Introduction to Tandem X.25 Capabilities

Glossary

Glossary–8 065307 Tandem Computers Incorporated

physical level. X.25 protocol description for the physical link between the network and

the computers, terminals, or other devices.

physical unit (PU). An entity in an SNA network, responsible for the physical

configuration of a node. Often identified with the node itself: for instance, a host is a

PU type 5.

point-to-point. A data link configuration between only two stations. The X.25 standard

supports only point-to-point communications. In other types of communications, such

as SNA or BSC, it is possible to have multipoint configurations. In multipoint

configurations, one station is designated as a supervisor controlling multiple tributary

stations.

port number. Number assigned to a subdevice to link an address to a specific subdevice.

Also referred to as a subaddress. Port does not refer to a physical component; it refers

to the logical mapping of the subdevice to the address.

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 divided into a primary substation and a secondary substation.