P/F: Poll/Final bit
Poll/Final bit (P/F) refers to the 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.

p2mp: Point-to-multipoint
Point-to-multipoint (P2MP), a Cisco-defined technology, refers to the communication between a series of receivers and transmitters to a central location. P2MP typically is set up in three segments to enable frequency re-use.

P2P: Peer-to-peer
Peer-to-peer (P2P) is a network architecture that allows hardware or software to function on a network without the need for central servers. Peer-to-peer approach has also been popularized by some Net software applications such as Groove and Napster.

Packet
A packet, in data networking, is one unit of binary data formatted for transmission on a network. To improve communication performance and reliability, each message sent between two network devices is often subdivided into packets by the underlying hardware and software. Packet formats generally include a header, the body containing the message data (also known as the payload), and sometimes a footer (also known as the trailer). The packet header lists the origin and destination of the packet and often indicates the length of the message data. The packet footer contains data that signifies the end of the packet. Both the packet header and footer may contain error-checking information.

Packet Analysis
Packet analysis is a process for a software program or a hardware device (plus software) to capture packets and then decode their headers and trailers information to understand the data and information inside the packet encapsulated by the protocol.

Packet Analyzer
Packet Analyzer is a software or hardware tool to capture and analysis packets. It is also called protocol analyzer since the tool must decode the protocols that encapsulate the packets.

Packet driver
Packet driver is a type of Local area network (LAN) software that divides data into packets for sending on the network, and reassembles the data into its original form when it arrives at its destination.

Packet Pain
Packet pain is technique proposed to assess the available bandwidth of a network. The most spread way to do this nowadays is through the use of the algorithm slow-start, which consists of sending a certain number of packets and seeing how many of them are acknowledged by the receiver.

Packet Sniffer
Packet sniffers, also known as Network Analyzers or Packet Analyzer or Protocol Analyzer, are software programs which can capture traffic passing over a network or part of a network. As data streams travel back and forth over the network, the program captures each packet and eventually decodes and analyzes its content according to the protocol structure.

Packet Switch
Packet Switch routes packets from origin to destination along the most efficient path individually and allows a communications channel to be shared by multiple connections. Packet switching is used to optimize the use of the bandwidth available in a network, to minimize the transmission latency (i.e. the time it takes for data to pass across the network), and to increase robustness of communication.

Packet Switch Network
Packet Switch Network refers to the type of network in which relatively small units of data called packets are routed through a network based on the destination address contained within each packet. Breaking communication down into packets allows the same data path to be shared among many users in the network. This type of communication between sender and receiver is known as connectionless (rather than dedicated). Most traffic over the Internet uses packet switching and the Internet is basically a connectionless network.

Packet Switching
Packet switching is the process in which packets (units of information carriage) are individually routed between nodes over data links which might be shared by many other nodes. This contrasts with the circuit switching, which sets up a dedicated connection between the two nodes for their exclusive use for the duration of the communication. Packet switching is used to optimize the use of the bandwidth available in a network, to minimize the transmission latency (i.e. the time it takes for data to pass across the network), and to increase robustness of communication. In packet-switched networks (e.g., Internet), the data is split up into packets, each labeled with the complete destination address and routed individually. Circuit switched networks, such as the Public Switched Telephone Network (PSTN), also perform routing to find paths for circuits over which large amounts of data can be sent without continually repeating the complete destination address.

Packet-level Inverse Multiplexing
Packet-level Inverse Multiplexing is a method of inverse multiplexing in which the inverse mux performs its function at the packet level using the MP or MPP protocol. One data packet goes over the first circuit, the next goes over the second circuit, and so on, until all the data packets are distributed over all the available circuits. The receiving end adjusts for network-induced delay and reassembles the data packets into their proper order. This inverse multiplexing technique is also referred to as load balancing. Telecommuting applications use packet-level inverse multiplexing.

Packet-switching Node
Packet-switching Node is a node in a packet-switching network that contains data switches and equipment for controlling, formatting, transmitting, routing, and receiving data packets.

PAD: Packet Assembler/Disassembler
Packet Assembler/Disassembler (PAD) is the component of a packet transmission system that segments the transmit data into packets and returns the received data to longer messages.

PAM: Port to Application Mapping
Port to Application Mapping (PAM) is a technique that allows user to customize TCP or UDP port numbers for network services or applications.

