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Glossary
PRI
Primary Rate Interface: A type of ISDN connection between a PBX and
a long-distance carrier, which is made up of a single 64Kbps D channel in
addition to 23 (T-1) or 30 (E-1) B channels. See also: ISDN.
priority queueing
A routing function in which frames temporarily placed
in an interface output queue are assigned priorities based on traits such as
packet size or type of interface.
privileged mode
Command-line EXEC mode used in Cisco routers and
switches that provides both viewing and changing of configurations.
process/application layer
Upper layer in the Internet Protocol stack.
Responsible for network services.
process switching
As a packet arrives on a router to be forwarded, it's
copied to the router's process buffer, and the router performs a lookup on the
layer-3 address. Using the route table, an exit interface is associated with
the destination address. The processor forwards the packet with the added
new information to the exit interface, while the router initializes the fast-
switching cache. Subsequent packets bound for the same destination address
follow the same path as the first packet.
PROM
programmable read-only memory: ROM that is programmable
only once, using special equipment. Compare with: EPROM.
propagation delay
The time it takes data to traverse a network from its
source to its destination.
protocol
In networking, the specification of a set of rules for a particular
type of communication. The term is also used to refer to the software that
implements a protocol.
protocol stack
A collection of related protocols.
pruning
The act of trimming down the shortest-path tree. This deactivates
interfaces that do not have group participants.
Proxy Address Resolution Protocol
Proxy ARP: Used to allow redun-
dancy in case of a failure with the configured default gateway on a host.
Proxy ARP is a variation of the ARP protocol in which an intermediate
device, such as a router, sends an ARP response on behalf of an end node
to the requesting host.
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