Connections

A connection is an instance of communication link between two processes. Each connection is specified by a unique 5-tuple, called a association:

1. Protocol (e.g., tcp, udp)
2. Local Address (Net ID + Host ID)
3. Local Process (Port Number)
4. Foreign Address (Net ID + Host ID)
5. Foreign Process (Port Number)

For instance,

{ tcp, 128.10.9.3, 1500, 128.10.0.7, 21 }

One half of an association is called a socket. An association is thus a 3-tuple (the protocol is duplicated in a socket pair).