CM: CM does not answer with 200 OK upon sending 180 ringing

Doc ID    SOLN260082
Version:    5.0
Status:    Published
Published date:    30 Dec 2020
Created Date:    27 Nov 2014
Author:   
Luca Bonaita
 

Details

CM doesn't send back 200 OK after answering the call.

CM R02.0.823.0-19721
 

Problem Clarification

First INVITE comes in form SBC to CM with the option Supported: 100rel .
CM responds with 180 Ringing and Require: 100rel.

If 180 Ringing has Require: 100rel, other side SP(Service Provider) should acknowledge the provisional response with PRACK and 200OK.
In this scenario, SP should acknowledge the 180 RINGING with PRACK: if not CM keeps on sending 180 message until call is cleared from SP side because no 200 OK received(timeout).

We should see Sipera SBC propagating the "180 Ringing with 100rel" from CM to the PSTN.
If SP is failing to respond with a PRACK to the 180 ringing with 100rel, that prevents CM from sending 200 OK
back to SIP set. Furthermore, SIP set is unable to answer call due to CM not returning a 200 OK to the original call.

10.237.0.65 = SBC internal
192.168.69.249 = SBC external that is NATed to public IP address 213.141.15.166
10.237.0.52 = SM100
10.237.0.51 = SM
10.237.0.2 = CM
213.141.11.51= SBCE service provider
 

       SBC/10.237.0.65          SM100        CM/10.237.0.2           MG/10.237.0.31

13:30:26.785 |--INVITE-->|                     |             | (538) T:210339912 F:969510415 U:210339912

13:30:26.786 |<--Trying-- |                     |             | (538) 100 Trying

13:30:26.814 |                              |--INVITE-->|                    | (538) T:210339912 F:969510415 U:210339912 P:terminating

13:30:26.815 |             |<--Trying-- |                    | (538) 100 Trying

13:30:26.818 |                              |<--Ringing-|                    | (538) 180 Ringing

13:30:26.818 |<============G729============>           | (538) RTP 10.237.0.65:36152 <-G729-> 10.237.0.31:10210

13:30:26.823 |<--Ringing-|                     |             | (538) 180 Ringing

13:30:27.322 |                              |<--Ringing-|                    | (538) 180 Ringing

13:30:27.326 |<--Ringing-|                     |             | (538) 180 Ringing

 

First INVITE comes in form SBC to CM with the option Supported: 100rel .

CM responds with 180 Ringing and Require: 100rel.

 

If 180 Ringing has Require: 100rel, other side SP(Service Provider) should acknowledge the provisional response with PRACK and 200OK.

In your scenario SP should acknowledge the 180 RINGING with PRACK: if not CM keeps on sending 180 message until call is cleared from SP side because no 200 OK received(timeout).

SBC/10.237.0.65 SM100 CM/10.237.0.2 MG/10.237.0.31
13:30:26.785 |--INVITE-->| | | (538) T:210339912 F:969510415 U:210339912
13:30:26.786 |<--Trying-- | | | (538) 100 Trying
13:30:26.814 | |--INVITE-->| | (538) T:210339912 F:969510415 U:210339912 P:terminating
13:30:26.815 | |<--Trying-- | | (538) 100 Trying
13:30:26.818 | |<--Ringing-| | (538) 180 Ringing
13:30:26.818 |<============G729============> | (538) RTP 10.237.0.65:36152 <-G729-> 10.237.0.31:10210
13:30:26.823 |<--Ringing-| | | (538) 180 Ringing
13:30:27.322 | |<--Ringing-| | (538) 180 Ringing
13:30:27.326 |<--Ringing-| | | (538) 180 Ringing

 

First INVITE comes in form SBC to CM with the option Supported: 100rel .
CM responds with 180 Ringing and Require: 100rel.

If 180 Ringing has Require: 100rel, other side SP(Service Provider) should acknowledge the provisional response with PRACK and 200OK.
In your scenario SP should acknowledge the 180 RINGING with PRACK: if not CM keeps on sending 180 message until call is cleared from SP side because no 200 OK received(timeout).

Cause

According to the trace,  SBC is responding to CM 180 ringing with PRACK. But PRACK is blocked at 192.168.69.249 IP with 500 error.
192.168.69.249 is SBC external that is NATed to public IP address 213.141.15.166.
So the problem sits on SBC configuration. CM and SM are behaving correctly

Solution


  Service Provider needs to fix SBC to provide the PRACK to the 180 Ringing.

Per the RFC3261, if there is a 100rel in the 180 ringing message, a PRACK is required as response.

Additional Relevant Phrases

cannot connect to Telstra with Avaya SBC 482 Loop Detected

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