Packet. A specific number of bits of data sent over a link in a packet switched network. A packet contains the data and control information needed for the successful delivery of the packet to the desired address. The terms packet and frame are often used interchangeably.

Packet switching. A means for transmitting data messages by dividing the message into blocks or packets of standard length. Each packet has the destination address and other control information coded into it.

PAD (Packet Assembler and Dis-assembler). A PAD assembles packets of asynchronous data and sends these buffers in a burst to a packet-switched network. The PAD also disassembles packets from the network and sends the data to the non-packet device.

Paging. A one-way message that tells the subscriber that their attention is required.

Parity. A check for alterations in transmitted data.

Party. A participant in a call, for example, a called party (also known in telephony as the b-subscriber) and the calling party (also known in telephony as the a-subscriber).

PAT (Program Association Table). A DVB/MPEG-2 PSI table that contains a list of all programs in the TS.

Path loss. The attenuation of a radio signal, for example, as the mobile station moves away from the base transceiver station.

Payload. The part of an ATM cell that contains the information being sent.

PCS-1990. The U.S. variant of the European Global System for Mobile Communications (GSM) digital cellular standard that operates at 1900 MHz.

PCN. Personal Communciations Network. A wirless telephone system requiring low-power transceivers.

PCR (Program Clock Reference). A DVB / MPEG-2 reference clock used in synchronizing the transmission of one Program Stream.

PCH (Paging Channel). The PCH is a special channel reserved within a cellular mobile phone network for paging or alerting mobile terminals to an incoming call.

PDA (Personal Digital Assistant).

PDC (Personal Digital Cellular). PDC is the second generation digital cellular standard developed for use in Japan.

PDC MAP: PDC Mobile Application Part. PDC MAP is the core network that supports the PDC standard.

PDH (Plesiochronous Digital Hierarchy). PDH (plesiochronous means nearly synchronous), was developed to carry digitized voice over twisted pair cabling more efficiently. This evolved into the North American, European, and Japanese Digital Hierarchies where only a discrete set of fixed rates is available, namely, nxDS0 (DS0 is a 64 kbps rate) and then the next levels in the respective multiplex hierarchies.

PDU (Protocol Data Unit). A PDU is a message of a given protocol comprising payload and protocol-specific control information, typically contained in a header. PDUs pass over the protocol interfaces which exist between the layers of protocols (per OSI model).

PES (Packetized Elementary Stream). A DVB / MPEG-2 bit-stream consisting of variable length packets of digitized video or audio Elementary Streams, or data.

Physical layer. The first layer of the OSI model, which represents the hardware used for communication.

PID (Packet Identification). Identifies the packet types within the DVB/MPEG-2 TS, in order to assist the decoder in identifying individual programs and their associated components. It does this in conjunction with the PSI tables.

PIN (Personal Identification Number). A secret number that the subscriber enters in the mobile terminal to get access to the network.

Pixel. The individual picture elements that form an image.

PLMN Service Area. The geographical area served by a single network operator.

PMT (Program Map Table). A DVB/MPEG-2 PSI table that is referenced from the PAT and identifies components and features for each program.

PN (Pseudo-Noise). A PN signal is a deterministic signal that has certain noise-like characteristics with regard to randomness and autocorrelation properties.

Polar mount. Allows a satellite antenna dish to follow a segment of the geostationary arc, by rotating around just one axis.

Polling. The transmission of a signal from the BTS to the mobile station to find out if the mobile station is still within the vicinity of the BTS.

Port. The point of entry to or exit from a network.

Port Identifier. The identifier assigned by a logical node to represent the point of attachment of a link to that node.

Powered off. The status of a mobile telephone that is not switched on.

PRBS (Pseudo-Random Binary Sequence). A PRBS is a binary PN signal (that is, a sequence of binary 1's and 0's that exhibits certain randomness and autocorrelation properties).

Presentation Layer. The sixth level of the OSI model, which is concerned with the presentation of data at the receiving end of the link.

Protocol. A guide to formal interactions. Protocols are agreed recommendations and standards that describe how systems communicate (inter-operate) with each other.

PS (Program Stream). A DVB / MPEG-2 multiplex of Packetized Elementary Streams from one program, using the same Program Clock Reference. Several PSs can be combined into one Transport Stream.

PSI (Program Service Information). A DVB/MPEG-2 set of tables which enable individual TV programs and their components to be identified.

PSTN (Public Switched Telephone Network). The PSTN is the traditional fixed line telephone network.

PT (Payload Type). A 3-bit field in the ATM cell header that discriminates between a cell carrying management information or one which is carrying user information.

PVC (Permanent Virtual Circuit). A link with static route defined in advance, usually by manual setup.

PVCC (Permanent Virtual Channel Connection). An ATM connection where switching is performed on the VPI/VCI fields of each cell. A Permanent VCC is one which is provisioned through some network management function and remains indefinitely.

PVPC (Permanent Virtual Path Connection). An ATM connection where switching is performed on the VPI field only of each cell. A Permanent VPC is one which is provisioned through some network management function and remains indefinitely.