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is the common modem connection used for Internet dial−up.
Point−To−Point Tunneling Protocol (PPTP)
A protocol that encapsulates private network data in IP packets. These packets are transmitted over
synchronous and asynchronous circuits to hide the underlying routing and switching infrastructure of
the Internet from both senders and receivers.
polling
The media−access method for transmitting data, in which a controlling device is used to contact each
node to determine if it has data to send.
Port Adapter Modules
Modules attached to the Carrier Access Modules on the LS1010 ATM and Catalyst 5500 series ATM
bus that provide physical ATM line ports for the end−user stations.
Port Aggregation Protocol (PAgP)
Manages the Fast EtherChannel bundles and aids in the automatic creation of Fast EtherChannel
links.
PortFast
A protocol that forces an STP port to enter the forwarding state immediately after startup for a single
workstation or server connected to a switch port.
power on self test (POST)
A series of tests run on a Cisco Catalyst switch when the power is turned on. POST tests the
hardware, memory, processors, ports, and ASICs to verify they are functioning properly.
Presentation layer
Layer 6 of the OSI Reference Model. This layer prepares information to be used by the Application
layer.
Primary Rate Interface (PRI)
A higher−level network interface standard for use with ISDN. Defined at the rate of 1.544Mbps, it
consists of a single 64Kbps D channel plus 23 (T1) or 30 (E1) B channels for voice or data.
Private Virtual Circuit (PVC)
A logical connection between locations through a Frame Relay and ATM cloud. When a company has
three branch offices, and each location physically connects to the Frame Relay provider's network
cloud through a series of switches, it appears to the end users as if the three branch offices are directly
connected to the local network. (Not to be confused with a Permanent Virtual Circuit, also known as a
PVC.)
proprietary
A standard or specification that is created by a manufacturer, vendor, or other private enterprise and is
not always a recognized standard.
Proprietary Fat Pipe ASIC (PFPA)
An ASIC utilized on the Catalyst 3000 series switches that use no 10BaseT ports such as Fast
Ethernet, 100VG/AnyLAN, ATM, or the Stackport of the Stack Port Matrix. Functionally, the PFPA
is the same as the LMA.
protocol
A set of rules that govern network communications between networks, computers, peripherals, and
operating systems.
Protocol Identification field
In a frame, a five−byte field used to identify to the destination node the protocol that is being used in
the data transmission.
protocol stack
Two or more protocols that work together, such as TCP and IP or IPX and SPX. Also known as a
protocol suite.
Proxy ARP
Used by end−stations to discover the IP address of the default gateway. The end−stations dynamically
acquire the IP and MAC address of the default gateway. The IP address of the default gateway is
manually configured on the node running Proxy ARP.
Public Switched Telephone Network (PSTN)
All the telephone networks and services in the world. The same as POTS, PSTN refers to the world's
collection of interconnected public telephone networks that are both commercial and government
owned. PSTN is a digital network, with the exception of the connection between local exchanges and
389
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Troubleshooting
