Networking Glossary
- protocol A formal description of messages to be exchanged and rules to be followed for two or more systems to exchange information. [Source: RFC 1208]
- PCI (Protocol Control Information) The protocol information added by an OSI entity to the service data unit passed down from the layer above, all together forming a Protocol Data Unit (PDU). [Source: RFC 1208]
- PDU (Protocol Data Unit) This is OSI terminology for "packet." A PDU is a data object exchanged by protocol machines (entities) within a given layer. PDUs consist of both Protocol Control Information (PCI) and user data. [Source: RFC 1208]
- proxy The mechanism whereby one system "fronts for" another system in responding to protocol requests. Proxy systems are used in network management to avoid having to implement full protocol stacks in simple devices, such as modems. [Source: RFC 1208]
- PSN The modern term used for nodes in the ARPANET and MILNET. These used to be called IMPs (Interface Message Processors). PSNs are currently implemented with BBN C30 or C300 minicomputers. [Source: RFC 1208]
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