Glossary of Terms and acronyms

Packet Switching:
Data transmission method that divides messages into standard-sized packets for greater efficiency of routing and transport through a network. Internet consists of a series of packet switching networks.

PCTV:
Concept of personal computer integrated with the function of a TV set. Generally considered to be dependent on the availability of new flat screen displays rather than the conventional cathode ray tube.

Peering:
This is the physical exchange of data traffic between ISP and another. Peering arrangements are a long standing practice among ISPs by which they consent to exchange traffic without charge, based on mutual benefit. Normally peering is undertaken at public peering points such as the London Internet Exchange (LINX).

Pencil Beam:
Satellite downlink beam which covers only a very small geographic area, perhaps no more that a couple of hundred kilometres across, as distinct from spot beams which tend to cover whole countries or regions.

Point-to Point Link:
A satellite link that is intended to provide communications between two fixed points even though the satellite downlink can be received anywhere within its footprint. A point to multipoint link is intended to be received at many sites within the downlink beam. Examples of the former are telephone circuits carried on a satellite. The commonest form of the latter is a satellite TV signal.

Polar Orbit:
An orbit with its plane aligned in parallel with the polar axis of the earth.

PTT:
Post Telephone and Telegraph Administration. Refers to operating agencies directly or indirectly controlled by governments in charge of telecommunications services in most countries of the world.

Pulse Code Modulation:
A time division modulation technique in which analogue signals are sampled and quantized at periodic intervals into digital signals. The values observed are typically represented by a coded arrangement of 8 bits of which one may be for parity.