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Packet Delivery: The Network Service
Once the transport module has built a segment of data, it passes it
to a network service module, also normally
residing within the operating system.
The network service module builds a packet
containing the entire TPDU as its data part, and prefixes a network
header containing, among other information, the network address of
the destination computer. It then passes the packet to the actual
network for delivery.
In the Internet, the network service module implements the IP
protocol, and NPDUs are normally called IP packets
or datagrams.
Note that the network service need not guarantee reliable delivery
of packets -- why not?
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