Browsing: P
|
|
|
pacing |
See
flow
control.
|
|
packet |
Logical grouping of
information that includes a header containing control
information and (usually) user data. Packets are most
often used to refer to network layer units of data. The
terms
datagram,
frame,
message,
and
segment
are also used to describe logical information
groupings at various layers of the OSI reference model and
in various technology circles. See also
PDU.
|
|
packet assembler/disassembler |
See
PAD.
|
|
packet buffer |
See
buffer.
|
|
packet internet groper |
See
ping.
|
|
packet level protocol |
See
PLP.
|
|
packet line card |
See
PLC.
|
|
packet switch |
WAN device that routes
packets along the most efficient path and allows a
communications channel to be shared by multiple
connections. Sometimes referred to as a packet switch
node (PSN), and formerly called an IMP. See
also
IMP.
|
| packet-switched data network |
See
PSN.
|
| packet-switched network |
See
PSN.
|
| packet
switching |
Networking method in which
nodes share bandwidth with each other by sending packets.
Compare with
circuit
switching and
message
switching. See also
PSN
(packet-switched network).
|
| packet switch exchange |
See
PSE.
|
| packet-switching node |
See
PSN.
|
| PAD |
Packet assembler/disassembler.
Device used to connect simple devices (like character-mode
terminals) that do not support the full functionality of a
particular protocol to a network. PADs buffer data and
assemble and disassemble packets sent to such end devices.
|
|
paddle card |
See
access
card.
|
| Palo Alto Research Center |
See
PARC.
|
| PAM |
Pulse amplitude
modulation. Modulation scheme where the
modulating wave is caused to modulate the amplitude of a
pulse stream. Compare with
AM
and
FM.
See also
modulation.
|
| PAP |
Password
Authentication Protocol. Authentication protocol
that allows PPP peers to authenticate one another. The
remote router attempting to connect to the local router is
required to send an authentication request. Unlike CHAP,
PAP passes the password and host name or username in the
clear (unencrypted). PAP does not itself prevent
unauthorized access, but merely identifies the remote end.
The router or access server then determines if that user
is allowed access. PAP is supported only on PPP lines.
Compare with
CHAP.
|
| parallel
channel |
Channel that uses bus and
tag cables as a transmission medium. Compare with
ESCON
channel. See also
bus
and tag channel.
|
| parallelism |
Indicates that multiple
paths exist between two points in a network. These paths
might be of equal or unequal cost. Parallelism is often a
network design goal: if one path fails, there is
redundancy in the network to ensure that an alternate path
to the same point exists.
|
| parallel
transmission |
Method of data transmission
in which the bits of a data character are transmitted
simultaneously over a number of channels. Compare with
serial
transmission.
|
| PARC |
Palo Alto Research
Center. Research and development center operated
by XEROX. A number of widely-used technologies were
originally conceived at PARC, including the first personal
computers and LANs.
|
| PARC Universal Protocol |
See
PUP.
|
| parity check |
Process for checking the
integrity of a character. A parity check involves
appending a bit that makes the total number of binary 1
digits in a character or word (excluding the parity bit)
either odd (for odd parity) or even (for even
parity).
|
| partial
mesh |
Term describing a network in
which devices are organized in a mesh topology, with some
network nodes organized in a full mesh, but with others
that are only connected to one or two other nodes in the
network. A partial mesh does not provide the level of
redundancy of a full mesh topology, but is less expensive
to implement. Partial mesh topologies are generally used
in the peripheral networks that connect to a fully meshed
backbone. See also
full
mesh and
mesh.
|
|
Passive interface |
A
passive interface receives updates, but does not send them. It is
used to control routing update. The
passive-interface
command can be used with all IP interior gateway protocols. That is
that it can be use with RIP, IGRP, EIGRP, OSPF, and IS-IS.
|
| Password Authentication
Protocol |
See
PAP.
