On Wed, Jun 15, 2011 at 5:11 PM, Michael Collins <
msc@freeswitch.org> wrote:
> Ah, quite right. I'd file this in Jira. Hopefully it's not buried deep in
> the Sofia stack...
> -MC
>
> On Wed, Jun 15, 2011 at 2:58 PM, Kristian Kielhofner <
kris@kriskinc.com>
> wrote:
>>
>> Michael,
>>
>> This isn't an SDP offer/answer issue with FreeSWITCH. Even if there
>> were underlying offer/answer issues between the endpoints FreeSWITCH
>> is in bypass_media mode and it shouldn't care about the SDP because by
>> definition (bypass_media) the SDP is "pass through" between the two
>> remote endpoints.
>>
>> The specific issue lies in the 183 w/ SDP at line 207. It has
>> rfc2833 payload type 110. When FreeSWITCH forwards this to the other
>> end (line 276) the SDP is untouched (expected with bypass_media)
>> EXCEPT the rfc2833 payload type has been changed to 101 (unexpected
>> with bypass_media). It does this again with the 200 OK. All other
>> SDP params are passed through - media address, port, codec, goofy
>> session name, and even the SER rtpproxy attributes. I'll admit the
>> remote end/proxy is doing some strange stuff - 100, 101, 183, then
>> 180, etc but this does look like a strange bypass_media bug in
>> FreeSWITCH. The RFC2833 payload type should be forwarded between the
>> two remote endpoints without being modified by FreeSWITCH - just like
>> all of the other SDP parameters (or any part of the SIP body, for that
>> matter).
>>
>> On Wed, Jun 15, 2011 at 5:09 PM, Michael Collins <
msc@freeswitch.org>
>> wrote:
>> > QQ,
>> > I don't see that FreeSWITCH is doing anything incorrect here. According
>> > to
>> > RFC3264, the offerer (FreeSWITCH) sends an SDP and in the case of RTP,
>> > the
>> > answerer (GRSIP Gateway) must use the payload type offered, even if the
>> > answerer uses a different payload type when it sends a telephone-event.
>> >
http://tools.ietf.org/html/rfc3264#section-6.1
>> > Specifically near the end:
>> > "In the case of RTP, it MUST use the payload type numbers
>> >
>> > from the offer, even if they differ from those in the answer."
>> >
>> > Technically, FreeSWITCH isn't "changing" anything anyway. The originator
>> > of
>> > the call (Vox Callcontrol) is the one who chose PT 101 in the INVITE
>> > that it
>> > sent to FreeSWITCH. FS is just passing that along without modifying it.
>> > I think you need to contact the people running the gateway and make sure
>> > that they understand that they are not following RFC3264 if they're
>> > rejecting telephone-events in PT 101 simply because they prefer to send
>> > in
>> > PT 110. Also, if your Vox Callcontrol client has any configuration
>> > options
>> > then maybe you can tell it to use PT 110 for RFC2833 DTMFs. It is a bit
>> > of a
>> > workaround but this is SIP, so no one is expecting perfection. :)
>> > -MC
>>
>> --
>> Kristian Kielhofner
>>
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