ISDN Overview

The IMG 2020 supports (ISDN) Integrated Services Digital Network for a complete digital telephone/telecommunications network which will carry voice, data, and video over an existing telephone network. The IMG 2020 supports 128 Kbps high-speed and high-bandwidth service. ISDN non-compressed (512 Kbps compressed) can also provide on-demand service and can connect up to eight devices simultaneously with each device being call-managed.

• Supports up to 32 D channels. Each D channel provides the High Data Link Control (HDLC) communications over T1, E1, DS3, or STM-1 on one time-slot on the span.

• The basic configuration is 23B+D (Primary Rate Interface) and 30B+D outside of North America.

• Interfaces with various equipment types supporting the ISDN PRI protocol including tandem (Class 4) switches and end office (Class 5) switches.

• The IMG 2020 ISDN PRI implementation is based on ITU-T Q.921 and Q.931 specifications. Each implemented variant references the appropriate interface document supplied by the equipment manufacturer. The interface document is usually a variant of the ITU-T recommendations.

• The IMG 2020 supports one D channel per span [Facility Associated Signaling (FAS)], or one D channel managing up to 20 spans [Non-Facility Associated Signaling (NFAS)].

• (NFAS) Each D channel on the IMG 2020 can control up to 19 other spans in addition to the span on which it is located.

• Connection endpoint variants are defined for National ISDN as User side and Network side. You can intermix both FAS and NFAS D channels with each supporting a different variant.

• Supports sending UUI (User to User Information) between called and calling parties during the Setup, Clearing, and Active Phase of the Call. The User to User Information support passes specific information not pertaining to the call from one user to another.

• Interworking between ITU ISUP and ISDN follows the Q.699 recommendation.

• Interworking between ANSI ISUP and ISDN follows the T1.609 recommendation

• Fallback procedures are not supported hence any interworking related to fallback is not supported.

• Supplementary services are not supported.

• Supports Interwork ISDN DISC with Progress Indicator to SIP 183 with SDP. Upon receiving ISDN DISC with progress indicator, IMG 2020 will complete the call setup then cut through to establish the early media session, in order to relay an audio announcement. Once the early media session is established, the call can be torn down by the ISDN side (after announcement has ended) or by the SIP side (hang up).

D-Channel Backup

The IMG 2020 supports the D-Channel backup procedure as defined by Lucent TR 41459. This procedure provides a standby D-Channel when using NFAS. When an active D-Channel fails, or if there is a span alarm, the IMG 2020 converts to the standby D-Channel and maintains active calls. This is a provisioned option and is applicable only when using NFAS. D-Channel backup is supported on the T1 only.

The IMG 2020 supports Implicit Mode for ISDN NFAS D-Channel Backup. This will support the case when the interface identifier is not present and the D-Channel backup is used for signaling.

NFAS

NFAS is supported over T1 with the NI-2, 4ESS/5ESS, and DMS 100/250 variants. It is not supported over E1 with the Euro ISDN variant, or over T1 with the JATE variant. 

Supported Variants

Features