|
| patch panel |
An assembly of pin locations
and ports which can be mounted on a rack or wall bracket
in the wiring closet. Patch panels act like switchboards
that connect workstations cables to each other and to the
outside.
|
| path
control layer |
Layer 3 in the
SNA
architectural model. This layer performs sequencing
services related to proper data reassembly. The path
control layer is also responsible for routing. Corresponds
roughly with the
network
layer of the OSI model. See also
data
flow control layer,
data
link control layer,
physical
control layer,
presentation
services layer,
transaction
services layer, and
transmission
control layer.
|
|
path control network |
SNA concept that consists of
lower-level components that control the routing and data
flow through an SNA network and handle physical data
transmission between SNA nodes. Compare with
NAU.
|
| path cost |
See
cost.
|
| path name |
Full name of a UNIX, DOS, or
LynxOS file or directory, including all directory and
subdirectory names. Consecutive names in a path name are
typically separated by a forward slash (/) or a backslash
(\), as in /usr/app/base/config.
|
| payload |
Portion of a frame that
contains upper-layer information (data).
|
| PBX |
Private branch
exchange. Digital or analog telephone switchboard
located on the subscriber premises and used to connect
private and public telephone networks.
|
| PCI |
Protocol control
information. Control information added to user
data to comprise an OSI packet. The OSI equivalent of the
term header. See also
header.
|
| PCM |
Pulse code
modulation. Transmission of analog information in
digital form through sampling and encoding the samples
with a fixed number of bits.
|
| PCR |
Peak cell rate.
Parameter defined by the ATM Forum for ATM traffic
management. In CBR transmissions, PCR determines how often
data samples are sent. In ABR transmissions, PCR
determines the maximum value of the ACR. See also
ABR
(available bit rate),
ACR,
and
CBR.
|
| PDN |
Public data network.
Network operated either by a government (as in Europe) or
by a private concern to provide computer communications to
the public, usually for a fee. PDNs enable small
organizations to create a WAN without all the equipment
costs of long-distance circuits.
|
| PDU |
Protocol data unit.
OSI term for packet. See also
BPDU
and
packet.
|
| peak cell rate |
See
PCR.
|
| peak rate |
Maximum rate, in kilobits
per second, at which a virtual circuit can transmit.
|
| peer-to-peer
computing |
Peer-to-peer computing calls
for each network device to run both client and server
portions of an application. Also describes communication
between implementations of the same OSI reference model
layer in two different network devices. Compare with
client-server
computing.
|
| performance
management |
One of five categories of
network management defined by ISO for management of OSI
networks. Performance management subsystems are
responsible for analyzing and controlling network
performance including network throughput and error rates.
See also
accounting
management,
configuration
management,
fault
management, and
security
management.
|
| peripheral node |
In SNA, a node that uses
local addresses and is therefore not affected by changes
to network addresses. Peripheral nodes require boundary
function assistance from an adjacent subarea node.
|
| permanent virtual circuit |
See
PVC.
|
| permanent virtual connection |
See
PVC.
|
| permanent virtual path |
See
PVP.
|
| permit processing |
See
traffic
policing.
|
| P/F |
Poll/final bit.
Bit in bit-synchronous data link layer protocols that
indicates the function of a frame. If the frame is a
command, a 1 in this bit indicates a poll. If the frame is
a response, a 1 in this bit indicates that the current
frame is the last frame in the response.
|
| PGP |
Pretty Good Privacy.
Public-key encryption application that allows secure file
and message exchanges. There is some controversy over the
development and use of this application, in part due to
U.S. national security concerns.
|
| phase |
Location of a position on an
alternating wave form.
|
| phase
shift |
Situation in which the
relative position in time between the clock and data
signals of a transmission becomes unsynchronized. In
systems using long cables at higher transmission speeds,
slight variances in cable construction, temperature, and
other factors can cause a phase shift, resulting in high
error rates.
|
| PHY |
Physical sublayer.
