Transcript WB_intro
CS3502: Data and Computer Networks INTRODUCTION introduction: CS3502 overview course of computer networks Track objectives homeworks, tests, grading approximate schedule objectives: CS3502 gain good overview of networking detailed knowledge of physical layer data link layer local area networks elementary protocol specification and elementary performance analysis analysis homeworks, etc: CS3502 homeworks passed out in class OR in electronic form. NOT GRADED. solutions for majority of homeworks provided. 3 tests spaced roughly 1/3 of quarter tests based - in order of priority- on homeworks class text notes, lectures introduction: CS3502 network definitions classifications models (high level) ISO model DOD model IEEE model purposes of networks network industries communication protocols Basic Terms Communication- moving information from one physical node to another Information - data Data - a pattern of 0’s and 1’s Node - a physical system for holding information Data - moving data from one physical node to another Communication Data Processing - changing data within a node Examples of Networks local, long distance telephone networks computer LANs: ethernet, token ring ARPANet/MILNET Cable TV networks Cellular The WANs phone networks INTERNET network definitions Networks computer network distributed LAN, network MAN, WAN integrated network internetwork/Internet network classification geographical coverage (LAN ... WAN) topology switching speed technique (data rates) data/information content geographical coverage LANs simpler, less software layers higher data transfer rates (generally) simple routing IEEE standards easily connected together via bridges examples: ethernet, token ring, FDDI geographical coverage MANs traditional cable TV, local phone DQDB, less category FDDI (?) used, as most networks can be classified into LAN/WAN geographical coverage WANs data speeds slower, in general (this distinction fading) national, international boundaries includes internetworking ARPANet much OSI first example more complex software model network topologies star ring bus fully connected tree mesh switching techniques broadcast no switching or routing; 1 station transmits, all others can receive collisions occur if more than 1 attempts to transmit at once examples: ethernet LAN and radio networks, satellites (to some degree) switching techniques circuit 3 switching distinct phases traditional voice network nice for user, but inefficient use of transmission facilities served traditional voice networks well, but gradually becoming outdated by new technology switching techniques message switching sends entire message as single transmission efficiency problems from unbound msg. size packet switching fixed packet size much more efficient use of facilities several refinements; fast packet switching (ATM) is culmination network model: ISO 7-layers designed ~1970; still heavily referenced 7 layer model for networks -1. physical - moves a bit from a to b using a physical(electrical, optical, etc.) signal 2. data link - groups bits into frames, or messages, for error control and information 3. network - routing function network model: ISO 7-layers 4. transport - end to end; interface between user apps and the network/internet 5. session, presentation - ?? 7. application - user interface to network, and user services: email, file transfer, world wide web, etc. network model: IEEE LAN model complements ISO model for LAN specific networks; more specific in data link, physical layers; other layers unchanged layers: physical MAC: media access control LLC: logical link control network model: DoD model Alternative view; viewed networks as basic building blocks, thus not included in model Fewer layers Applications host-host internet (transport; now TCP ) layer (now IP) network interface layer purposes of networks resource sharing increased reliability (redundancy, etc.) efficiency communications future applications: voice, video, data, images, appliances, .... ? basic network services e-mail file transfers (ftp, etc) remote login (rlogin, telnet) WWW (web) network ing industry historically two separate and very different industries -- computers and communications computer industry: IBM, DEC, Sun, Apple, Cray, SGI, Compaq, Dell, Gateway, Microsoft, etc communications: AT&T, Sprint, MCIWorldCom, RBOCs, GTE, other phone companies, etc. network ing industry these 2 industries have been merging signs of the merging initial purpose of each signals importance of each to the other research labs Sun’s logo “the network is the computer” industry sectors Computer Industry mainframes, “big” computers - IBM, Cray mid-size, workstations - Sun, SGI, (DEC, Tandem) personal computers (manufacurers) Compaq, Dell, Gateway PCs - software - Microsoft semiconductors for PCs - Intel, AMD, NSM industry sectors Communications long distance telephone (ATT, Sprint) local telephone (Pacific Bell, etc.) telecom. equipment (Lucent, Nor. Telecom) telco eqmt (Lucent, etc.) data; internet (Cisco, 3Com) internet radio, service providers (AOL, etc) wireless data, satelite, etc standards for networks reasons for standards advantages disadvantages standards organizations communication protocols protocol: the algorithm or procedure used for communication between processes at the same layer examples: telephone call; e-mail protocol processes make use of lower layers as a service. heart of communications process communication protocols some bit things protocols do interpretation to signals group error bits into messages detection and correction synchronization make more efficient use of networks facilities communication protocols three basic phases of data communications 1. connection establishment 2. data transfer 3. connection termination connection-oriented/connectionless