PAN: Personal Area Network
A personal area network (PAN) is a computer network used for communications among computer devices (including telephones and personal digital assistants) close to one person. The devices may or may not belong to the person in question. The reach of a PAN is typically a few meters. PANs can be used for communication among the personal devices themselves (intrapersonal communication), or for connecting to a higher level network and the Internet (an uplink). Personal area networks may be wired with computer buses such as USB and FireWire. A wireless personal area network (WPAN) can also be made possible with network technologies such as IrDA and Bluetooth.

Parallel Channel
Parallel Channel refers to the channel that uses bus and tag cables as a transmission medium.

Parallel Transmission
Parallel Transmission is a method of data transmission in which the bits of a data character are transmitted simultaneously over a number of channels/ports. In parallel transmission, coded information are transmitted via a system with multiple ports/channels. The port 1 is used to transport the first MSB (Most Significant Bit) and the second port carries the second MSBs, so on and so forth.

Parallelism
Parallelism in networking 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.

PARC: Palo Alto Research Center
Palo Alto Research Center (PARC) is a 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.

Parent Peer Group
Parent Peer Group, a concept in ATM network, is a peer group that acts as a "parent" to a subordinate peer group. Organizing peer groups hierarchically reduces the exchange of PTSPs.

Parity
Parity refers to the quality of being either odd or even for a number. Parity is commonly used in data communications to ensure the validity of data. Each device must determine whether it will use even parity, odd parity, or no parity. The sending device adds the 1s in each string it sends and determines whether the sum is even or odd. Then, it adds an extra bit, called a parity bit, to the string. If even parity is in use, the parity bit makes the sum of the bits even; if odd parity is in use, the parity bit makes the sum of the bits odd.

Parity Check
Parity Check is the 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).

Parking a Domain Name
Parking a Domain Name is the process by which someone selects a domain name, and "parks" it by registering the domain name under someone's name servers. Parking can be done by anyone, to anyone else who has active name servers. However, parking a domain name alone will result in no service (webhosting, e-mail) for that particular domain name.

Partial Mesh
Partial Mesh is a type of network topology in which some nodes are organized in a full mesh scheme but others are only connected to one or two in the network. Partial mesh topology is commonly found in peripheral networks connected to a full meshed backbone. It is less expensive to implement and yields less redundancy than full mesh topology.

Passive FTP
Passive FTP is actually the normal mode of the FTP service, which is a more secure form of data transfer in which the flow of data is set up and initiated by the File Transfer Program (FTP) client rather than by the FTP server program. The other FTP mode is called the active FTP, in which the client connects from a random unprivileged port (N > 1023) to the FTP server's command port, port 21. Then, the client starts listening to port N+1 and sends the FTP command PORT N+1 to the FTP server. The server will then connect back to the client's specified data port from its local data port, which is port 20.

PASV: Passive mode FTP
Passive mode FTP (PASV) is an alternative mode for establishing File Transfer Protocol (FTP) connections. PASV mode is designed for FTP clients behind firewalls, because many client firewalls reject incoming messages like these FTP requests. In passive mode FTP the client initiates both connections to the server, solving the problem of firewalls filtering the incoming data port connection to the client from the server.

Patch Cable
Patch Cable is a twisted-pair or fiber optic jumper cable used to connect an NIC and a media segment, etc.

Path Control Layer
Path Control Layer is the layer 3 in the SNA architectural model, corresponding roughly with the network layer of the OSI model. This layer performs sequencing services related to proper data reassembly. The path control layer also is responsible for routing.

Path Control Network
Path Control Network is an 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.

Path Name
Path Name is the full name of a DOS, Mac OS, or UNIX file or directory, including all directory and subdirectory names. Consecutive names in a path name typically are separated by a backslash (\) for DOS, a colon (:) for Mac OS, and a forward slash (/) for UNIX.

Path State Block
The path state block is the information store for per LSP path information by RSVP. The sender template {IP Address of ingress : LSP-ID} combines with the session object {IP address of tunnel end-point : tunnel-id : extended-tunnel-id} to uniquely identify the LSP tunnel.

Paul Baran
Paul Baran (born in 1926) was one of the developers of packet-switched networks along with Donald Davies and Leonard Kleinrock. He was born in Poland, but his family moved to Boston in 1928. He obtained his Masters degree in Engineering from UCLA in 1959 and began working for the RAND Corporation in the same year.

Payload
Payload is the portion of a cell, frame, or packet that contains upper-layer information (data). The whole frame/packet or cell becomes the payload of the lower level communications.

