CAC On Voice Gateway/CME part 3

To read part 1 , click here

To read part 2 , click here

To read part 3 , click here

To read part 4 , click here

Advanced Voice Busy out (AVBO)

In the figure below , legacy PBX in the main site is connected via BRI card to a Cisco voice Gateway. when calling a remote site, priority path will be through the Cisco Voice Gateway secondary path will be through the PSTN.

The idea of this method is to test the voice quality , if it is ok we will accept calls on the BRI interface , if for any reason we have a bad quality we will provoke a busy tone on the BRI interface allowing the PBX to use its secondary path


Cisco2821(config)#voice-port 0/0/0
Cisco2821(config-voiceport)#busyout monitor probe 192.168.30.1 codec g729ar8 icpif 15

0/0/0 is the BRI port connected to the legacy PBX

probe : The RTR probe sends a burst of packets to the RTR responder. The RTR responder turns them around and sends them back to the probe. This simple operation allows the probe to measure packet loss and round trip delay. To measure jitter, the probe sends a control packet to the responder before it initiates the packet burst. The control packet informs the responder how many milliseconds (ms) to expect between each packet in the burst. The responder then measures the inter-packet delay during the burst, and any deviation from the expect interval is recorded as jitter

In another words (my words) : the probe will simulate voice packets , but it has small size , it will come back to the voice gateway and give a result of the quality , lost , jitter …

192.168.30.1 is the ip address of the CME , the codec that will be used is g729 Annex A


So to resume , under the BRI port , the voice gateway will play the busy tone whenever the voice quality to the CME remote site exceed 15 , to find more about the voice quality see the table below

Table 1 Quality Levels as a Function of Total Impairment Factor ICPIF

Upper Limit for ICPIF Speech Communication Quality
5 Very good
10 Good
20 Adequate
30 Limiting case
45 Exceptional limiting case
55 Customers likely to react strongly (complaints, change of network operator)

Ref:http://www.cisco.com/en/US/docs/ios/12_4/ip_sla/configuration/guide/hsvoipj.html

Ref:http://www.cisco.com/en/US/tech/tk648/tk362/technologies_tech_note09186a0080094b26.shtml

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This entry was posted in CallManager Express, Gateway, LAB and tagged , , , . Bookmark the permalink.

3 Responses to CAC On Voice Gateway/CME part 3

  1. Pingback: CAC On Voice Gateway/CME part 4 | elhallak

  2. Pingback: CAC On Voice Gateway/CME part 2 | elhallak

  3. Pingback: CAC On Voice Gateway/CME part 1 | elhallak

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