Service paradigm, IP datagrams, encapsulation, fragmentation and reassembly

 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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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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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

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

 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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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

 A datagram that is larger than MTU is fragmented into smaller datagrams

 Is done at the final host
 routers require less state information
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 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