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Published byKenya Glasco Modified over 10 years ago
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IP datagrams Service paradigm, IP datagrams, routing, encapsulation, fragmentation and reassembly
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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
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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
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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
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Example routing table
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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
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IP datagram header format
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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
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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
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Fragmentation A datagram that is larger than MTU is fragmented into smaller datagrams
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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
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The Future of IP (IPv6) Motivation for IPv6, Addressing, Datagram Format, Paths
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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
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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
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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
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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
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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
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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
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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
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Base Header
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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
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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
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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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