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Connections. 3G next generation of mobile communications technology. other countries more fully utilize mobile phones. increased bandwidth, up to 384 kbps when a device is stationary or moving at pedestrian speed, 128 kbps in a car, and 5-10 mbps stationary. video, multimedia support.

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  1. Connections 3G • next generation of mobile communications technology. • other countries more fully utilize mobile phones. • increased bandwidth, up to 384 kbps when a device is stationary or moving at pedestrian speed, 128 kbps in a car, and 5-10 mbps stationary. • video, multimedia support.

  2. Approaches to Networking Client Server Model • server fulfils client requests • high speed, high capacity computer is the server • hierarchical structure, server is essential

  3. Approaches to Networking Peer 2 Peer Model • any computer can be a client or a server. • often used on smaller networks (but not necessarily, e.g. music sharing). • Windows & MacOS allow for P2P networking.

  4. Internet • global network of networks. • TCP / IP communication standard. • to communicate, networks must speak the same language.

  5. Internet Motivation • Researchers : share computing resources, very few computers, expensive. • Military : cold war, wanted a communication network.

  6. Military Needs • assume unreliability. • decentralized : all connected computers are equal. • most work when lines are broken, and nodes are down.

  7. Network Must • connect important government & research computers. • resist point-of-failure attacks : continue to operate even if a city on the network was destroyed. • be fault-tolerant : continue to operate even if something went wrong within the network – e.g., a computer crashed, or a transmission line was broken.

  8. Solution • designed to be a decentralized network of computers that could adapt the flow of traffic and to changes in the state of the overall system. • the way that information travels on the Internet is similar to the way that traffic moves on an interconnected system of roads and highways.

  9. Like a Highway • detours - if a road is flooded find an alternate route. • minimize the impact of a lost or delayed vehicle - instead of transporting groups of sixty people in buses, put each person on a motorcycle or alone in a car.

  10. Like a Highway • addressing - each person knows the exact address of their destination. • traffic reports - have check points at all intersections to reassess the best route based on current traffic conditions.

  11. Internet Protocol • Internet Protocol - works something like the postal system, it describes how to form and address online communication packages. • packets - messages sent over the Internet are broken into pieces equivalent to about 1500 characters.

  12. IP Addresses • every computer on the Internet has a unique address called an IP address. • valid IP addresses are in the form of dotted quads : four numbers, each in the range of 0 to 255, and separated by a period (e.g.

  13. IP Addresses every packet is addressed with : • the source IP address • (e.g. from: • the destination IP address • (e.g. to: • the packet number • (e.g. number: 10 of 16)

  14. Transmission Control Protocol • ensures the transmission and delivery of data from source to destination. • as packets arrive at routers or hosts (computers on the network), the routers decide the best path to send each packet on.

  15. Transmission Control Protocol • TCP describes how to put the packets back together (reassemble the message) once the packets reach their destination. • if a packet is lost or damaged (corrupted) along the way, TCP allows for a "retransmit" message to be sent asking for the missing or bad packet to be resent.

  16. Check Sums • check if packets may have been corrupted in transit. • apply some algorithm to add an extra number to the packet. • if, when the packet arrives, the same algorithm does not result in the same number being calculated, we know there was a data transmission error.

  17. TCP / IP • Transmission Control Protocol : • establishes a connection between two hosts. • guarantees delivery of data - packets will arrive in the order they were sent. • Internet Protocol : • forming and addressing packets.

  18. TCP / IP • Open Standard : • not owned by any one, made public. • advantage : anyone can design add-ons. • Disadvantage : duplicated by others. • Cross-Network Communication • Low Level Protocols – hidden from users.

  19. Packet-Switching • different paths • traffic gets through even when part of the network is down. • packets that have the same source and destination MAY still take different routes. • Router : chooses best path. • Switch : just forwards traffic, may be faster.

  20. Birth and Growth Labour Day, 1969, ARPANET is born and connects 4 host : - U of California at L.A. - U of California at Santa Barbara - U of Utah - Stanford Research Institute.

  21. Birth and Growth 1969 : 4 hosts connected. 1971 : 23 hosts connected. 1974 : 62 hosts connected. 1984 : more than 1000 hosts connected. 1987 : more than 10 000 hosts connected. 1989 : more than 100 000 hosts connected. 1992 : more than 1 000 000 hosts connected. ** doubling every year since mid 80's, slower now.

  22. How Big? • Changing too fast to measure. • decentralized – no one person controls and monitors the entire Internet. • no hard boundaries – difficult to say exactly who is connected.

  23. Connecting to the Internet Direct Connection Dialup Connection Broadband Connection

  24. Direct Connection • devoted link from your LAN to the closest point on the Internet (phone company, cable company, university). • computers on the LAN have IP addresses. • fast service, able to transfer large files quickly. • using T1, T3 or fiber optic.

  25. Dial-Up Connection • telephone lines and a modem. • email (files) stored on a host (server) and you connect to collect them. • Limited – not all traffic can be sent this way. • ISPs - Internet Service Providers. • various packages and services : email, web space, ect. • freenet – community access.

  26. Broadband Connection • higher bandwidth than typical modems. • speed can be comparable to a direct connection. • always connected. • DSL : phone company. • Cable Modem : cable company. • Wireless : Wi-Fi .

  27. Traffic Direction • Downstream – to your computer (download). • Upstream – to the Internet (upload).

  28. Internet & Web • the World Wide Web and the Internet are not the same thing. • WWW – an application of the Internet. • Popularity : • easy to use. • easy to add • easy to search.

  29. Internet Applications • email & mailing lists • FTP & file sharing • Usenet & boards & forums • World Wide Web • Instant Messaging & Chat • Remote Login & Telnet

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