Lecture 1: Introduction & Overview

Transcription

1 INF4/MSc Computer Networking Lecture 1: Introduction & Overview D K Arvind dka AT inf.ed.ac.uk JCMB 1504

2 This course is an introduction to computer networking We will look at: Network architecture basics» From signals and wires to protocols Two important architectures»internet» Asynchronous Transfer Mode Wireless networks» LANs, personal area, wide/metropolitan area 2

3 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-Garcia & Widjaja. McGraw Hill, 2004 Last year s book. Still OK, if you got it second hand, or from the library 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 3

4 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 An insight into likely future developments in the field of networking 4

5 Assessment 75% of course mark Final exam Past papers available from the School archive 25% of course mark Two coursework assignments, equally weighted Coursework (look web page for dates, etc) 1.Technical report on an advanced networking topic 2.Essay on future of networking Plagiarism: don t do it! Read the relevant informatics and university web pages 5

6 Course admin Two lectures / week 10am Mon, DHT am Thu, DHT 4.01 Course web page: No tutorials Newsgroup: eduni.inf.ug4 Contact: dka AT the usual address 6

7 Networked Critical Infrastructure A modern state has a network of control systems for the measurement and change of the infrastructure state for safe, uninterrupted, and efficient delivery of utilities (electricity, water), of services (telecommunication, health, transportation, banking), and of essential commodity (gas, oil) A network of distributed sensors for collecting data and software for extracting and interpreting information to raise the security of the critical infrastructure 7

8 Communications Communications Interdependencies, Interdependencies, FASB; IRC E L E C T R I C I T Y e-commerce, IT Regulations & enforcement FERC; DOE e-government, IT Detection, 1 st responders, repair Medical equipment Signalization, switches, control systems Storage, pumps, control systems, compressors Water for cooling, emissions control Pumps, lifts, control systems Fire suppression Banking & Finance Currency (US Treasury; Federal Reserve ) Government Personnel/Equipment (Military) Emergency Response Transportation Oil & Natural Gas Potable & Waste Water Switches, control systems Water for production, cooling, emissions control Trading, transfers FEMA; DOT Location, EM contact DOT SCADA DOE; DOT SCADA EPA SCADA Communications Communications Financing, regulations, & enforcement Cooling Source: Miriam Heller T E L E C O M 8

9 The Plant: A Complex Environment hours min secs Plant Servers Area Servers Plant Network Modules Business Management Personal Computer Network Manager Control Stations Application Module Other Computing Devices History Module Archive Replay Module Additional CN Modules 1 sec msec μ sec Network Gateway LocalProcessors Network Gateway ource: TRUST Subnetwork Process Management Subnetwork Gateway Other Data Hiway Boxes Multifunction Controller Extended Controller Basic Controller Advanced Multifunction Controller Transmitters Network Interface Module Field Management CONTROL NETWORK PLC Gateway PLC Logic Manager Process Manager Advanced Process Manager Fiber Optics Control Networ Other Extenders Subsystems Smartine Transmitters 9

10 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? 10

11 Characteristics of the communicated information Non-interactive: Text, pictures, music, video Two sub-categories: streaming or not» jitter is most important for streaming multimedia 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 11

12 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:» Performance (delay, throughput, delay-variation )» Error rate, security, 12

13 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 t 1 Network Cost-effective design necessary to meet user requirements Networks usually designed to carry specific types of information Voice, TV, bits, characters etc. 13

14 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 14

15 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 c A d β γ Metropolitan National 15

16 Internetworks net 1 G G net 3 G G net 5 G = gateway net 2 G net 4 G 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 16

17 Addressing Addressing required to identify source and destination endpoints Hierarchical addressing uses common prefixes for end-points in the same geographical areas» Facilitates routing» As in a postal address: country, county, town, district, street, number; the Post Office batches mail for countries and for towns, districts, streets etc. Hierarchical addressing in Wide Area Networks e.g. the Internet» Also facilitates routing Flat addressing in Local Area Networks e.g. ethernets» Adequate for the typically small number of local area end-points 17

18 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» Each packet/message routed independently of all other packets Virtual circuit» A route set up through switches and links in the network» All subsequent packets forwarded along the same path 18

19 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 19

20 Computer network uses Resource sharing Printers, disks, specialised hardware, Information sharing Database access Human communication , Voice-over-IP, file-sharing (pictures, music, ) Commerce Shopping on-line, banking, Entertainment Movies, games Remote access/monitoring/working Users of the network Computers Humans: experts, general public 20

21 Technology Limited by fundamental physical laws In most cases substantial opportunities for improvement remain Key technologies Transmission systems Computer processing capacity (Moore s Law) Cumulative Experience Professional Manager Entrepreneur Technical Expert Multiple technologies overlap Time 21

22 Regulation Telecomms services have always been government regulated» until very recently as state monopolies Deregulation and privatisation of monopolies» more competition in long distance telecomms» cable television and satellite broadcasting competition to terrestrial Radio spectrum allocation» has always been closely controlled nationally and internationally» cellular telephone frequencies, 900MHz and 1800 MHz allocations» 3G spectrum auctions Office of Communications (Ofcom) in the UK» promoting consumer interest» maintaining effective competition» ensuring services to meet all reasonable demands e.g. emergency services, directory information, rural services etc. 22

23 Market Usefulness of a service often depends on there being a critical mass of subscribers e.g. , SMS Economies of scale often vital to sustain services and develop new ones» cable and satellite TV» mobile phones Entrepreneurs always searching for the next Killer App» SMS messaging on mobile phones a success»wap a failure 23

24 Standards Agreements, industry-wide, with national and international scope Ensure interoperability of equipment made by different vendors» competition reduces prices Physical standards such as plugs and sockets e.g. USB Usage standards such as communications protocols» whether implemented by software or hardware Can arise initially as de facto standards from a successful product» e.g. ethernet» internationally standardised later or developed by subcommittees of standards bodies» Internet Engineering Task Force (IETF)» Institute for Electrical and Electronics Engineers (IEEE)» International Telecommunications Union (ITU)» International Standards Organisation (ISO) 24