PBR: Policy-based Routing
Policy-based routing (PBR), also known as policy routing, refers to a technique used to make routing decisions based on policies pre-set by the network administrator.

PC Card
PC Card, also known as PCMCIA card is the card developed by the Personal Computer Memory Card International Association (PCMCIA). It is about the size of a credit card, it's often the card in a laptop that you plug a network connection into.

PCI: Protocol Control Information
Protocol Control Information (PCI) is the control information added to user data to comprise an OSI packet. The OSI equivalent of the term header.

PC-Network
PC-Network was a broadband LAN product consisting of network cards, cables, and a small device driver known as NetBIOS (Network Basic Input/Output System). The PC-Network has been replaced by the Ethernet technologies which is dominant the LAN. Much software was written for use with the NetBIOS Application Programmer's Interface (API), so, even though the PC Network hardware is no longer in use and the NetBIOS device driver is no longer needed, the NetBIOS API has remained as a living artifact.

PCR: Peak Cell Rate
Peak Cell Rate (PCR) is an ATM service 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.

PCS: Personal Communications Service
Personal Communications Service(PCS) is an advanced network architecture that provides personal, terminal, and service mobility. In the United States, PCS spectrum has been allocated for broadband, narrowband, and unlicensed services.

PDN: Public/private/packet Data Network
Public/private/packet Data Network (PDN) refers to a public or private packet-based network for data communication, such as an IP or X.25 based network.

PDU: Protocol Data Unit
Protocol Data Unit (PDU) is the OSI term for packet, which is the data unit formated to be transferred over the network layer. PDU consists of this layer's Header, Trailer and Data encapsulated.

PE Router
The provider edge (PE) router is a router between one network service provider's area and areas administered by other network providers or Internet Service Providers (ISPs).

Peak Rate
Peak Rate means the maximum rate, in kilobits per second (kbps) or megabits per second (mbps) or gigabits per second (gbps), at which a virtual circuit or circuit can transmit.

Peer Group
Peer Group is a collection of ATM nodes that share identical topological databases and exchange full link state information with each other. Peer groups are arranged hierarchically to prevent excessive PTSP traffic.

PeerGuardian
PeerGuardian is a simple software firewall designed for use with Microsoft Windows P2P file sharing clients. PeerGuardian works by maintaining a database of IP addresses, logging and/or blocking incoming requests coming from those addresses.

Peer-to-Peer Computing
Peer-to-Peer Computing (P2P Computing) is a type of distributed computing using P2P technologies that employ distributed resources to perform a function in a decentralized manner. Some of the benefits of a P2P computing include: improving scalability by avoiding dependency on centralized points; eliminating the need for costly infrastructure by enabling direct communications among clients; and enabling resource aggregation.

Performance Management
Performance Management is one of five components of network management. The purpose of Performance Management is to measure and make available various aspects of network performance for network performance monitoring and optimization. The network performance variables include network throughput, user response times, and line utilization.

Performance Monitoring
Performance Monitoring is a network management feature that provides a variety of automatic functions to aid in the maintenance and operation of the network. Performance monitoring is continuous, in-service monitoring of transmission quality that uses software-provisionable performance parameters.

Peripheral Node
Peripheral Node is a term used in SNA-based network, that uses local addresses and therefore is not affected by changes to network addresses. Peripheral nodes require boundary function assistances from an adjacent subarea node.

Permanent Virtual Circuit Interface Priority Queueing
Permanent Virtual Circuit Interface Priority Queueing is an interface-level priority queueing scheme in a frame relay network, in which prioritization is based on destination PVC rather than packet contents.

PGL: Peer Group Leader
Peer Group Leader(PGL), a concept in ATM network, refers to a node in a peer group that performs the functions of the LGN. Peer group leaders exchange PTSPs with peer nodes in the parent peer group to inform those nodes of the peer group's attributes and reachability and to propagate information about the parent group and the parent group's parents to the nodes in the peer group.

Phase Shift
Phase Shift refers to the 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, result in high error rates.

PHB: Per-Hop Behaviour
Per-Hop Behaviour (PHB) is a term used in Diff-Serv (Differentiated Services) or MPLS. It defines the policy/priority applied to a packet when traversing a hop (such as a router) in a Diff-Serv network.

PHP: Penultimate Hop Popping
Penultimate Hop Popping (PHP) is a function performed by certain routers in an MPLS-enabled network. It refers to the process whereby the outermost label of an MPLS-tagged packet is removed by a Label Switched Router (LSR) before the packet is passed to an adjacent Label Edge Router (LER). PHP is important in a Layer 3 MPLS VPN (RFC2547) environment as it reduces the load on the LER.

