Why has a Cisco TelePresence Video Communication Server (Cisco VCS) cleared an H.323 call involving a Lifesize endpoint?
This issue may affect calls passing through a Cisco VCS that are between a Lifesize endpoint running software version 4.0 or earlier, and any other devices (including MCUs and gateways) that are not Cisco TelePresence or Polycom endpoints.
The issue occurs due to a bug in the Lifesize code. The bug was due to be fixed in Lifesize version 4.1.
The work-around is to increase the value of the Call time to live setting on the Cisco VCS, although this is not necessarily recommended because it will increase the amount of time taken by the Cisco VCS to recognize and clear any hung calls.
A Cisco VCS will periodically query the endpoints in a call to ensure that they are still participating in that call. It does this by sending the endpoint an IRQ message, to which the endpoint must respond. If one or more of the participants is no longer in the call, Cisco VCS will clear the call so that the call is not left "hanging". The frequency with which the Cisco VCS queries the endpoints is determined by the Call time to live setting in the Gatekeeper section of the H.323 page (VCS configuration > Protocols > H.323). The default is 120 seconds.
Lifesize endpoints prior to version 4.1 respond to the IRQ query sent by the Cisco VCS, but the reply does not include any information about the call they are currently in (contrary to the H.323 V4 standard). The Cisco VCS therefore considers the endpoint to be no longer in the call, and so clears the call.
The work-around for this is to increase the H.323 Call time to live setting on the Cisco VCS (VCS configuration > Protocols> H.323) to a value greater than the length of the majority of calls that take place in your network. This will stop the Cisco VCS from checking that the endpoints are in a call during this time.
changing the H.323 Call time to live
setting on the Cisco VCS will affect the frequency with which the Cisco VCS queries all H.323 devices in a call, not just the Lifesize endpoints, and will increase the amount of time taken by the Cisco VCS to recognize and clear any hung calls.
This article applies to the following products:
- Cisco Video Communication Server
|June 16th, 2011||TAA_KB_436|