One of two sublayers of the FDDI physical layer. See also
PMD.
|
| physical address |
See
MAC
address.
|
| physical
control layer |
Layer 1 in the
SNA
architectural model. This layer is responsible for
the physical specifications for the physical links between
end systems. Corresponds to the
physical
layer of the OSI model. See also
data
flow control layer,
data
link control layer,
path
control layer,
presentation
services layer,
transaction
services layer, and
transmission
control layer.
|
| physical
layer |
Layer 1 of the
OSI
reference model. The physical layer defines the
electrical, mechanical, procedural and functional
specifications for activating, maintaining, and
deactivating the physical link between end systems.
Corresponds with the
physical
control layer in the SNA model. See also
application
layer,
data
link layer,
network
layer,
presentation
layer,
session
layer, and
transport
layer.
|
| physical layer convergence
procedure |
See
PLCP.
|
| physical media |
See
media.
|
| physical medium |
See
media.
|
| physical medium dependent |
See
PMD.
|
| physical sublayer |
See
PHY.
|
| physical unit |
See
PU.
|
| Physical Unit 2 |
See
PU
2.
|
| Physical Unit 2.1 |
See
PU
2.1.
|
| Physical Unit 4 |
See
PU
4.
|
| Physical Unit 5 |
See
PU
5.
|
| Physics Network |
See
PHYSNET.
|
| PHYSNET |
Physics Network.
Group of many DECnet-based physics research networks,
including HEPnet. See also
HEPnet.
|
piggybacking
|
Process of carrying
acknowledgments within a data packet to save network
bandwidth.
|
| PIM |
Protocol Independent
Multicast. Multicast routing architecture that
allows the addition of IP multicast routing on existing IP
networks. PIM is unicast routing protocol independent and
can be operated in two modes: dense mode and sparse mode.
See also
PIM
dense mode and
PIM
sparse mode.
|
| PIM dense
mode |
One of the two PIM
operational modes. PIM dense mode is data-driven and
resembles typical multicast routing protocols. Packets are
forwarded on all outgoing interfaces until pruning and
truncation occurs. In dense mode, receivers are densely
populated, and it is assumed that the downstream networks
want to receive and will probably use the datagrams that
are forwarded to them. The cost of using dense mode is its
default flooding behavior. Sometimes called dense mode
PIM or PIM DM. Contrast with
PIM
sparse mode. See also
PIM.
|
| PIM DM |
See
PIM
dense mode.
|
| PIM SM |
See
PIM
sparse mode.
|
| PIM
sparse mode |
One of the two PIM
operational modes. PIM sparse mode tries to constrain data
distribution so that a minimal number of routers in the
network receive it. Packets are sent only if they are
explicitly requested at the RP (rendezvous point). In
sparse mode, receivers are widely distributed, and the
assumption is that downstream networks will not
necessarily use the datagrams that are sent to them. The
cost of using sparse mode is its reliance on the periodic
refreshing of explicit join messages and its need for RPs.
Sometimes called sparse mode PIM or PIM SM.
Contrast with
PIM
dense mode. See also
PIM
and
RP
(rendezvous point).
|
| pin location |
A color-coded slot on a
patch panel. Cable wires are punched down using a punch
tool to make an electrical connection that allows the
network to function.
|
| ping |
Command that uses the ICMP
protocol to verify the hardware connection and the logical
address of the network layer. This is a very basic testing
mechanism.
|
| ping-ponging |
Phrase used to describe the
actions of a packet in a two-node routing loop.
|
| pixel |
The smallest element of a
display image, corresponding to a single displayed spot or
color triad on a display, or to a single input spot from a
camera. (A word coined from the phrase "picture
element.")
|
| plain old telephone service |
See
PSTN.
|
| PLC |
Packet line card.