PHY: Physical Layer Device
Physical Layer Device (PHY) is the term used for a transceiver in Fast Ethernet and Gigabit Ethernet systems.

Physical Control Layer
Physical Control Layer is the layer 1 in the SNA architectural model. It is equivalent to the physical layer in the OSI 7 layers model. This layer is responsible for the physical specifications of the physical links between end systems.

Physical Layer
Physical Layer is the first layer in the OSI seven layers reference model, which defines the electrical and optical properties of signal transmission.

PHYSNET: Physics Network
Physics Network(PHYSNET) is a group of many DECnet-based physics research networks, including HEPnet. It is no longer in use.

PIAFS: Personal Handyphone Internet Access Forum Standard
Personal Handyphone Internet Access Forum Standard (PIAFS), also known as PHS Internet Access Forum Standard, is an ITU-T standard for support by ISDN of data terminal equipment with V-series type interfaces.

Piggybacking
Piggybacking in networking refers to the process of carrying acknowledgments within a data packet to save network bandwidth.

Ping: Packet internet groper
Packet internet groper (Ping) is a popular TCP/IP network utility using the Internet Control Message Protocol (ICMP) to determine the availability and responsiveness of network hosts. A system administrator uses the Ping tool to see if a computer is operating as well as if network connections are intact. The Internet Control Message Protocol (ICMP) Echo function used by the Ping tools is detailed in RFC 792. A small packet is sent through the network to a particular IP address.

Ping-Ponging
Ping-Ponging in networking refers to the situation when a packet is looping between two nodes.

PLCP: Physical Layer Convergence Procedure
Physical Layer Convergence Procedure(PLCP) is the specification that maps ATM cells into physical media, such as T3 or E3, and defines certain management information.

PLU: Primary Logical Unit
Primary Logical Unit (PLU), a concept in SNA network, is the LU that is initiating a session with another logic unit (LU).

PMD: Physical Medium Dependent
Physical Medium Dependent(PMD) is a sublayer of the FDDI physical layer that interfaces directly with the physical medium and performs the most basic bit transmission functions of the network.

PMD: Polarization Mode Dispersion
Polarization Mode Dispersion (PMD) is an inherent property of all optical media, caused by the difference in the propagation velocities of light in the orthogonal principal polarization states of the transmission medium.

POD: Packet of Disconnect
Packet of Disconnect (POD) is the process that allows a PPP session to be verified and then terminated by the network access server. It terminates connections on the network access server when particular session attributes are identified. The POD client, residing on a UNIX workstation, sends disconnect packets to the POD server running on the network access server using session information obtained from AAA. The network access server terminates any inbound user session with one or more matching key attributes. It rejects requests that do not have the required fields or where an exact match is not found.

PoE: Power over Ethernet
Power over Ethernet (PoE) technology describes any system to transmit electrical power, along with data, to remote devices over standard twisted-pair cables in an Ethernet network. This technology is useful for powering IP telephones, wireless LAN access points, webcams, Ethernet hubs, computers, and other appliances where it would be inconvenient or infeasible to supply power separately. The technology is somewhat comparable to POTS telephones, which also receive power and data (although analog) through the same cable. It works with an unmodified Ethernet cabling infrastructure.

Point-to-Multipoint Connection
Point-to-Multipoint Connection is one of two fundamental connection types in ATM networking. 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).

Point-to-point Connection
Point-to-point Connection is one of two fundamental connection types in ATM networking. In ATM, a point-to-point connection can be a unidirectional or bidirectional connection between two ATM end-systems.

Poison Reverse
Poison Reverse is a routing update that explicitly indicates 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.

POL-34
POL-34 is a Polish academic computer network created to provide high-speed Internet access and to conduct network-based research. Most of the government-founded higher education organisations and all of metropolitan area networks in Poland are connected to POL-34.

Policy
Policy in networking refers to any defined rule that determines the use of resources within the network. A policy can be based on a user, a device, a subnetwork, a network, or an application.

Policy Decision Point
Policy Decision Point is a system, usually a server that makes decisions based on pre-defined networking policies. It has global knowledge of network policies, and is consulted by network devices (like routers) that enforce the policies.

Policy Enforcement Point
Policy Enforcement Point is a network device on which policy decisions are carried out or enforced. Usually it is a network node like a router or a switch.

