Chapter 1: Introduction

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Angela Hodges
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1 EE4272: Computer Networks Chapter 1: Introduction Instructor: Tricia Chigan Dept.: Elec. & Comp. Eng. 1) Data Communications: Deals with the transmission of signals in a reliable & efficient manner. Topics: Signal Transmission; Transmission Media; Signal Encoding; Interfacing; Data Link Control; Multiplexing 2) Networking: Deals with the technology & architecture of the communications networks used to interconnect communicating devices Topics: LANs; WANs; 3) Communications Protocols: Protocol Architectures; Analysis of individual protocols at various layers of the architecture Simplified Communications Model - Diagram A Communications Model Purpose of Com. Sys.: Exchange of data between parties. Source - Generates data to be transmitted. E.g., Phone, computer Transmitter - Converts data into transmittable signals. E.g., encode bit stream into electromagnetic signals. Transmission System - Carries data. E.g., transmission line, or a complex network Receiver - Converts received signal into data readable to des. device. Destination - Takes incoming data

2 Key Communications Tasks Simplified Data Communications Model Transmission System Utilization: efficient/fair facility sharing Signal Generation Synchronization Exchange Management Error detection and correction Addressing and routing Recovery Message formatting Security Network Management Reading assignment: read the details of P6-p7 Networking Wide Area Networks 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 Large geographical area Crossing public rights of way Rely in part on common carrier circuits Alternative technologies: all about resource sharing Circuit switching: Dedicated communications path established for the duration of the conversation. e.g. telephone network Packet switching: Date are sent out in a sequence of packets; Each packet passes through the network along some path; Used for terminal-to-computer, or computer-to-computer comm. Frame relay (up to 2 Mbps): reading assignment p10 Asynchronous Transfer Mode (ATM): reading assignment p11

3 Local Area Networks Protocols Smaller scope - Building or small campus Usually owned by same organization as attached devices Data rates much higher Usually broadcast systems (e.g. Ethernet Bus) Now some switched systems (e.g. Gigabit Ethernet Switch ) and ATM are being introduced Used for communications between entities in a system Entities: User applications; facilities; terminals Systems: Computer; Terminal; Remote sensor Must speak the same language Key Elements of a Protocol: -Syntax: Data formats; Signal levels -Semantics: Control information; Error handling - Timing: Speed matching; Sequencing Protocol Architecture Framework about how a set of protocols work together to finish the communication task between source and destination Three Protocol Architectures: - Three-Layer Model - TCP/IP Protocol Architecture - OSI Model 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 No official model but a working one. Application layer: logic needed to support various user applications Host to host or transport layer: reliable end-to-end delivery mechanisms, e.g. TCP Internet layer: provide routing function across multiple networks Network access layer: concern the exchange of date between end system & the network to which it is attached Physical layer: Physical interface between a data trans. device & a trans. medium or network

4 TCP/IP Protocol Architecture Model OSI Model Open Systems Interconnection : A framework for developing protocol standards. Developed by the International Standardization Organization (ISO) Seven layers A theoretical system delivered too late! TCP/IP is the de facto standard OSI Layers OSI v TCP/IP Application: e.g. web browser, , file transfer Presentation: provides independence to the app. processes from differences in data representation (syntax). Session: Provides control structure for comm. between applications; establish, manages, and terminates connections (sessions) between cooperating applications Transport: end-to-end reliable delivery control Network: routing/switching; establish/maintain/terminate connections Data Link: reliable transfer of information across the physical links; send frames with necessary synch., error control, and flow control Physical: concern with transmission of unstructured bit stream over physical medium;

5 Standards Standards Organizations Required to allow for interoperability between equipments 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 Internet Society ISO ITU-T (formally CCITT) ATM forum IETF Further Reading Resource Web sites for IETF, IEEE, ITU-T, ISO Internet Requests for Comment (RFCs)

Computer Networks. Introduction to Network. Dr. Adel Gaafar Abd Elrahim

Computer Networks. Introduction to Network. Dr. Adel Gaafar Abd Elrahim Computer Networks Introduction to Network Dr. Adel Gaafar Abd Elrahim A Communications Model Source generates data to be transmitted Transmitter Converts data into transmittable signals Transmission System