[Asterisk-Users] Fax over SIP Problems (sorry for this topic ...)

[Kai Militzer]

Hello everyone!

I tried to send a fax over SIP with an Asterisk Server in the middle (no
Digium Cards, etc. installed, everything is SIP only, the PSTN-Gateway
is external). Whenever I start sending a Fax to a PSTN destination, the
Call gets answered and asterisk tries to build a native bridging:

-- Attempting native bridge of SIP/sip.westend.com-082fd1b8 and
SIP/xxx-3ef8

Then the following messages start to appear (about 100 of them)

Nov 23 16:27:25 NOTICE[1061908]: rtp.c:489 ast_rtp_read: Unknown RTP
codec 127 received

After that asterisk gets totaly confused:

Nov 23 16:27:33 WARNING[1061908]: rtp.c:428 ast_rtp_read: RTP Read too
short
Nov 23 16:27:33 WARNING[1061908]: rtp.c:428 ast_rtp_read: RTP Read too
short
Nov 23 16:27:33 WARNING[1061908]: rtp.c:428 ast_rtp_read: RTP Read too
short
Nov 23 16:27:33 WARNING[1061908]: rtp.c:428 ast_rtp_read: RTP Read too
short
Nov 23 16:27:35 NOTICE[1061908]: rtp.c:489 ast_rtp_read: Unknown RTP
codec 1 received
Nov 23 16:27:35 WARNING[1061908]: codec_gsm.c:135 gsmtolin_framein:
Huh?  A GSM frame that isn't a multiple of 33 or 65 bytes long from RTP
(15)?
Nov 23 16:27:35 NOTICE[1061908]: channel.c:1724 ast_set_read_format:
Unable to find a path from G723 to ALAW
Nov 23 16:27:35 NOTICE[1061908]: channel.c:1691 ast_set_write_format:
Unable to find a path from GSM to G723
Nov 23 16:27:35 WARNING[1061908]: codec_gsm.c:135 gsmtolin_framein:
Huh?  A GSM frame that isn't a multiple of 33 or 65 bytes long from RTP
(20)?
Nov 23 16:27:35 WARNING[1061908]: channel.c:2115
ast_channel_make_compatible: No path to translate from
SIP/sip.westend.com-082fd1b8(8) to SIP/xxx-3ef8(1)
Nov 23 16:27:35 WARNING[1061908]: channel.c:2633 ast_channel_bridge:
Can't make SIP/sip.westend.com-082fd1b8 and SIP/xxx-3ef8 compatible
Nov 23 16:27:35 WARNING[1061908]: res_features.c:358 ast_bridge_call:
Bridge failed on channels SIP/sip.westend.com-082fd1b8 and SIP/xxx-3ef8
  == Spawn extension (macro-enumcall, s, 211) exited non-zero on
'SIP/sip.westend.com-082fd1b8' in macro 'enumcall'
  == Spawn extension (xxx, 911879, 7) exited non-zero on
'SIP/sip.westend.com-082fd1b8'
    -- Executing NoOp("SIP/sip.westend.com-082fd1b8", "") in new stack
       > cdr_odbc: Query Successful!

Then the call gets hung up. I cannot explain why this happens. I would
have explanations for the fax-machines not able to synchronize or faxes
not being transmitted correctly, as the communication is SIP only, but
this seems a bit strange to me. I can't even tell, if my asterisk
produces these messages, or the other side (aka PSTN-Gateway).

If anyone can bring some light into this behavior I would be very
greatful.

Best regards

Kai

-- 
Kai Militzer                 WESTEND GmbH  |  Internet-Business-Provider
Technik                      CISCO Systems Partner - Authorized Reseller
                             Lütticher Straße 10      Tel 0241/701333-11
km at westend.com               D-52064 Aachen              Fax 0241/911879