Policy Routing
Policy Routing, also known as Policy Based Routing, is a routing scheme that forwards packets to specific interfaces based on pre-configured policies by netowrk admins. Such policies might specify that traffic sent from a particular network should be forwarded out one interface, and all other traffic should be forwarded out another interface.

Policy Server
Policy Server, also known as policy decision point, is the server that holds policies for reference by and decision over client routers and switches.

Polling
Polling is an 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. In telecommunications, polling is a long distance carrier access method in which a non-local call is carried by the long distance carrier via a dedicated trunk facility for either the first or last part of the call's journey, and on the carrier's network for the middle part of the journey.

Port
Port means a few things in networking: (1) A hardware connection point for a cable at a network device. Hubs and switches typically provide multiple ports for connecting Ethernet devices. These hardware ports have different physical shapes such as male, female, round, rectangular, square, oblong, etc. (2) A network port is an identification of an application in the TCP- or UDP-transported datagram.

Port Address Translation
Port Address Translation, also known as Network Port Address Translation (NPAT), is a feature of a Network Address Translation (NAT) device that translates not only IP addresses but also TCP or UDP ports between a host and port on an outside network to a host and port on an inside network. NPAT allows one single IP address to be used for many internal hosts. With NPAT one outside IP address can account for over 64000 inside hosts.

Port Mirroring
Port mirroring, also known as port spanning or port monitoring function, is a function in many managed switches that is used on a network switch to send a copy of all network packets seen on one switch port to a monitoring network connection on another switch port. This is commonly used for network appliances that require monitoring of network traffic, such as an intrusion-detection system. A network administrator uses port mirroring as a diagnostic tool or debugging feature, especially when fending off an attack.

Port Number
Port numbers are associated with TCP and UDP protocols designed to distinguish multiple applications running on a single device with one IP address from one another. Since many network applications may be running on the same machine, computers need something to make sure the correct software application on the destination computer gets the data packets from the source machine, and to make sure replies get routed to the correct application on the source computer. This is accomplished through the use of the TCP or UDP "port numbers". In the TCP and UDP header, there are "SourcePort" and "DestinationPort" fields which are used to indicate the message sending process and receiving process identities defined. The combination of the IP address and the port number is called "socket".

Port Triggering
Port triggering is a function offered by some NAT-enabled routers, to enable access to a computer within the network from the outside, on a specific port number. It is activated by data being sent out of the network on that specific port.

Portal
A portal is a kind of public Web sites which have a lot of diverce information and services such as email, news, stock quotes, etc. Yahoo.com is a Portal. Portal is also used in some corporations intranet sites, known as enterprise information or corporate portals, which serves as the central point of informaion and service navigation.

POSI: Promoting Conference for OSI
Promoting Conference for OSI (POSI) is a group of executives from the six major Japanese computer manufacturers and Nippon Telephone and Telegraph that sets policies and commits resources to promote OSI.

POTS Splitter
POTS Splitter is a device or a part of a device that enables both a DSL data device and a standard analog device (such as a telephone) to share the same POTS line connected to the ADSL switches.

Power-on Servicing
Power-on Servicing, also known as hot swapping, is a feature in many devices that allows faulty components to be diagnosed, removed, and replaced while the rest of the device continues to operate normally.

PPS: Packet per second
Packet per second(PPS) is a measure of network bandwidth usage.

PQ/CBWFQ: Priority Queueing/Class-based Weighted Fair Queueing
Priority Queueing/Class-based Weighted Fair Queueing (PQ/CBWFQ) is a queueing scheme that adds strict priority queueing to CBWFQ. Strict priority queueing allows delay-sensitive data, such as voice, to be dequeued and sent first (before packets in other queues are dequeued), giving delay-sensitive data preferential treatment over other traffic.

Preamble
A preamble is a signal used in network communications to synchronize the transmission timing between two or more systems. Proper timing ensures that all systems are interpreting the start of the information transfer correctly. A preamble defines a specific series of transmission pulses that is understood by communicating systems to mean "someone is about to transmit data".

Precloning
Precloning refers to cloning a specified number of virtual access interfaces from a virtual template at system startup or when the command is configured.

Presence technology
Presence technology is a type of application that makes it possible to locate and identify a computing device (including, for example, handheld computers as well as desktop models) wherever it might be, as soon as the user connects to the network. One application of presence technology, instant messaging (IM), is already very popular. Presence technology is expected to be an integral part of third generation (3G) wireless networks, and is likely to be employed across a wide variety of communication devices, including cellphones, PDAs (personal digital assistants), television sets, and pagers.

