CME to CME Call forward loop

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Sample call flow of such scenario-
IP Phone CME A >> IP Phone CME B >> Call forward to another extension of CME B.
In call forward loop scenario, Call will reroute by CME A instead of CME B.
This scenario gets complicated when we call forward the calls to a PSTN number, in such scenarios, call routes via CME A, still doesn't looked complicated, let me give you an example-

India IP phone calling directly to US IP phone which is CFA to local mobile number which could be 9.1234567890
When India IP phone hits the US CME, it will send the call forward information to India CME which is 9.1234567890, India CME won;t able to complete this call because it is not its local number rather international.

To avoid this call forward looping, you'd need to disable H450.3 service in the forwarding CME.
It is activated by default on a CME with 3.1 or later versions, this service loops the call. The idea of this service is to minimize the resources being used at remote CME, choice of codecs for the new call leg as well as minimizing the WAN bandwidth. Here is what I got on my asn1 debugs on India CME-

value H4501SupplementaryService ::=
    {
      networkFacilityExtension
      {
        sourceEntity endpoint : NULL
        destinationEntity endpoint : NULL
      }
      interpretationApdu discardAnyUnrecognizedInvokePdu : NULL
      serviceApdu rosApdus :
      {
        invoke :
        {
          invokeId 5480
          opcode local : 19
          argument {"4824010180CB38000000010180CB530001018044..."}
        }
      }
    }

155673: May  9 15:45:11 SING: H450 INCOMING PDU ::=
  {
      reroutingReason 1
      originalReroutingReason 1
      calledAddress
      {
        destinationAddress
        {
          dialedDigits : "9805"
        }
      }
      diversionCounter 1
      h225InfoElement {}
      lastReroutingNr
      {
        destinationAddress
        {
          dialedDigits : "9820"
        }
      }
      subscriptionOption 0
      callingNumber
      {
        destinationAddress
        {
          dialedDigits : "1134"
        }
      }
      originalCalledNr
      {
        destinationAddress
        {
          dialedDigits : "9820"
        }
      }
    }

1134 dialed 9820 which was CFA to 9805 another local extension.

In order to disable h450.3 service, do the following. You'd need to disable it on CME B, in this case US CME-
Config t
Voice service voip
no supplementary-service h450.3


Good link for further information.

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