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UC540 and max-conn in SIP trunk

Hello,

  For some kind of poor redundancy, we have two UC540 IPBX on the same site and in the same network. They are linked each other with a sip trunk as shown below.

  IPBX A <-- SIP Trunk --> IPBX B

  SIP Trunk on IPBX A

  ------------------------------

  dial-peer voice 10 voip

    max-conn 10

    destination-pattern 4...

    session target ipv4:192.168.1.40

    max-redirects 10

    dtmf-relay h245-alphanumeric

    codec g711ulaw

    no vad

  SIP Trunk on IPBX B

  ------------------------------

  dial-peer voice 20 voip

    max-conn 10

    destination-pattern 3...

    session target ipv4:192.168.1.41

    max-redirects 10

    dtmf-relay h245-alphanumeric

    codec g711ulaw

    no vad

  Users says there are some drop calls quite often between these two ipbx, especially during external call transfer.

  Could anyone could tell me how much SIP connections in the trunk can each ipbx support ? Also what is the best way to monitor theses drop calls in order to identify the root cause of it ?

Thanks in advance

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UC540 and max-conn in SIP trunk

I don't think there are hard limits.  I mean you've got hard and fast limits of dsp's, and you've defined max-connection limits on those dial-peers, but as far as the number of call legs that a device can terminate...  There are a lot of factors at play.  It depends on what else you're doing on that device.  Cisco might have published some best practice type numbers around the UCxxx boxes but I haven't seen them (I haven't searched exhaustively though).  You haven't mentioned which IPBX you're using, but you've got some hard upper caps based on the software/hardware you're using for those as well.

Those 2 dial-peers do limit you to10 calls from A - B and 10 calls from B - A however but wouldn't cause an in-progress call to drop but could cause a transfer/conference attempt to fail.  I'm assuming that you don't have CAC in place.  You could use RTMT and UCM traces, but since you've got a UBE I'd just run a sip message debug.  The output is very readable and you should be able to see what's happening pretty easily.

hope that helps,

will

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