Presentation Layer
Presentation Layer is the layer 6 in the OSI 7 layers reference model. The primary functions of this layer are: Masks the differences of data formats between dissimilar systems; Specifies architecture-independent data transfer format; Encodes and decodes data; Encrypts and decrypts data; Compresses and decompresses data.

Presentation Services Layer
Presentation Services Layer is the layer 6 of the SNA architectural model, similar to the presentation layer in the OSI model. This layer provides network resource management, session presentation services, and some application management.

PRI: Primary Rate Interface
Primary Rate Interface (PRI) is an ISDN interface for primary rate access, which consists of a single 64-kbps D channel plus 23 (T1) or 30 (E1) B channels for voice or data. PRI intended for larger users, such as business users. The other ISDN interface is the Basic Rate Interface (BRI), which is for homes and small businesses.

Primary Ring
Primary Ring is one of the two rings that make up an FDDI or CDDI ring architecture. The primary ring is the default path for data transmissions.

Primary Station
Primary Station is a concept in bit-synchronous data link layer protocols, such as HDLC and SDLC, 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.

Print Server
A print server is a networked computer or device to which one or more printers are connected and which accepts print jobs from other computers in the network. The print server then sends the data to the appropriate printer that it manages.

Priority Output Queuing
Priority output queuing, also known as priority queuing, is a routing queuing method at a given output interface which allows four priorities of traffic---high, normal, medium, and low. As traffic comes into the router, it is assigned to one of the four output queues based on various characteristics, such as packet size and interface type. Packets on the highest-priority queue are transmitted first. When that queue empties, traffic on the next highest-priority queue is transmitted, and so on. This mechanism assures that during congestion, the highest-priority data does not get delayed by lower-priority traffic. However, if the traffic sent to a given interface exceeds the bandwidth of that interface, lower-priority traffic can experience significant delays.

Private IP address
Private IP addresses, also often called RFC1918 addresses, are the IP addresses set aside by IANA according to IETF RFC 1918 for private use by companies and organizations in their private network. Private IP Addresses cannot be used to connect directly to the Internet because they are non-routable. On the other hand, the public IP addresses are typically owned, either by very large corporations or by ISPs for public to use for routing across any public network such as the Internet. When a user contracts for service from an ISP, the user is allocated to some number of legitimate IP Addresses out of that ISPs pool of public IP addresses. IANA has set aside three address ranges for use by private or non-Internet connected networks. This is referred to as Private Address Space with the reserved address blocks as: 10.0.0.0 to 10.255.255.255 (10/8 prefix) 172.16.0.0 to 172.31.255.255 (172.16/12 prefix) 192.168.0.0 to 192.168.255.255 (192.168/16 prefix).

Private Ports
Private Ports, also known as dynamic ports, refer to one of the classes of the TCP/UDP ports, defined by IETF IANA. The other two classes are the Registered Ports and the Well Known Ports. The Private/Dynamic are those with a port number from 49152 through 65535, which could be used by any company for their private applications, without IANA administration.

Priority Queue
Priority Queue is a routing feature in which frames in an output queue are prioritized based on various characteristics, such as packet size and interface type.

Privileged Process
Privileged Process is the computer process that is authorized (and, therefore, trusted) to perform some security-relevant functions that ordinary processes are not.

PRMD: Private Management Domain
Private Management Domain (PRMD) is the X.400 Message Handling System (MHS) private organization mail system (for example, NASAmail).

Process switching
Process switching is an operation that provides full route evaluation and per-packet load balancing across parallel WAN links. Process switching 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.

Promiscuous Mode
Promiscuous Mode refers to a machine or software reading all packets off the network, regardless of who they are addressed to. This is used by network administrators to diagnose network problems, but also by un-authoized people who are trying to eavesdrop on network traffic (which might contain passwords and other sensitive information). A non-routing node in promiscuous mode can generally only monitor traffic to and from other nodes within the same collision domain (for Ethernet and Wireless LAN) or ring (for Token Ring or FDDI), which is why network switches are used to combat malicious use of promiscuous mode.

Propagation Delay
Propagation Delay is the time required for data to travel over a network from its source to its ultimate destination.

Proprietary
Proprietary refers to information (or other property) that is owned by an individual or an organization and for which the use is restricted by that entity.

