[asterisk-users] T38 negotiation, the last step !

[Miguel Molina]

Xavier Cardil escribió:
> Hi, I've managed to get HYLAFAX---->T38MODEM----->
> ASTERISK---->CISCOAS5400 working, but when they are negotiating 
> asterisk drops a message telling "Unknown RTP codec 96 received from 
> gateway" Do somebody know how to fix it ? 
>
> Thank you !
>
>
>
> << [ TYPE: Control (4) SUBCLASS: Ringing (3) ] [SIP/GWCISCO5400O-600bfcc8]
> << [ TYPE: Control (4) SUBCLASS: Answer (4) ] [SIP/GWCISCO5400O-600bfcc8]
> << [ TYPE: Null Frame (5) SUBCLASS: N/A (0) ] [SIP/GWCISCO5400O-600bfcc8]
> << [ TYPE: Null Frame (5) SUBCLASS: N/A (0) ] [SIP/GWCISCO5400O-600bfcc8]
> << [ TYPE: Control (4) SUBCLASS: T38/Negotiation Requested (19) ] 
> [SIP/GWCISCO5400O-600bfcc8]
> << [ TYPE: Null Frame (5) SUBCLASS: N/A (0) ] [SIP/GWCISCO5400O-600bfcc8]
> [Jul 16 17:50:39] NOTICE[2736]: rtp.c:1739 ast_rtp_read: Unknown RTP 
> codec 96 received from '192.168.3.163'
> << [ TYPE: Null Frame (5) SUBCLASS: N/A (0) ] [SIP/GWCISCO5400O-600bfcc8]
> [Jul 16 17:50:40] NOTICE[2736]: rtp.c:1739 ast_rtp_read: Unknown RTP 
> codec 96 received from '192.168.3.163'
> << [ TYPE: Null Frame (5) SUBCLASS: N/A (0) ] [SIP/GWCISCO5400O-600bfcc8]
> [Jul 16 17:50:41] NOTICE[2736]: rtp.c:1739 ast_rtp_read: Unknown RTP 
> codec 96 received from '192.168.3.163'
> << [ TYPE: Null Frame (5) SUBCLASS: N/A (0) ] [SIP/GWCISCO5400O-600bfcc8]
> << [ TYPE: Null Frame (5) SUBCLASS: N/A (0) ] [SIP/GWCISCO5400O-600bfcc8]
> << [ TYPE: Null Frame (5) SUBCLASS: N/A (0) ] [SIP/GWCISCO5400O-600bfcc8]
It looks like the Cisco gateway is trying to negotiate or send some 
video codec or something which asterisk does not recognize. According to 
the spec (http://www.iana.org/assignments/rtp-parameters), The codecs 96 
to 127 are dynamic RTP payloads that are negotiated with another 
protocols to define them. If everything else on your fax session works 
fine, this message shouldn't be a problem. I think this is much like the 
X-lite 126 codec type message:

[Jul 16 11:35:57] NOTICE[10989]: rtp.c:1287 ast_rtp_read: Unknown RTP 
codec 126 received from '0.0.0.0'

And doesn't pose a problem anyway.

-- 
Ing. Miguel Molina
Grupo de Tecnología
Millenium Phone Center
PBX: (+57 1)6500800 ext. 1201
Fax: (+57 1)6500816
Móvil: (+57)3138873587