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'SIP Err: decoding failed' in call trace


A Dialogic® Integrated Media Gateway Call Trace may contain the message 'SIP Err: SIP message decoding failed':
03:59:53.290 SIP (W)   SIP Err: SIP message decoding failed, status= 1 at /ngcs
                       p/src/comps/sigSIP/src/tcb/src/tcb_mpre_tpf.c, 194
03:59:53.290 CALL(SIP) (00:00000:00)
                        ---> [, 33855]
03:59:53.290 SIP (W)   SIP Err: tcb_mpre_tpf_msg() failed at /ngcsp/src/comps/s
                       igSIP/src/tcb/src/tcb_mpre.c, 117
03:59:53.290 SIP (W)   SIP Err: Stale SIP msg handle: 3847 at /ngcsp/src/comps/
                       sigSIP/src/tcb/src/tcb_mpre.c, 130
03:59:53.290 SIP (W)   SIP Err: TCB message pre-processing failed at /ngcsp/src
                       /comps/sigSIP/src/src/sip_mpre.c, 200
Reason for the issue

The message indicates that the IMG SIP stack received data on its SIP port that it was unable to decode into a valid SIP message.  The particular line references to the C code are not enough to determine specifically what is wrong with the message.  
In order to determine what is wrong with the SIP message that the stack is unable to process, an Ethernet trace of the SIP traffic must be obtained while the messages are occurring.  Make a note, in the call trace, of the IP address that immediate follows the first error.  In this example:
 ---> [, 33855]

In this case, the arrow indicates the invalid message was received from IP address, and port 33855.  Using Wireshark to view the Ethernet trace that corresponds with the call trace, create a display filter that shows only packets received from the relevant source IP address and port:
(ip.src == && (udp.srcport == 33855)
After applying the display filter, all SIP messages from the offending endpoint will be displayed. 
Now, sort the packets by the Info column by clicking in the column name "Info."   This will make it easier to find the message that cannot be decoded.  There should only be "Request" and "Status" messages in the Info column. 
For any invalid message, the Info column will display "Source port" in this case 33855.
Once any offending packets are found, make a note of the packet number, in the first column and forward this information along with the trace, to the party responsible for that endpoint.

The only workaround, other than correcting the originating gateway, is to remove that gateway from the External Gateways list in the IMG configuration.
Product List

Dialogic® IMG 1004 Integrated Media Gateway
Dialogic® IMG 1010 Integrated Media Gateway
Dialogic® IMG 2020 Integrated Media Gateway (IMG 2020), formerly referred to as Dialogic® BorderNet™ 2020 Session Border Controller

Related Documentation


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First published: 06-Jan-2011
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