Protected Checksum
Protected Checksum is a type of checksum computed for a data object by a means that protects against active attacks that would attempt to change the checksum to make it match changes made to the data object.

Protection Ring
Protection Ring is one of a hierarchy of privileged operation modes of a system that gives certain access rights to processes authorized to operate in that mode.

Protocol
Protocol, also known as network protocol, is a formal set of rules, conventions and data structure that governs how computers exchange information over a network. In other words, network protocol is a standard procedure and format that two data communication devices must understand, accept and use to be able to talk to each other.

Protocol analysis
Protocol analysis is a process for a program or a device to decode network protocol headers and trailers to understand the data and information inside the packet encapsulated by the protocol. To conduct protocol analysis, packets must be captured at real time for line speed analysis or later analysis. Such program or device is called a Protocol Analyzer.

Protocol Analyzer
Protocol Analyzer is a software or a device to decode network protocol headers and trailers to understand the data and information inside the packet encapsulated by the protocol. To conduct protocol analysis, packets must be captured at real time for line speed analysis or later analysis.

Protocol Converter
Protocol Converter is a network equipment that enables different data formats to communicate by translating the data format (protocol) of one device to the data format of another device.

Protocol decoder
Protocol decoder, also known as protocol analyzer, is a software or a device to decode network protocol headers and trailers to understand the data and information inside the packet encapsulated by the protocol. To conduct protocol analysis, packets must be captured at real time for line speed analysis or later analysis.

Protocol decoding
Protocol decoding, also known as protocol analysis, is a process for a program or a device to decode network protocol headers and trailers to understand the data and information inside the packet encapsulated by the protocol. To conduct protocol analysis, packets must be captured at real time for line speed analysis or later analysis. Such program or device is called a Protocol Analyzer or protocol decoder.

Protocol Stack
Protocol Stack, also known as protocol suite or protocol family, refers to a set of related communications protocols that operate together and, as a group, address communications at some or all of the 7 layers of the OSI reference model. TCP/IP is the mostly used protocol stack.

Protocol Suite
Protocol Suite, also known as protocol stack, is a complementary collection of communication protocols used in a computer network. TCP/IP is a typical protocol suite.

Protocol Translator
Protocol Translator, also known as protocol converter, is a network device or software that converts one protocol into another similar protocol.

Protocol Type
Protocol Type is a field in the IP header that identifies the type of header that follows the IP header, typically a Layer 4 header, such as TCP or UDP. ACLs can examine the protocol type to match packets with a particular value in this header field.

Provider Edge Router
Provider Edge Router is the router that locates at a service provider's network and is connected to a customer edge (CE) router directly.

Provisioning
Provisioning refers to the creation of an active subscriber account, or modification of parameters for an existing subscriber account. Provisioning of a subscriber account includes subscriber account registration and device activation.

Proxy ARP
Proxy ARP is a technique for using the ARP protocol to provide an ad hoc routing mechanism. Proxy ARP allows a host, usually a router, to answer ARP requests intended for another machine. By "faking" its identity, the router accepts responsibility for routing packets to the "real" destination. Proxy ARP can help machines on a subnet reach remote subnets without configuring routing or a default gateway.

Proxy Explorer
Proxy Explorer is the technique that minimizes exploding explorer packet traffic propagating through an SRB network by creating an explorer packet reply cache.

Proxy Mode
Proxy Mode refers to a situation where a remote host can be assigned an IP address on the local network through its Connection profile. Local hosts on the network see the remote host as if it were on the local network. When accesses are made to the remote host, the local host acts on behalf of the remote host and replies to requests and forwards packets. Proxy mode can be enabled via the Protocols section of the configuration software.

Proxy polling
Proxy polling is a 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.

Proxy Service
Proxy service is a computer network service that allows clients to make indirect network connections to other network services. A client connects to the proxy server, then requests a connection, file, or other resource available on a different server. The proxy provides the resource either by connecting to the specified server or by serving it from a cache. In some cases, the proxy may alter the client's request or the server's response for various purposes.

PRTG: Paessler Router Traffic Grapher
Paessler Router Traffic Grapher(PRTG) is a network and bandwidth usage monitoring software that has become the Microsoft Windows standard alternative to Multi Router Traffic Grapher (MRTG) for bandwidth and network monitoring.

PSDN: Packet-switched Data Network
Packet-switched Data Network (PSDN), also known as Packet Switched Network (PSN), refers to the network using packet-swtching technologies to transport data packets.

