| Packet | a unit of data, usually consisting of several bytes, transmitted over a packet network |
| Packet Assembly/Disassembly Device (PAD) | device which permits terminals which do not have an interface suitable for direct connection to a packet switched network to access the network |
| Packet Switch Exchange (PSE) | unit which performs packet switching in a network |
| Packet Switching | data transmission technique that divides messages into standard sized packets for routing and transport through a network |
| Parental lock | consumer satellite TV receiver's PIN operated lock which allows parents to prevent children from watching channels with an adult content |
| Parity bit | a binary digit added to a character or block to make the number of 1's always odd (odd parity) or always even (even parity) |
| Parity check | error checking technique which tests whether the number of 1's in a received group of binary digits is odd (for odd parity) or even (for even parity) to determine whether the received data has errors |
| Payload | part of a satellite which performs the primary function for which the satellite was designed; in a communications satellite the payload consists of the communications equipment which receives, processes and retransmits the required channels |
| Payload | part of a message, block or packet of data which contains the intended data, rather than headers, error checking words, etc |
| Pay Per View (PPV) | a payment system for TV broadcasts in which the viewer pays to watch a specific item |
| Payphone | public telephone at which calls may be made with payment made by coins, phone cards, credit cards or by reversing charges |
| Pay TV | television channel requiring the payment of a subscription for reception |
| Perigee | the nearest point on a satellite's orbit to the Earth |
| Period | the time taken by a satellite to complete one orbit |
| Permanent virtual circuit (PVC) | a connection between two terminals which is always available without call set up being required |
| Phase Modulation (PM) | the technique of changing the phase of a carrier wave in proportion to the strength of a baseband signal |
| Phasing orbit | a temporary orbit used prior to the injection of a satellite into its final orbit |
| Piracy | unauthorised access to controlled transmissions |
| Piracy | the unauthorised use of transmission systems (ie by unlicensed broadcasters) |
| Point to point link | one or two-way connection between two nodes |
| Polarisation plane | plane which contains the E-wave of an electromagnetic wave |
| Polarisation rotator | a device which can select one of two orthogonal polarisations, operation may be manual or may be controlled electronically |
| Polar Orbit | an orbit with inclination i=90° |
| Polling | a means of regulating communications on a channel by sequentially asking each node if it has any traffic to send |
| Positioning | technique of determining the location of an object or vehicle by triangulation from ground or satellite based beacons |
| Pre-assigned multiple access | a multiple access system in which earth stations are permanently assigned transmission channels |
| Prime focus | the point where a lens or dish brings waves to a focus |
| Prompt | character that alerts the user that a device is ready to accept input |
| Propagation delay | time taken for a signal to travel from the sender to the receiver |
| Propellant | the fuel or oxidant used by a satellite or launch vehicle; propellants can be solid or liquid |
| Protected use transponder | a transponder on which users are guaranteed that their traffic will be switched to another transponder, should the transponder fail |
| Protocol | set of standard procedures that allow devices to intercommunicate |
| Protocol converter | a device for translating the data transmission code and/or protocol of one network or device to the corresponding code or protocol of another network or device, enabling equipment with different conventions to communicate together |
| Protocol stack | the related layers of protocol software that function together to implement a particular communications architecture |
