Description: The SAP table contains configuration information for each X.25 layer SAP (service access point).

Service Access Points

Two types of SAPs exist:

- Upper: A SAP that exists at the upper interface of the X.25 layer and serves an embedded application.

- Lower: A SAP that exists at the lower interface of the X.25 layer and serves a single data link connection (LAPB) or multiple data link connections (LAPD).

This data link connection, when attached to the sub-layer, can complete a LAPB service, or can be one of many supported data link connections over a LAPD service.

SAPs are identified by a SAP Number and CES (connection endpoint suffix).

X.25 LAPB service supports only one data link connection and thus only one SAP is required. Its CES is irrelevant and is normally set to 0 at this SAP. This SAP communicates with its 'companion' SAP at the sub-layer in a one-to-one relationship.

X.25 LAPD service supports multiple data link connections, and thus multiple SAPs are required. The CES for each must be unique and is normally in the range of 0 to 63. Each of these SAPs (which are grouped according to SAP Number) communicate with the same 'companion' SAP at the sub-layer in a many-to-one relationship.

Facilities

This table contains numerous facilities subscription parameters. Each facility subscription that is part of the standard, is referenced to the appropriate section in the ITU(CCITT) X.25 (1988) blue book in the REFERENCE section of the object.

Terms used in this table

Incoming calls: For lower SAPs, these are the X.25 calls received from the sub-layer. For upper SAPs, these are the X.25 calls received from the associated application.

Outgoing calls: Are the X.25 calls routed from other SAPs, which are to go out this SAP.

Source side: The side that received an incoming call.

Destination side: The side that will send the outgoing call.