Pseudowire
Pseudowire is a point-to-point connection between pairs of edge routers. Its primary function is to emulate services like Ethernet over an underlying core MPLS (Multiprotocol Label Switching) network through encapsulation into a common MPLS format.

PSS: Packet Switch Stream
Packet Switch Stream (PSS) refers to an X.25-based packet-switched network in UK, provided by British Telecom. Companies and individual users could connect in to the PSS network, via a PSS modem, or an X.25 PAD (Packet Assembler/Disassembler), and a dedicated (four-wire telephone circuit) PSS line, and use it to connect to a variety of online databases and mainframe systems. The PSS modem is connected directly into a computer system; whereas the X.25 PAD was a stand-alone device which allowed up to eight serial RS-232 Data Terminal Equipment terminals to link into PSS. The PSS was closed in June, 2006.

PTI: Payload Type Identifier
Payload Type Identifier is 3-bit descriptor in the ATM cell header indicating the type of payload that the cell contains. Payload types include user and management cells; one combination indicates that the cell is the last cell of an AAL5 frame.

PTSE: PNNI Topology State Element
PNNI Topology State Element(PTSE) refers to a collection of PNNI information that is flooded among all logical nodes within a peer group.

PTSP: PNNI Topology State Packet
PNNI Topology State Packet(PTSP) is a type of PNNI routing packet used to exchange reachability and resource information among ATM switches to ensure that a connection request is routed to the destination along a path that has a high probability of meeting the requested QoS. Typically, PTSPs include bidirectional information about the transit behavior of particular nodes (based on entry and exit ports) and current internal state.

PU 2.1: Physical Unit type 2.1
Physical Unit type 2.1 (PU 2.1) is an 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 also can be connected to a traditional hierarchical SNA network.

PU 2: Physical Unit 2
Physical Unit 2 (PU 2) is an SNA peripheral node that can support only DLUs that require services from a VTAM host and that are capable only of performing the secondary LU role in SNA sessions.

PU 4 : Physical Unit 4
Physical Unit 4 (PU 4) is a component of an IBM Front End Processor (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
Physical Unit 5 (PU 5) is a 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.

PU: Physical Unit
Physical Unit(PU) is an SNA component that manages and monitors the resources of a node, as requested by an SSCP. There is one PU per node.

PVC: Permanent Virtual Circuit
Permanent Virtual Circuit PVC) is a predefined virtual circuit in an ATM or Frame Relay network. A PVC can be equated to a leased line in concept.

PVP Tunneling: Permanent Virtual Path Tunneling
Permanent Virtual Path Tunneling (PVP Tunneling) is a method of linking two private ATM networks across a public network using a virtual path. The public network transparently trunks the entire collection of virtual channels in the virtual path between the two private networks.

PVP: Permanent Virtual Path
Permanent Virtual Path (PVP) is pre-set virtual path that consists of Permanent Virtual Circuits (PVCs) in an ATM and Frame Relay network.

PVST: Per-VLAN Spanning Tree
Per-VLAN Spanning Tree (PVST) maintains a spanning tree instance for each VLAN configured in the network. It uses ISL Trunking and allows a VLAN trunk to be forwarding for some VLANs while blocking for other VLANs. Since PVST treats each VLAN as a separate network, it has the ability to load balance traffic (at layer-2) by forwarding some VLANs on one trunk and other Vlans on another trunk without causing a Spanning Tree loop.

PVST+ : Per-VLAN Spanning Tree plus
Per VLAN Spanning Tree Plus (PVST+), an enhancement to the 802.1Q specification and unsupported on non-Cisco devices, maintains a spanning tree instance for each VLAN configured in the network. PVST+ is a new version of PVST, uses ISL Trunking and allows a VLAN trunk to be forwarding for some VLANs while blocking for other VLANs. Since PVST treats each VLAN as a separate network, it has the ability to load balance traffic (at layer-2) by forwarding some VLANs on one trunk and other Vlans on another trunk without causing a Spanning Tree loop.

PXE: Preboot Execution Environment
Preboot eXecution Environment (PXE), a specification published by Intel and Systemsoft, is an environment to bootstrap computers using a network interface card independently of available data storage devices (like hard disks) or installed operating systems. It makes use of IP, UDP, DHCP, TFTP, GUID/ UUID, UNDI (Universal Network Device Interface) and extends the PXE client's (the computer to be bootstrapped via PXE) firmware with a set of predefined APIs.