X25AM Configuration and Management Manual

Glossary
X25AM Configuration and Management Manual—523424-004
Glossary-7
packet assembler/disassembler (PAD)
packet assembler/disassembler (PAD). Device that enables an asynchronous terminal or
personal computer to access a PSDN. It assembles or disassembles communications
packets. The device serves as an interface between a terminal or computer and a
packetizing network. It can be hardware or software.
packet level. X.25 protocol description for packet formats and transmission of data across
the link between the network and the computers, terminals, or other devices.
packet size. Number of bytes of user data in a data packet.
packetizing. Procedure by which a message is broken up into packets for transmission in a
packet-switching network.
packet switching. Method for transmitting information in packets in a network.
packet-switching data network (PSDN). A network providing packet-switching data
communications services. A PSDN can be either a public data network (PDN) or a
private packet-switching data network.
packet-switching exchanges. Computers in a packet-switching network.
PAD. See packet assembler/disassembler (PAD).
PAD profile. Group of PAD parameter settings.
page. Unit of memory consisting of 2048 bytes.
parity bit. Bit appended to a group of bits making an odd number of ones in the group (odd
parity) or an even number of ones in the group (even parity.)
parity checking. Testing a group of bits to determine whether the number of ones in the
group is odd or even.
PDN. See public data network (PDN)
.
permanent virtual circuit (PVC). Association between two entities for packet exchange. A
call consists of data transfer and does not require call setup and call clearing.
physical level. X.25 protocol description for the physical link between the network and the
computers, terminals, or other devices.
port number. Number assigned to a subdevice to link an address to a specific subdevice.
Sometimes referred to as a subaddress.
primary station. In an SDLC or ADCCP-NRM configuration, the primary station initiates a
data transfer and is in control during the exchange of messages. The primary station
notifies each secondary link station when the secondary station can transmit data and
when it should expect to receive data. This type of configuration is not used for X.25
connections. However, the combined station used for X.25 connections is logically