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

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Presentation on theme: "IP datagrams Service paradigm, IP datagrams, routing, encapsulation, fragmentation and reassembly."— Presentation transcript:

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


10 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

11 Fragmentation A datagram that is larger than MTU is fragmented into smaller datagrams

12 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

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

14 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

15 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

16 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

17 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

18 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

19 Writing down IPv6 addresses Replaces dotted decimal notation with more compact colon hexadecimal 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

20 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

21 Base Header

22 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

23 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

24 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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