Lecture 1: Introduction & Overview

Transcription

1 INF4/MSc Computer Networking Lecture 1: Introduction & Overview Aris Efthymiou aefthymi AT inf.ed.ac.uk JCMB 1420 Computer Networking, Copyright University of Edinburgh 2005 This course is an introduction to computer networking We will look at: Network architecture basics Two important architectures Wireless networks 2 1

2 Recommended Reading Much of the course is based on the textbook: Computer Networking: A top-down approach featuring the Internet, (3/e) J. Kurose & K. Ross, Addison-Wesley, 2005 Many other good books: 1.Communication Networks (2e), Leon-arcia & Widjaja. Mcraw Hill, 2004!"#$%&! 2.Computer Networks (4e), Andrew S. Tanenbaum. Prentice Hall, Data and Computer Communications (7e), William Stallings. Prentice Hall, 2003 News on developments on comp. networking (esp for the MSc students) 3 Learning Outcomes Knowledge of key concepts, protocols and algorithms in networking An understanding of the complexity of networks, their structure and utility The ability to apply knowledge to networking applications, to network infrastructure and to network management The ability to write and present clear and concise description of complex issues Additionally, for the MSc version: An insight into likely future developments in the field of networking 4 2

3 Assessment 75% of course mark Final exam Past papers available from the School archive 25% of course mark INF4 - Two coursework assignments, equally weighted MSc - Three coursework assignments, equally weighted Coursework (look web page for dates, etc) 1.Implementation of a routing algorithm in Java 2.Technical report (~5 pages) on an advanced networking topic 3.Essay on future of networking (MSc only) Plagiarism: don t do it! Read the relevant informatics and university web pages 5 Course admin Two lectures / week 10am Mon, Darwin Building,.10 10am Thu, Ashworth Building, Theatre 3 No lectures in week 6, disruptions likely in early November But coursework is still on Week 11 will be used for catching up on lectures, if needed Course web page: No tutorials No slides hardcopies Office hours: Thursdays 11-12, JCMB 1420 Contact: aefthymi AT the usual address 6 3

4 Service-oriented view of computer networks A computer network provides a communication service, i.e. enables the exchange of information between computers (and their users) that are located at various geographical locations Communication service is ubiquitous and an essential infrastructure of modern society Comparable in value with transportation, water, electricity, Because there are no limits to information, networking enables further services For example the telephone network enables fax, voic , electronic banking,, Computer networks enable , information search, electronic commerce, Value of the network depends on its size: the larger, the better What s the use of if only a few people use it? 7 Characteristics of the communicated information Non-interactive: Text, pictures, music, video Two sub-categories: streaming or not ' Interactive: Teleconferencing, videoconferencing, instant msg/chating Size is an important factor Compression (lossy/lossless) can help, opens up a computation vs communication trade-off Worst case: Musicians playing instruments together through the network Requires low latency, high-throughput (for quality sound), low jitter 8 4

5 Characteristics of the communication services Connection-oriented (think telephone) Receiver is active while information is transmitted Must establish connection, before any data is transmitted Connectionless (think [e]mail) Data transmission can start earlier Other service characteristics: Confirmed unconfirmed delivery Quality of service characteristics: () *+,-., 9 Approaches to Network Design Networks provide connectivity between users at the network edge through a transmission system, the network core Using various types of physical media (wires, radio, optical fibre, etc.) and devices (switches, routers, multiplexers, etc.) Network core equipment is fundamentally different to equipment at the network edge t 0 Network t1 Cost-effective design necessary to meet user requirements Networks usually designed to carry specific types of information Voice, TV, bits, characters etc. 10 5

6 The N 2 Problem Pairwise interconnections would require N*(N-1) links or a central switching access network, and just N access links Networks consist of point-to-point links interconnected by switches for a multi-hop path, routing decides which path to take at a switch forwarding actually moves the data in the direction decided 11 Larger Networks Connections between local communities use trunks between local switches Multiplexers concentrate the traffic over the more expensive line Demultiplexers separate out the individual parts of the traffic for distribution Networks are hierarchical: Metropolitan networks interconnect access networks Regional networks connect metropolitan networks National networks, international networks etc. using backbone networks a b A α A β c d γ Metropolitan National 12 6

7 Internetworks net 1 net 3 net 5 = gateway net 2 net 4 Networks of networks The Internet Protocol (IP) was developed to provide connectionless transfer of packets across an internet The component networks are interconnected by packets switches called gateways or routers, which direct the transfer of packets IP provides a best-effort service i.e. it does its best to deliver a packet, but it does not guarantee successful delivery 13 Addressing Addressing required to identify source and destination endpoints Hierarchical addressing uses common prefixes for end-points in the same geographical areas /!0 (%! # Hierarchical addressing in Wide Area Networks e.g. the Internet Flat addressing in Local Area Networks e.g. ethernets 1!* 14 7

8 Switching Circuit-switching In early communication networks, switching was performed at the electrical signal level, creating a real circuit end to end In modern digital transmission media, circuit-switching means allocation of dedicated resources (e.g. a share of a link s transmission capacity) end to end Switches forward information one bit at a time (in theory) Packet/message switching Switches store whole packet and then forward it using the full link transmission capacity Connectionless or datagram." " Virtual circuit ""!1" 15 Factors in Communication Network Evolution Technology, Regulation, Markets, Standards Will it inter-operate? Technology Can it be built? Standards Is it allowed? Regulation Market Will it sell? Availability of a technology does not mean it will sell Never very clear beforehand whether a market exists for a product or service The move away from monopoly telecomms suppliers makes standards essential 16 8