Card on the LightStream 2020 ATM switch that can be
configured only as an edge card. A PLC, in conjunction
with an access card, supports up to eight Ethernet or two
FDDI edge ports.
|
| PLCP |
Physical layer
convergence procedure. Specification that maps
ATM cells into physical media, such as T3 or E3, and
defines certain management information.
|
| plesiochronous
transmission |
Term describing digital
signals that are sourced from different clocks of
comparable accuracy and stability. Compare with
asynchronous
transmission,
isochronous
transmission, and
synchronous
transmission.
|
| PLP |
Packet level
protocol. Network layer protocol in the X.25
protocol stack. Sometimes called X.25 Level 3 or X.25
Protocol. See also
X.25.
|
| PLU |
Primary LU.
The LU that is initiating a session with another LU. See
also
LU.
|
| PMD |
Physical medium
dependent. Sublayer of the FDDI physical layer
that interfaces directly with the physical medium and
performs the most basic bit transmission functions of the
network. See also
PHY.
|
| PNNI |
Private
Network-Network Interface. ATM Forum
specification that describes an ATM virtual circuit
routing protocol, as well as a signaling protocol between
ATM switches. Used to allow ATM switches within a private
network to interconnect. Sometimes called Private
Network Node Interface.
|
| point of presence |
See
POP.
|
| point
-to- point connection |
One of two fundamental connection types. In ATM, a point-to-point connection can be a unidirectional or bidirectional connection between two ATM end-systems. Compare point-to-multipoint connection.
|
| point-
to-multipoint connection |
One of two fundamental connection types. In ATM, a point-to-multipoint connection is a unidirectional connection in which a single source end-system (known as a root node) connects to multiple destination end-systems (known as leaves). Compare point-to-point connection.
|
| Point-to-Point Protocol |
See
PPP.
|
| poison reverse updates |
Routing updates that
explicitly indicate that a network or subnet is
unreachable, rather than implying that a network is
unreachable by not including it in updates. Poison reverse
updates are sent to defeat large routing loops. The Cisco
IGRP implementation uses poison reverse updates.
|
| policy-based routing |
See
policy
routing.
|
| policy
routing |
Routing scheme that forwards
packets to specific interfaces based on user-configured
policies. Such policies might specify that traffic sent
from a particular network should be forwarded out one
interface, while all other traffic should be forwarded out
another interface.
|
| poll/final bit |
See
P/F.
|
| polling |
Access method in which a
primary network device inquires, in an orderly fashion,
whether secondaries have data to transmit. The inquiry
occurs in the form of a message to each secondary that
gives the secondary the right to transmit.
|
| POP |
Point of presence.
Point of presence is the point of interconnection between
the communication facilities provided by the telephone
company and the building's main distribution facility.
|
| port |
1.) Interface on an
internetworking device (such as a router).
2.) In IP terminology, an
upper-layer process that is receiving information from
lower layers.
3.) To rewrite software or
microcode so that it will run on a different hardware
platform or in a different software environment than that
for which it was originally designed. 4. A female plug on
a patch panel which accepts the same size plug as an RJ45
jack. Patch cords are used in these ports to cross connect
computers wired to the patch panel. It is this cross
connection which allows the LAN to function.
4.) A female plug on a patch panel which accepts the same
size plug as an RJ45 jack. Patch cords are used in these
ports to cross connect computers wired to the patch panel.
It is this cross connection which allows the LAN to
function.
|
| POST |
Power-on self test.
Set of hardware diagnostics that runs on a hardware device
when that device is powered up. On a LightStream 2020 ATM
switch, for example, the NP, switch card, and line card
all perform the POST.
|
| Post, Telephone, and
Telegraph |
See
PTT.
|
| POTS |
Plain old telephone
service. See
PSTN.
|
| power-on self test |
See
POST.
|
power-on
servicing
|
Feature on the LightStream
2020 ATM switch that allows faulty components to be
diagnosed, removed, and replaced while the rest of the
switch continues to operate normally. Sometimes
abbreviated POS. Sometimes called hot swapping.
