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
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
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; 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 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
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, 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;
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)