System information

System Administration Guide

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Revised: March 28, 2007

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10 Digital Lines

The digital lines feature set is specific to Allworx products that have built in T1 interfaces such as the Allworx

24x. This feature is not available on other Allworx server products.

10.1 Introduction

Allworx refers generically to the integrated T1 interfaces as Digital Lines. For example, on the Allworx 24x

product there are two T1 Digital Line interfaces. These interfaces are accessed through the connectors

labeled T1-A and T1-B respectively. The T1-A interface can operate as a Primary Rate ISDN line and/or as a

T1 data line for connectivity to another site or to an Internet Service Provider. That is, the T1-A interface

supports both circuit switched voice calls and TCP/IP data. The T1-A interface also supports Robbed Bit

Signaling (RBS) operation. The T1-B interface is dedicated for use as a data connection. The data

connection can be used for connectivity to another remote site on a dedicated T1 line or for connectivity to a

service provider for Internet access.

10.1.1 PRI Support

The T1-A interface supports Primary Rate ISDN using the National Standard ISDN format (NI-2), Lucent

Custom 4ESS, Lucent Custom 5ESS, and Nortel DMS-100 switch types. The Allworx server ISDN interface is

always configured as the user side equipment with the intention of hooking to the service provider’s Central

Office (CO) network side equipment. The Allworx server interfaces have a fully integrated CSU/DSU and are

typically intended for direct short haul connection to the service provider’s smart jack. Consult the product

installation instructions for further information.

Note: When PRI operation is desired it is important to define exactly one PRI D-Channel for the Digital Line

and a minimum of one PRI B-Channel. The configuration must 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.

10.1.2 Robbed Bit Signaling (RBS) Support

The T1-A interface 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). Currently, as of

the 6.5 software release, the following modes are supported:

 FXO Loop-Start

 FXO Ground-Start

 E&M Wink Start Feature Group B (single wink)

 E&M Immediate Start

For the above selections, operational use is basically 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, it is not guaranteed 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