See also
OIR.
|
| power tray |
Power supply for a
LightStream 2020 ATM switch. A LightStream 2020 switch can
have one or two bulk power trays. In a redundant system,
the two power trays load share, but each can power the
entire system in the event that the other fails. The power
tray can provide either AC or DC power to the switch.
|
| PPP |
Point-to-Point
Protocol. A successor to SLIP, PPP provides
router-to-router and host-to-network connections over
synchronous and asynchronous circuits. See also
SLIP.
|
presentation
layer
|
Layer 6 of the
OSI
reference model. This layer ensures that information
sent by the application layer of one system will be
readable by the application layer of another. The
presentation layer is also concerned with the data
structures used by programs and therefore negotiates data
transfer syntax for the application layer. Corresponds
roughly with the
presentation
services layer of the SNA model. See also
application
layer,
data
link layer,
network
layer,
physical
layer,
session
layer, and
transport
layer.
|
presentation
services layer
|
Layer 6 of the
SNA
architectural model. This layer provides network resource
management, session presentation services, and some
application management. Corresponds roughly with the
presentation
layer of the OSI model. See also
data
flow control layer,
data
link control layer,
path
control layer,
physical
control layer,
transaction
services layer, and
transmission
control layer.
|
Pretty Good Privacy
|
See
PGP.
|
| PRI |
Primary Rate
Interface. ISDN interface to primary rate access.
Primary rate access consists of a single 64-Kbps D channel
plus 23 (T1) or 30 (E1) B channels for voice or data.
Compare to
BRI.
See also
BISDN,
ISDN,
and
N-ISDN.
|
| primary |
See
primary
station.
|
| Primary LU |
See
PLU.
|
| Primary Rate Interface |
See
PRI.
|
| primary
ring |
One of the two rings that
make up an FDDI or CDDI ring. The primary ring is the
default path for data transmissions. Compare with
secondary
ring.
|
| primary
station |
In bit-synchronous data link
layer protocols such as HDLC and SDLC, a station that
controls the transmission activity of secondary stations
and performs other management functions such as error
control through polling or other means. Primary stations
send commands to secondary stations and receive responses.
Also called, simply, a primary. See also
secondary
station.
|
| print server |
Networked computer system
that fields, manages, and executes (or sends for
execution) print requests from other network devices.
|
| priority queuing |
Routing feature in which
frames in an interface output queue are prioritized based
on various characteristics such as packet size and
interface type.
|
| private branch exchange |
See
PBX.
|
Private Network-Network
Interface
|
See
PNNI.
|
| Private Network Node
Interface |
See
PNNI. |
| process switching |
Operation that provides full
route evaluation and per-packet load balancing across
parallel WAN links. Involves the transmission of entire
frames to the router CPU where they are repackaged for
delivery to or from a WAN interface, with the router
making a route selection for each packet. Process
switching is the most resource-intensive switching
operation that the CPU can perform.
|
| programmable read-only
memory |
See
PROM.
|
| PROM |
Programmable
read-only memory. ROM that can be programmed
using special equipment. PROMs can be programmed only
once. Compare with
EPROM.
|
| propagation delay |
Time required for data to
travel over a network, from its source to its ultimate
destination.
|
| protocol |
1.) Formal description of a
set of rules and conventions that govern how devices on a
network exchange information. 2.) Field within an IP
datagram that indicates the upper layer (Layer 4) protocol
sending the datagram.
|
| protocol address |
See
network
address.
|
| protocol analyzer |
See
network
analyzer.
|
| protocol control information |
See
PCI.
|
| protocol converter |
Enables equipment with
different data formats to communicate by translating the
data transmission code of one device to the data
transmission code of another device.
|
| protocol data unit |
See
PDU.
|
| Protocol Independent
Multicast |
See
PIM.
|
| protocol
stack |
Set of related
communications protocols that operate together and, as a
group, address communication at some or all of the seven
layers of the OSI reference model. Not every protocol
stack covers each layer of the model, and often a single
protocol in the stack will address a number of layers at
once. TCP/IP is a typical protocol stack.
