EE 4272 Computer Networks Instructor Tricia Chigan Dept

EE 4272: Computer Networks Instructor: Tricia Chigan Dept. : Elec. & Comp. Eng. Spring, 2003 3/15/2018 Spring, 2003 EE 4272

Chapter 1: Introduction 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 3) communications networks used to interconnect communicating devices Topics: LANs; WANs; 3) Communications Protocols: Protocol Architectures; Analysis of 4) individual protocols at various layers of the architecture 3/15/2018 Spring, 2003 EE 4272

Simplified Communications Model - Diagram Purpose of Com. Sys. : Exchange of data between parties. 3/15/2018 Spring, 2003 EE 4272

A Communications Model • 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 3/15/2018 Spring, 2003 EE 4272

Key Communications Tasks • 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 P 6 -p 7 3/15/2018 Spring, 2003 EE 4272

Simplified Data Communications Model 3/15/2018 Spring, 2003 EE 4272

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 3/15/2018 Spring, 2003 EE 4272

Wide Area Networks • • Large geographical area Crossing public rights of way Rely in part on common carrier circuits Alternative technologies: all about resource sharing Ø Circuit switching: Dedicated communications path established for the duration of the conversation. e. g. telephone network Ø 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. Ø Frame relay (up to 2 Mbps): reading assignment p 10 Ø Asynchronous Transfer Mode (ATM): reading assignment p 11 3/15/2018 Spring, 2003 EE 4272

Local Area Networks • 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 3/15/2018 Spring, 2003 EE 4272

Protocols • • • Used for communications between entities in a system Entities: User applications; e-mail 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 3/15/2018 Spring, 2003 EE 4272

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 3/15/2018 Spring, 2003 EE 4272

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. Ø Ø Application layer: logic needed to support various user applications Host to host or transport layer: reliable end-to-end delivery mechanisms, e. g. TCP Ø Internet layer: provide routing function across multiple networks Network access layer: concern the exchange of date between end Ø Physical layer: Physical interface between a data trans. device & a Ø system & the network to which it is attached trans. medium or network 3/15/2018 Spring, 2003 EE 4272

TCP/IP Protocol Architecture Model 3/15/2018 Spring, 2003 EE 4272

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 3/15/2018 Spring, 2003 EE 4272

OSI Layers • Application: e. g. web browser, email, 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; 3/15/2018 Spring, 2003 EE 4272

OSI v TCP/IP 3/15/2018 Spring, 2003 EE 4272

Standards • Required to allow for interoperability between equipments • Advantages Ø Ensures a large market for equipment and software Ø Allows products from different vendors to communicate • Disadvantages Ø Freeze technology Ø May be multiple standards for the same thing 3/15/2018 Spring, 2003 EE 4272

Standards Organizations • 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) 3/15/2018 Spring, 2003 EE 4272