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Glossary

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polling

The procedure of orderly inquiry, used by a primary network

mechanism, to determine if secondary devices have data to transmit. A mes-
sage is sent to each secondary, granting the secondary the right to transmit.

POP

1) point of presence: The physical location where an interexchange

carrier has placed equipment to interconnect with a local exchange carrier.
2) Post Office Protocol (currently at version 3) A protocol used by client
e-mail applications for recovery of mail from a mail server.

port security

Used with layer-2 switches to provide some security. Not

typically used in production because it is difficult to manage. Allows only
certain frames to traverse administrator-assigned segments.

port numbers

Used at the transport layer with TCP to keep track of host-

to-host virtual circuits.

positive acknowledgment with retransmission

A connection-oriented

session that provides acknowledgment and retransmission of the data if it is
not acknowledged by the receiving host within a certain time frame.

POTS

plain old telephone service: This refers to the traditional analog

phone service that is found in most installations.

PPP

Point-to-Point Protocol: The protocol most commonly used for dial-

up Internet access, superseding the earlier SLIP. Its features include address
notification, authentication via CHAP or PAP, support for multiple proto-
cols, and link monitoring. PPP has two layers: the Link Control Protocol
(LCP) establishes, configures, and tests a link; and then any of various Net-
work Control Programs (NCPs) transport traffic for a specific protocol suite,
such as IPX. See also: CHAP, PAP, and SLIP.

prefix routing

Method of defining how many bits are used in a subnet and

how this information is sent in a routing update. For example, RIP version
1 does not send subnet mask information in the route updates. However, RIP
version 2 does. This means that RIP v2 updates will send /24, /25, /26, etc.,
with a route update, which RIP v1 will not.

Presentation layer

Layer 6 of the OSI reference model, it defines how

data is formatted, presented, encoded, and converted for use by software at
the Application layer. See also: Application layer, Data Link layer, Network
layer, Physical layer, Session layer, and Transport layer.

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