1.3.7. [NFAS] Section

Non-Facility-Associated Signaling (NFAS) uses a single ISDN PRI D channel to provide signaling and control for up to 10 ISDN PRI lines. Normally, on an ISDN PRI line, one D channel is used for signaling and 23 B channels (bearer channels) are used for transferring information. In an NFAS configuration, therefore, one D channel can support the signaling and control for up to 239 B channels. The trunk that provides the signaling is called the primary D channel. The trunks that use all 24 channels as B channels are called NFAS trunks.

Notes:

1. For a board containing multiple primary D channels, the maximum number of trunks supported by each NFAS group on that board is reduced. This is due to the additional message load on the board's CPU.
2. NFAS is only supported by the NI2, 4ESS, 5ESS and DMS protocols.

The CONFIG file contains an [NFAS] section and multiple [NFAS.x] sections. The [NFAS] section defines the number of NFAS instances created, that is, defines the number of NFAS groups. For each NFAS group, there is an [NFAS.x] section in the CONFIG file. For example, if there are two NFAS groups defined in the [NFAS] section, there will be two [NFAS.x] sections, [NFAS.1] and [NFAS.2].

NFAS parameters are modified by editing the respective lines in the [NFAS] and [NFAS.x] sections of the CONFIG file. For example, to increase the number of NFAS groups per board from one to four, change the value of NFAS_INSTANCE_MAP (parameter = 0x3e02) from a value of 1 (one group per board) to a binary value of 1111 (four NFAS groups per board) represented by 0xf.

Following is an excerpt from the [NFAS] section of a CONFIG file that illustrates that part of the file before and after editing.

Before editing:

[NFAS]
SetParm=0x3e02,0x1 !INSTANCE MAP, default = 1 (1 group/board) 

After editing:

[NFAS]
SetParm=0x3e02,0xf !INSTANCE MAP - 4 NFAS groups/board 

Also, when NFAS is used, the SignalingType parameter in the [lineAdmin] section of the CONFIG file must be modified. For details about this parameter modification, see Section 4.6.2, SignalingType (Signaling Type).

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