Computer Networking


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Computer Networking

  1. 1. INF4/MSc Computer Networking Lecture 1: Introduction & Overview D K Arvind dka AT IF 2.18
  2. 2. We will look at: – Network architecture principles » From signals and wires to protocols – Architecture of the Internet – Wireless networks » LANs, personal area, wide/metropolitan area 2
  3. 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, 2003 3.Data and Computer Communications (7e), William Stallings. Prentice Hall, 2003 • News on developments on comp. networking 3
  4. 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. 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.Essay on convergence in telecommunication networks 2.Technical report based on a survey of papers • Plagiarism: don’t do it! – Read the relevant informatics and university web pages 5
  6. 6. Course admin • Lecturers: DK Arvind & Mahesh Marina • Two lectures / week – 10am Mon, WRB G.04 – 10am Thu, WRB G.04 • Course web page: • Newsgroup: eduni.inf.ug4 Contact: dka AT the usual address 6
  7. 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. 8. Interdependencies, Interdependencies,… FASB; IRC e-commerce, Trading, transfers IT Banking & Finance Regulations & enforcement Currency (US Treasury; FERC; DOE Federal Reserve ) Communications Communications Communications Communications Communications Communications E e-government, L IT Government Detection, 1st responders, Personnel/Equipment E repair (Military) T Medical C equipment FEMA; DOT E Financing, regulations, & enforcement Financing, regulations, & enforcement Financing, regulations, & enforcement Financing, regulations, & enforcement Financing, regulations, & enforcement Financing, regulations, & enforcement Emergency Response T Fire Location, EM L suppression contact R Signalization, E switches, DOT I control systems Transportation C Communications Communications Communications Communications Communications SCADA C O Storage, I pumps, DOE; DOT M control systems, Oil & Natural Gas T compressors Water for production, cooling, SCADA Y Water for cooling, emissions control emissions control EPA Potable & Waste Water SCADA Pumps, lifts, control systems Cooling Switches, control systems 8 Source: Miriam Heller
  9. 9. The Plant: A Complex Environment Plant Other Servers Computing Devices hours Business Management min Personal Computer Network Manager Archive Replay Module Area ServersPlant Control Stations secs Network Application History Additional CN Modules Modules Module Module Fiber Optics 1 sec Process Management Network Network PLC Gateway msec Gateway Subnetwork Gateway Network Interface Gateway Control Networ Other Data Module PLC Other Extenders Hiway Boxes Subsystems Multifunction CON k Logic Manager or Controller Process etw μ sec Extended Manager TRO bn Controller Su L NE Basic Advanced Controller Process TWO Advanced Field Management Manager Multifunction RK LocalProcessors Controller Transmitters Smartine Source: TRUST Transmitters 9
  10. 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, voicemail, electronic banking, ,… – Computer networks enable email, information search, electronic commerce, … • Value of the network depends on its size: the larger, the better – What’s the use of email if only a few people use it? 10
  11. 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. 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. 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 t0 t1 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. 14. The N2 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. 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 A b α A β c d γ Metropolitan National 15
  16. 16. Internetworks net 3 G = gateway G net 1 G G G net 5 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. 17. Addressing Addressing required to identify source and destination end- points – 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. 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. 19. Factors in Communication Network Evolution Technology, Regulation, Markets, Standards Can it be built? Will it inter-operate? Technology Standards Will it sell? Is it allowed? Regulation Market – 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. 20. Computer network uses • Resource sharing – Printers, disks, specialised hardware, … • Information sharing – Database access • Human communication – Email, 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. 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 Multiple technologies overlap Technical Expert Time 21
  22. 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. 23. Market – Usefulness of a service often depends on there being a critical mass of subscribers e.g. email, 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. 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