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IP datagrams

IP datagrams. Service paradigm, IP datagrams, routing, encapsulation, fragmentation and reassembly. Internet service paradigm. TCP/IP supports both connectionless and connection-oriented services fundamental delivery service is connectionless at the Internet layer

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IP datagrams

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  1. IP datagrams Service paradigm, IP datagrams, routing, encapsulation, fragmentation and reassembly

  2. Internet service paradigm • TCP/IP supports both connectionless and connection-oriented services • fundamental delivery service is connectionless at the Internet layer • optional reliable connection-oriented service is layered on top of this at the transport layer

  3. IP datagrams • Packets of data are sent across multiple physical networks via routers • Internet protocols define a universal virtual packet - the IP datagram • The amount of data carried in a datagram is not fixed and is determined by an application

  4. Routers and routing tables • Each router forwards a virtual packet by using a local routing table • Each entry is: • destination address • mask • next hop • IP address of a router or • Deliver direct • Then does address resolution

  5. Example routing table

  6. Best-effort delivery • IP attempts best effort delivery and does not guarantee to deal with: • datagram duplication • delayed or out of order delivery • corruption of data • datagram loss • These issues are dealt with other protocol layers

  7. IP datagram header format

  8. Encapsulation • When an IP datagram is sent across a physical network it is placed in the data area of a frame and the frame type is set to IP

  9. MTU and datagram size • Maximum transmission unit - max of data that a frame can carry on a given network • A packet may have to cope with different MTU sizes as is passes over an internet

  10. Fragmentation • A datagram that is larger than MTU is fragmented into smaller datagrams

  11. Reassembly • Is done at the final host • routers require less state information • fragments can take different routes • Header fields indicate when the data is a fragment and also where it belongs • Whole datagram is lost if any fragment is lost

  12. The Future of IP (IPv6) Motivation for IPv6, Addressing, Datagram Format, Paths

  13. Motivation • IP has been extremely successful at coping with the expansion of The Internet and changes in network hardware over 20 years! • However: • limited address space will soon run out • new application requirements • real-time audio and video require guaranteed service • collaboration technologies require ways of sending packets to groups of hosts

  14. What is in a name? • The current IP is IPv4 • The new version was originally called IP - The Next Generation (IPng), but this became associated with several proposals • The final proposal is called IPv6

  15. Key features of IPv6 • Connectionless like IPv4 • 128 bit address size • Different addressing modes: unicast, multicast and cluster • Extension headers • Support for audio and video

  16. Three types of address • unicast - address corresponding to a single computer. Datagram sent along shortest path • multicast - • address corresponding to a set of computers, • members can change at any time. • one copy of a datagram is delivered to each • only one copy passes over intervening networks • used for collaborative applications

  17. Cluster • address corresponds to a set of computers that share a common prefix • a datagram is delivered to one of these • used for replicating a service

  18. Writing down IPv6 addresses • Replaces dotted decimal notation with more compact colon hexadecimal 105.220.136.100.255.255.255.255.0.0.18.128.140.10.255.255=> 69DC:8864:FFFF:FFFF:0:1280:8C0A:FFFF • Zero compression further reduces space FF0C:0:0:0:0:0:0:B1 => FF0C::B1 • Especially useful because an IPv6 address that begins with 96 zeros contains an IPv4 address in the last 32 bits

  19. Datagram format • Datagram format includes a base header and optional extension headers • saves space - a typical application will only use a few IPv6 facilities • the protocol can be extended to support new features without being redesigned

  20. Base Header

  21. Paths • Applications can be used to set up network paths in advance • These can be associated with different traffic classes that provide different Quality of Service (QoS) • Necessary for real-time audio and video

  22. Examples of Collaborative Applications • 􀁺 Collaborative Virtual Environments (CVEs) • Shared 3D virtual world • Each user controls own viewpoint • Interaction with objects • Users represented by avatars • Communication through embedded audio, video, text and graphical gestures

  23. CVE and network traffic • In a CVE each user may be an active sender as well as a receiver of various kinds of information • Many users may send data at the same time • There may be hundreds of users • As a result, CVEs can generate large volumes of network traffic

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