G729, G729B and RFC3555 Problem

tpaquette · ‎04-22-2007

Sorry, this was meant to be posted in "IP Telephony"

In July of 2003, rfc3555 was released.

In it was defined the various parameters and semantics for SIP SDP audio codec negotiation

Of note was the declaration that, when negotiating a G729 (not G729B) RTP session (using SIP) an "annexb=no" SDP parameter needs to be defined otherwise the audio session will default to G729 annexB

The issue is that there are many entities out there that still use the old semantics, which forces me to use G729B when terminating a call on a RFC3555 compliant cisco gateway

This is the SDP payload of a SIP message generated by a PRE-RFC3555 endpoint that wants to use G729 (not G729B)

----

v=0

o=CiscoSystemsSIP-GW-UserAgent 4001 7365 IN IP4 OBSCURED

s=SIP Call

c=IN IP4 OBSCURED

t=0 0

m=audio 17268 RTP/AVP 18

c=IN IP4 OBSCURED

a=rtpmap:18 G729/8000

----

When this message is sent an RFC3555 compliant endpoint it will force the use of G729B (as the "annexb=no" parameter isn't defined)

According to RFC3555 this would be the proper format for the SDP payload:

----

v=0

o=CiscoSystemsSIP-GW-UserAgent 4001 7365 IN IP4 OBSCURED

s=SIP Call

c=IN IP4 OBSCURED

t=0 0

m=audio 17268 RTP/AVP 18

c=IN IP4 OBSCURED

a=rtpmap:18 G729/8000

a=fmtp:18 annexb=no

----

Pre 12.3 IOSs used the old semantics, however there are a few features in 12.3 (which implements RFC3555) that i need so it would be difficult for me to downgrade.

Is there a way to change the behavior of the AS5300 to use the old semantics instead of those defined in RFC3555?

Otherwise i am forced to used G729B, this is a serious limitation for us.

I'm currently using, c5300-is-mz.123-22.bin

Tavis Paquette

Report Inappropriate Content · ‎04-27-2007

In IOS SIP gateways complaint to RFC 3555, you need to specify the exact G.729 type of codec in the configuration. Another solution is to downgrade the IOS to a version which is not RFC 3555 complaint

http://www.cisco.com/en/US/products/sw/iosswrel/ps1839/products_feature_guide09186a00800b5d75.html

http://www.cisco.com/en/US/products/hw/routers/ps259/products_tech_note09186a00800a74d7.shtml

tpaquette · ‎04-27-2007

The issue is that when I specify, in the codec class, that i was to use only g729r8 and my SIP switch that it not compliant tries to establish a g729 session the cisco Gateway thinks (in line with the semantics of RFC3555) that the switch wants to establish a g729br8 session and rejects the call

We can't downgrade to 12.2 due to our use of some features of 12.3

It seems strange that there wouldn't be some way to work around this issue as its very common in the industry for endpoints to not support RFC3555 which instantly creates this issue when trying to use G729

richardbuxton · ‎02-15-2008

Hello,

I also have this issue and am not able to downgrade IOS.

Does anyone have any alternative solutions to this issue? Can RFC3555 be disabled in IOS?

Any help would be appreciated

Regards

Richard

Cesar Alonso · ‎12-11-2014

Hi Richard,

You can use this command "g729-annexb override".

Regards,

Cesar Alonso