ISDN/RBS Trunk Busy-Out Feature Guide

Overview

With the release of AOS 16.01, AOS voice devices support the capability to actively disable a PRI or E&M/RBS trunk based on an IP connectivity test. This feature can be used to notify a local PBX that connectivity to a SIP trunk has been lost so the PBX can attempt to route calls in an alternate direction.

This feature utilizes network-monitor. For more detail, please see this guide:

Configuring Network Monitor in AOS

Configuration Steps

1.  Create a probe

Configure a probe that will monitor your primary data connection in order verify that it's still active. Usually an icmp-probe is the simplest option here, and sending a ping directly to your softswitch would obviously be the best target, assuming your softswitch accepts ICMP. From global configuration mode:

!

probe drop-trunk icmp-echo

  destination 192.168.1.1

  period 5

  tolerance consecutive fail 3 pass 2

  no shutdown

!

This probe, named "drop-trunk", sends an icmp echo-request to 192.168.1.1 every 5 seconds. If the probe fails to receive 3 consecutive responses, the probe will enter a FAIL state. Two consecutive responses will  put the probe back into a PASS state. Adjust the period and tolerance values as needed. The command ‘show probe’ can be used to see the probe’s current status.

2. Create a track that references the probe

!

track test-track

  test if probe drop-trunk

  no shutdown

!

This track, named "test-track", simply watches the probe and determines whether or not it's in a failed or passed state. The track is listed separately because you can reference multiple probes in a single track.  The command "show track" will let you see the configured track’s status.

3. Configure ‘busy-out’ on RBS or ISDN voice trunk

For PRI:

!

voice trunk T02 type isdn

  busy-out monitor track test-track

  connect isdn-group 1

!

or for RBS:

!

voice trunk T03 type t1-rbs supervision wink role network

  busy-out monitor track test-track

  connect t1 0/2 tdm-group 1

!

Sample Debugs

PRI

When the track fails on an ISDN trunk, the busy-out option will take down the D channel.

NETMON.PROBE drop-trunk: value changed to fail

NETMON.PROBE drop-trunk: Request timed out. (failed)

NETMON.TRACK test-track: Controlling account T02 New state: FAIL

NETMON.TRACK test-track changed from pass to fail.

ISDN.EP PRI 1 D channel is DOWN

INTERFACE_STATUS.pri 1 changed state to down

NETMON.PROBE drop-trunk: Request timed out. (failed)

The D channel negotiation resumes when the track returns to a passed state.

NETMON.PROBE drop-trunk: Reply from 192.168.1.1: bytes=92 time=14ms (passed)

NETMON.PROBE drop-trunk: value changed to pass

NETMON.PROBE drop-trunk: Reply from 192.168.1.1: bytes=92 time=12ms (passed)

NETMON.TRACK test-track: Controlling account T02 New state: PASS

NETMON.TRACK test-track changed from fail to pass.

ISDN.L2_FMT PRI 1 ======================================

ISDN.L2_FMT PRI 1 Sent = Sapi:00 C/R:C Tei:00

ISDN.L2_FMT PRI 1 Ctl:SABME

ISDN.L2_FMT PRI 1 ======================================

ISDN.L2_FMT PRI 1 Recd = Sapi:00 C/R:C Tei:00

ISDN.L2_FMT PRI 1 Ctl:UA

ISDN.EP PRI 1 D channel is UP

INTERFACE_STATUS.pri 1 changed state to up