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IP: Connectionless Datagram Delivery
IP data transfer across an internet is based on three fundamental
principles:
- Unreliable delivery
- delivery of data is not guaranteed. A packet of data may be
lost in the network, may be duplicated (ie: delivered twice) or may
be delivered out of order. The IP service will not detect such
conditions, nor will it notify the sender or receiver if they
occur.
- Connectionless delivery
- each packet is treated entirely indpendently of all others. No
information is kept as to which packets have been forwarded, and
packets may travel over different routes to the same
destination.
- Best-Effort delivery
- the packet delivery mechanism is engineered to always deliver
packets if possible. It will not gratuitously drop packets:
unreliability should only occur when underlying resources (eg
buffer space) are exhausted.
These specifications allow the IP service to concentrate on its
job: delivering packets. As we have seen, higher level protocols
(usually TCP) transform the IP service into a reliable, sequenced
interprocess communications mechanism
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