Glossary Terms - P


ping (Packet internet groper)
A program used to test reachability of destinations by sending them an ICMP echo request and waiting for a reply. The term is used as a verb: "Ping host X to see if it is up!" [Source: RFC 1208]
proxy ARP (Packet Switch Node)
The technique in which one machine, usually a router, answers ARP requests intended for another machine. By "faking" its identity, the router accepts responsibility for routing packets to the "real" destination. Proxy ARP allows a site to use a single IP address with two physical networks. Subnetting would normally be a better solution. [Source: RFC 1208]
Physical Layer (Physical Layer)
The OSI layer that provides the means to activate and use physical connections for bit transmission. In plain terms, the Physical Layer provides the procedures for transferring a single bit across a Physical Media. [Source: RFC 1208]
Physical Media (Physical Media)
Any means in the physical world for transferring signals between OSI systems. Considered to be outside the OSI Model, and therefore sometimes referred to as "Layer 0." The physical connector to the media can be considered as defining the bottom interface of the Physical Layer, i.e., the bottom of the OSI Reference Model. [Source: RFC 1208]
PPP (Point-to-Point Protocol)
The successor to SLIP, PPP provides router-to-router and host-to-network connections over both synchronous and asynchronous circuits. See SLIP. [Source: RFC 1208]
port (port)
The abstraction used by Internet transport protocols to distinguish among multiple simultaneous connections to a single destination host. See selector. [Source: RFC 1208]
Presentation Address (Presentation Address)
See OSI Presentation Address. [Source: RFC 1208]
Presentation Layer (Presentation Layer)
The OSI layer that determines how Application information is represented (i.e., encoded) while in transit between two end systems. [Source: RFC 1208]
PRMD (Private Management Domain)
An X.400 Message Handling System private organization mail system. Example: NASAmail. See ADMD. [Source: RFC 1208]
POSI (Promoting Conference for OSI)
The OSI "800-pound gorilla" in Japan. Consists of executives from the six major Japanese computer manufacturers and Nippon Telephone and Telegraph. They set policies and commit resources to promote OSI. [Source: RFC 1208]
protocol (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 (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 (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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