Understanding ISDN PRI Support for Voice Traffic

SRX210 and SRX240 devices running Integrated Convergence Services support basic analog interfaces FXS and FXO, the digital interface T1, and SIP endpoints for voice over IP (VoIP). T1 support provides flexibility by implementing multiple trunks, but it is expensive. A T1 line must be leased for voice calls, even if voice is used for only some of the available time slots.

A channelized T1 ISDN Primary Rate Interface (ISDN PRI) creates the equivalent of a 24-channel T1 line and is popular for connecting public switched telephone network (PSTN) circuits to PBXs. It provides scalability with the flexibility to set up calls on an as needed basis. In other words, you pay only for what you consume.

With ISDN PRI you can configure multiple channels on a single T1 line. Each time slot or bearer channel (B-channel) can be configured independently or a group of B-channels can be part of a single PRI call.

The current T1 Mini-Physical Interface Module (Mini-PIM) supported on SRX210 and SRX240 devices running Integrated Convergence Services is not channelized. ISDN PRI requires channelized T1 support. However, the current T1 Mini-PIM can be configured to provide virtual channels for voice only, even though it is not channelized. With this implementation, the T1 Mini-PIM on these devices operates like a channelized Mini-PIM and provides ISDN PRI support for voice channels.

Note: The ISDN PRI implementation on SRX210 and SRX240 devices running Integrated Convergence Services is limited to voice only. Data traffic cannot be supported on any channel.

On these devices, the T1 Mini-PIM can be configured either as a single clear-channel T1 interface or as a channelized T1 ISDN PRI interface with up to 23 B-channels for voice and 1 D-channel for signaling.

Related Topics

• SRX Series Integrated Convergence Services Media Gateway Overview
• Understanding the SRX Series Integrated Convergence Services Media Gateway
• Understanding the SRX Series Survivable Call Server