User guide

System Administrator’s Guide – Release 7.5
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Revised: April 9, 2013
Page 111
match the provisioning defined by the Central Office with a typical configuration
having 23 B channels on slots 1 through 23 and one D channel on slot 24.
13.4.4 NFAS Support
Non-Facility Associated Signaling (NFAS) is a PRI where multiple T1 lines share the
same D channel. The Allworx server supports NFAS using the National Standard
ISDN, Lucent Custom 4ESS, Lucent Custom 5ESS, Nortel DMS-100 switch types.
Note: The configuration must match the provisioning defined by the Central Office. A
typical configuration has 23 B channels on slots 1 through 23 and one D channel
on slot 24 of the primary T1 line, plus 24 B channels on slots 1 through 24 of the
secondary T1 line. To configure NFAS on the Allworx system, connect the NFAS
line with the D channel to the T1-A port.
13.4.5 Robbed Bit Signaling (RBS) or Channel Associated
Signaling (CAS) Support
The Allworx server supports classical T1 Robbed Bit Signaling (RBS) trunk lines on a
time slot by time slot basis. Sometimes this functionality is referred to as T1 Channel
Associated Signaling (CAS). The following modes are supported:
• FXO Loop-Start
• FXO Ground-Start
• E&M Wink Start
• E&M Feature Group B
• E&M Immediate Start
For the above selections, operational use is the same as the corresponding analog
interface types. The precise signaling protocols for each interface are implemented in
conformance with the procedures documented in EIA/TIA-464C. Inbound Caller-ID is
supported on the FXO modes, if the CO supports it and the check box is enabled on
the Outside Lines > Digital Lines > Modify page.
For primary CO line connectivity, the FXO Ground-Start slot choice is typically
preferred to minimize the possibility for glare conditions, especially when call volume is
high. Furthermore, Allworx does not guarantee that the network provides an explicit
disconnect signal in FXO Loop-Start mode. Normally, the user would terminate a call
by hanging up the phone. However, if a call is under the supervision of the auto-
attendant, the lack of a terminating signal can cause a call to remain live for an
extended period of time (tens of seconds) after the call should be dead. Some FXO
lines support a supplemental feature known as line-side answer supervision where the
network provides an explicit signal acknowledging that the far end has picked up
during an outbound call. Because not all network equipment can produce this state,
calls cannot rely upon it and ignores the state.
Neither of the FXO modes supports Direct Inward Dialing (DID). However, the E&M
modes do support DID, and are required if DID operation is desired. The other
advantage of the E&M modes is that both of them are symmetrical protocols and can