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.See PSN (packet-switching node).PAD.packet assembler/disassembler.A device used to connect simple devices (suchas character-mode terminals) that do not support the full functionality of a particularprotocol to a network.PADs buffer data and assemble and disassemble packets sent tosuch end devices.Palo Alto Research Center.See PARC.PAM.pulse amplitude modulation.A modulation scheme in which the modulatingwave is caused to modulate the amplitude of a pulse stream.Compare with AM andFM.See also modulation.PAP.Password Authentication Protocol.An authentication protocol that allows PPPpeers to authenticate one another.The remote router attempting to connect to the localrouter is required to send an authentication request.Unlike CHAP, PAP passes thepassword and host name or username in the clear (unencrypted).PAP does not itselfprevent unauthorized access, but merely identifies the remote end.The router or accessserver then determines whether that user is allowed access.PAP is supported only onPPP lines.Compare with CHAP.parallel channel.A channel that uses bus and tag cables as a transmission medium.Compare with ESCON channel.See also bus and tag channel. CH01.book Page 461 Friday, January 7, 2000 5:35 PMpath name 461parallelism.Multiple paths existing between two points in a network.These pathsmay be of equal or unequal cost.Parallelism is often a network design goal; if one pathfails, there is redundancy in the network to ensure that an alternate path to the samepoint exists.parallel transmission.A method of data transmission in which the bits of a datacharacter are transmitted simultaneously over a number of channels.Compare withserial transmission.PARC.Palo Alto Research Center.A research and development center operated byXEROX.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.A process for checking the integrity of a character.A parity checkinvolves appending a bit that makes the total number of binary 1 digits in a characteror word (excluding the parity bit) either odd (for odd parity) or even (for even parity).partial mesh.A network in which devices are organized in a mesh topology, withsome network nodes organized in a full mesh, but with others that are connected toonly one or two other nodes in the network.A partial mesh does not provide the levelof redundancy of a full mesh topology, but is less expensive to implement.Partial meshtopologies are generally used in the peripheral networks that connect to a fully meshedbackbone.See also full mesh and mesh.Password Authentication Protocol.See PAP.path control layer.Layer 3 in the SNA architectural model.This layer performssequencing services related to proper data reassembly.The path control layer is alsoresponsible 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.An SNA concept that consists of lower-level components thatcontrol the routing and data flow through an SNA network and handle physical datatransmission between SNA nodes.Compare with NAU.path cost.See cost.path name.The full name of a UNIX, DOS, or LynxOS file or directory, includingall directory and subdirectory names.Consecutive names in a path name are typicallyseparated by a forward slash (/) or a backslash (\), as in /usr/app/base/config. CH01.book Page 462 Friday, January 7, 2000 5:35 PM462 payloadpayload.The portion of a frame that contains upper-layer information (data).PBX.private branch exchange.A digital or analog telephone switchboard located onthe subscriber premises and used to connect private and public telephone networks.PCI.protocol control information.Control information added to user data to comprisean OSI packet.The OSI equivalent of the term header.See also header.PCM.pulse code modulation.The transmission of analog information in digital formthrough sampling and encoding the samples with a fixed number of bits.PCR.peak cell rate.A parameter defined by the ATM Forum for ATM trafficmanagement.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.A network operated either by a government (as in Europe)or by a private concern to provide computer communications to the public, usually fora fee.PDNs enable small organizations to create a WAN without all the equipmentcosts of long-distance circuits.PDU.protocol data unit.An OSI term for packet.See also BPDU and packet.peak cell rate.See PCR.peak rate.The maximum rate, in kilobits per second, at which a virtual circuit cantransmit.peer-to-peer computing.Each network device runs both client and server portionsof an application.Also, communication between implementations of the same OSIreference model layer in two different network devices.Compare with client/servercomputing.performance management.One of five categories of network management definedby ISO for management of OSI networks.Performance management subsystems areresponsible for analyzing and controlling network performance including networkthroughput and error rates.See also accounting management, configurationmanagement, fault management, and security management.peripheral node.In SNA, a node that uses local addresses and is therefore notaffected by changes to network addresses.Peripheral nodes require boundary functionassistance from an adjacent subarea node.permanent virtual circuit.See PVC. CH01.book Page 463 Friday, January 7, 2000 5:35 PMphysical medium 463permanent virtual connection.See PVC.permanent virtual path.See PVP.permit processing.See traffic policing.P/F.poll/final bit [ Pobierz całość w formacie PDF ] |
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