RADVISION术语表

Glossary (P)

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O- P - Q - R - S - T - U - V - W - X - Y - Z

PACKET
A block of data used for transmission in packet-switched systems.

PACKET LOSS
In packet communications, when packets do not arrive at their destination. The higher the packet loss, the lower voice or video quality. Packet loss is typically measured in percentage of packets lost versus the total number of packets sent by the source. There can be various reasons for packet loss, such as noise on the communication channels, transmission errors, higher packet rate than available throughput, and more. Also some devices might not have adequate buffers or CPU power to handle incoming packets, and as a result some may be intentionally discarded by the device, the network or in between.

PACKET REORDERING
Packet reordering ensures that all packets reach their destination in the correct sequential order. An event of packet disordering can occur when two packets belonging to one stream take different routes to their destination, such that a packet sent later than its peer may arrive to the destination earlier.

PACKET SWITCHING
A networking technology that routes messages according to layer-2 headers to their required destination.

PARENT FILTERS
When a Gatekeeper fails to resolve a destination address, the Gatekeeper searches for the destination first among its Children, then among its neighbors and then via its parent. Parent filters enable the Gatekeeper to avoid unnecessary searches among its Children and Neighbor Gatekeepers.

PARTY NUMBER
The dialing number of an endpoint. This number can be a telephone number or a number used by other mechanisms on various networks, such as telex and ISDN.

PBX (PRIVATE BRANCH EXCHANGE)
A small or medium company-owned telephony switching system. Used to enable direct dialing between endpoints on the corporate LAN, or for long-distance direct dialing between endpoints.

POC (PACKETS OVER CELLULAR)
See Push To Talk Over Cellular

POINT-TO-POINT
Communication configuration in which communication is between two stations only. Contrast with multipoint.

POLICY
An ordered combination of policy rules that defines how to administer, manage, and control access to resources.

POP (POINT OF PRESENCE)
The point at which a line from a long distance carrier connects to the line of the local telephone company, or to the user if the local company is not involved. For online services and Internet providers, the POP is the local point into which users access the Internet.

PORT
A pathway into and out of a computer or a network device, such as a switch or router.

PORTAL
An entity that aggregates access to services and content for easy reach to customers, including service level authorization and single sign on (SSO) functions.

POST PAY BILLING
Billing arrangement between subscribers and service providers where the subscriber periodically receives a bill for service usage in the past period.

POTS (PLAIN OLD TELEPHONY SERVICE)

PREDEFINED ENDPOINT
An endpoint entitled to register with a specified Gatekeeper.

PREFIX
A prefix is a part of the dialing sequence used to access a service or conference type. See also Gateway Supported Prefixes and Conferencing Service

PREPAY BILLING
Billing arrangement between subscriber and service provider where the subscriber deposits an amount of money in advance, which is subsequently used to pay for service usage.

PRESENCE INFORMATION
In computer and telecommunications networks, presence information conveys status on a party’s a availability and willingness to communicate. A client publishes presence information to other systems’ users to convey its communication state. Presence information has wide applications in voice over IP and instant messaging.

PRI (PRIMARY RATE INTERFACE)
An ISDN subscriber interface supporting 23 bearer B channels at 64 Kbps and two data D channels at 16 Kbps (in North America), or 30 bearer B channels at 64 Kbps and two data D channels at 16 Kbps (in Europe). A PRI connection runs at 1.544 Mbps per second over a T-1 connection, and at 2.048 Mbps per second over an E-1 connection.

PROXY SERVER
An application that breaks the connection between sender and receiver. All input is forwarded out on a different port, closing a straight path between two networks and preventing a hacker from obtaining internal addresses and details of a private network.

PSTN (PUBLIC SWITCHED TELEPHONE NETWORK)
The worldwide voice telephone network. Once only an analog system, most telephone networks today are digital. In the US, most of the remaining analog lines are the ones from your house or office to the telephone companyís central office.

PUSH TO TALK OVER CELLULAR
A walkie-talkie type service provided over a cellular phone network. The application uses the packet network for instant one-to-one conversations.