|
| protocol translator |
Network device or software
that converts one protocol into another, similar,
protocol.
|
| proxy |
Entity that, in the interest
of efficiency, essentially stands in for another entity.
|
| proxy Address Resolution
Protocol |
See
proxy
ARP.
|
| proxy ARP |
Proxy Address
Resolution Protocol. Variation of the ARP
protocol in which an intermediate device (for example, a
router) sends an ARP response on behalf of an end node to
the requesting host. Proxy ARP can lessen bandwidth use on
slow-speed WAN links. See also
ARP.
|
proxy explorer
|
Technique that minimizes
exploding explorer packet traffic propagating through an
SRB network by creating an explorer packet reply cache,
the entries of which are reused when subsequent explorer
packets need to find the same host.
|
| proxy
polling |
Technique that alleviates
the load across an SDLC network by allowing routers to act
as proxies for primary and secondary nodes, thus keeping
polling traffic off of the shared links. Proxy polling has
been replaced by SDLC Transport. See
SDLC
Transport.
|
| PSDN |
Packet-switched data
network. See
PSN
(packet-switched network).
|
| PSE |
Packet switch
exchange. Essentially, a switch. The term PSE is
generally used in reference to a switch in an X.25 PSN.
See also
switch.
|
|
PSN |
1. Packet-switched
network. Network that utilizes packet-switching
technology for data transfer. Sometimes called a packet-switched
data network (PSDN). See
packet
switching.
2. Packet-switching node. Network node
capable of performing packet switching functions. See also
packet
switching.
|
|
PSNP |
Partial sequence number PDU (PSNP)—PSNPs are used to request an LSP
(or LSPs) and acknowledge receipt of an LSP (or LSPs).
|
| PSTN |
Public Switched
Telephone Network. General term referring to the
variety of telephone networks and services in place
worldwide. Sometimes called plain old telephone service
(POTS).
|
| PTT |
Post, Telephone, and
Telegraph. Government agency that provides
telephone services. PTTs exist in most areas outside North
America and provide both local and long-distance telephone
services.
|
| PU |
Physical unit.
SNA component that manages and monitors the resources of a
node, as requested by an SSCP. There is one PU per node.
|
| PU 2 |
Physical Unit 2.
SNA peripheral node that can support only DLUs that
require services from a VTAM host and that are only
capable of performing the secondary LU role in SNA
sessions.
|
| PU 2.1 |
Physical Unit type
2.1. SNA network node used for connecting peer
nodes in a peer-oriented network. PU 2.1 sessions do not
require that one node reside on VTAM. APPN is based upon
PU 2.1 nodes, which can also be connected to a traditional
hierarchical SNA network.
|
| PU 4 |
Physical Unit 4.
Component of an IBM FEP capable of full-duplex data
transfer. Each such SNA device employs a separate data and
control path into the transmit and receive buffers of the
control program.
|
| PU 5 |
Physical Unit 5.
Component of an IBM mainframe or host computer that
manages an SNA network. PU 5 nodes are involved in routing
within the SNA path control layer.
|
| public data network |
See
PDN.
|
| Public Switched Telephone
Network |
See
PSTN.
|
| pull string |
Strong, heavy string used to
pull cable in multiple runs.
|
| pulse amplitude modulation |
See
PAM.
|
| pulse code modulation |
See
PCM.
|
| pulse
density |
See
ones
density.
|
| Punch Tool |
Spring-loaded tool used for
cutting and connecting wire in a jack or on a patch panel.
|
| PUP |
PARC Universal
Protocol. Protocol similar to IP developed at
PARC.
|
| PVC |
Permanent virtual
circuit. Virtual circuit that is permanently
established. PVCs save bandwidth associated with circuit
establishment and tear down in situations where certain
virtual circuits must exist all the time. Called a permanent
virtual connection in ATM terminology. Compare with
SVC.
|
| PVP |
Permanent virtual
path. Virtual path that consists of PVCs. See
also
PVC
and
virtual
path.
|
