman 1 - 50

Pervasive Networking Means “Networks will be everywhere” Exponential growth of Network use Many new types of devices will have

network capability Exponential growth of data rates for all

kinds of networking Broadband communications

Use circuits with 1 Mbps or higher (e.g., DSL)

Zulhelman 1 - 51

Integration of Voice, Video & Data

Also called “Convergence” Networks that were previously transmitted using

separate networks will merge into a single, high speed, multimedia network in the near future First step largely complete

Integration of voice and data Next step

Video merging with voice and data Will take longer partly due to the high data rates required

for video

Zulhelman 1 - 52

Information Services World Wide Web based

Many new types of information services becoming available Services that help ensure quality of information

received over www Application Service Providers (ASPs)

Develop specific systems for companies such as providing and operating a payroll system for a company that does not have one of its own

Information Utilities (Future of ASPs) Providing a wide range of info services (email, web,

payroll, etc.)

Zulhelman 1 - 53

Implications for Management Embrace change and actively seek to use new aspects of

networks toward improving your organization Information moved quickly and easily anywhere and anytime Information accessed by customers and competitors globally

Use a set of industry standard technologies Can easily mix and match equipment from different vendors Easier to migrate from older technologies to newer technologies Smaller cost by using a few well known standards

Network Applications The network applications environment

consists of several important components: Application programs Operating systems Data communication systems Database management systems

The application environment is illustrated in Figure 1-10

Online System Requirements Response Time Throughput Consistency Flexibility Availability Reliability

Mean time between failure (MTBF) Mean time to repair (MTTR) Fault Tolerance

Recovery Security

Business Data Communication Applications Major data communication applications

include: E-mail Groupware Knowledge management systems E-commerce and e-business applications Wireless applications

Groupware Applications Group calendar

systems Electronic filing

cabinets Project

management software

Group support systems

Electronic meeting and videoconferencing systems

Document management systems (image processing systems)

Other Data Communication Applications Batch applications Data entry

applications Distributed

applications Inquiry/response

applications

Interactive applications

Sensor-based applications

Combined applications

Application Service Providers Many businesses have turned to third-

party services for some or all of their business and data communications applications

Application service providers (ASPs) are third-party organizations that manage and distribute software and services to other companies over the Web

Many ASPs specialize in integrated e-commerce and e-business applications

Business Data Communications IssuesMajor data communications issues

include: Cost-effectiveness The Internet Bandwidth Evolving technologies Convergence Standards Privacy and security

Business Data Communication CareersThere are numerous job opportunities and

career paths for individuals interested in data communications and networking

Table 1-6 includes examples of data communication job titles

Table 1-7 summarizes some of the major professional certifications for networking and data communications specialists

Further ReadingStallings, W. Data and Computer Communications

(6th edition), Prentice Hall 1999 chapter 1Web site for Stallings book

www.shore.net/~ws/DCC6e.htmlWeb sites for IETF, IEEE, ITU-T, ISOInternet Requests for Comment (RFCs)Usenet News groups

comp.dcom.* comp.protocols.tcp-ip