Communication protocols in a network context

摘要

In a distributed computers network based on a packet-swltched communication subnet, it is possible to describe the system as a hierarchical structure. We will consider here only three levels:

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-level 0: communication between nodes of the subnets.

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-level 1: communication between hosts connected to the net.

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-level 2: communication between users processes (subscribers) in different hosts.

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At each level, the communication is based on a protocol and the data structures to be exchanged are different. For instance the data structure exchanged at level 2 may be a sequential file. As there is no direct support of communication at this level, it is through the mechanisms of level 1 and 0 that the transfer will take place with data structure at each level not directly related to the upper level one. The complete definition of the system will therefore required not only the level 0, 1 and 2 protocols, but also inter-level protocols.

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In the following, we will concentrate onthe level 1 protocol. It is the basic communication protocol of a network since it will be used by user processes in different hosts and it will use the subnet as a communication support. This level 1 entity is called a "TS" (transport station) in CYCLADES [13] and a "TCP" (transmission control program] in [2].