Overlap Receiving Issues

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Fri, 10/04/2013 - 03:39
Jun 29th, 2012

In some countries the Telco would send the digits in overlap and not as en-block.

En-bloc dialling expects all the information (esp the called party number) in one set up message.

In  overlap receiving the information is not received in one message.  Additional information elements are required for the call to be routed  properly.

The overlap receiving can be seen in the debug q931:

The  first set up message does not have the complete digits for the called  party number. Additional information elements follow thereafter for the  called digits:

The number dialled in this case is 9586874

060298: May 30 08:36:51.269: ISDN Se0/0/0:15 Q931: RX <- SETUP pd = 8  callref = 0x72BC

        Bearer Capability i = 0x8090A3

                Standard = CCITT

                Transfer Capability = Speech

                Transfer Mode = Circuit

                Transfer Rate = 64 kbit/s

        Channel ID i = 0xA98391

                Exclusive, Channel 17

        Calling Party Number i = 0x2181, '6224143323'

                Plan:ISDN, Type:National

        Called Party Number i = 0xC1, '95868'

                Plan:ISDN, Type:Subscriber(local)

        High Layer Compat i = 0x9181

060299:  May 30 08:36:51.269: ISDN Se0/0/0:15 Q931: Received SETUP  callref =  0xF2BC callID = 0x12BE switch = primary-net5 interface = User

060300: May 30 08:36:51.269: ISDN Se0/0/0:15 Q931: TX -> SETUP_ACK pd = 8  callref = 0xF2BC

        Channel ID i = 0xA98391

                Exclusive, Channel 17

Digit "7" being sent by the Telco as Additional Information Element:

060301: May 30 08:36:51.457: ISDN Se0/0/0:15 Q931: RX <- INFORMATION pd = 8  callref = 0x72BC

        Called Party Number i = 0xC1, '7'

                Plan:ISDN, Type:Subscriber(local)

Digit "4" being sent by the Telco as Additional Information Element:

060302: May 30 08:36:51.725: ISDN Se0/0/0:15 Q931: RX <- INFORMATION pd = 8  callref = 0x72BC

        Called Party Number i = 0xC1, '4'

                Plan:ISDN, Type:Subscriber(local)

In case the numbers are received as overlap, the following changes are advised on the router:

Avoid using the translations on the voice-ports. Use them on the incoming dial-peers rather.

interface serial 0/0/0:15

  isdn overlap-receiving t302 <time in milliseconds>

Incoming Dial Peer:

  dial-peer voice 1 pots

    incoming called number .T

The important thing to note is that direct inward-dial should not be configured in the incoming dial-peer

Outgoing dial-peer

  dial-peer voice 2 voip

   destination-pattern .T              <<<< the destination pattern in the outgoing dial-peer should terminate with .T

Another thing to note is the sending complete message.

060319: May 30 08:37:18.897: ISDN Se0/0/0:15 Q931: RX <- INFORMATION pd = 8  callref = 0x72BD

       Sending Complete


Incase  the information element has the sending complete message the wait timer  t302 would stop and the next step of matching the outgoing dial-peer  would proceed:

Links for reference:

Understanding Inbound and Outbound Dial Peers Matching on IOS Platforms:

http://www.cisco.com/en/US/tech/tk652/tk90/technologies_tech_note09186a008010fed1.shtml#topic5

Dial Planning:

http://www.cisco.com/en/US/docs/ios/12_3/vvf_c/dial_peer/dp_plan.html

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