Sorry, but I'm too lazy to compare those two messages byte by byte to
see if they are identical other than the version number.
I don't understand the point of your question. Are you looking for an
excuse to increment the version number without checking if the SDP has
changed?
There is a fine line here between what is required behavior, what is
good practice, what is considerate, ...
It really is a savings for the recipient of the SDP if he can avoid
parsing it. And generally it should be easier for the sender to "know"
that the SDP is unchanged and so indicate that when sending it. It is a
bit harder for the recipient to determine that. OTOH, as an implementor
I'm not very trusting and so am inclined to not trust that it is
unchanged without checking. Even so there are ways to take advantage of
that indication without trusting it. (If the version # is the same as
prior then do a string comparison of the two SDPs to verify. If the
version #s are different, then simply start parsing the SDP without
bothering with the comparison.)
And we shouldn't second guess what optimizations a peer may or may not
want to do.
I guess the worst case is a situation where you would normally generate
the SDP from scratch for every message and so not have an easy way to
tell if it has changed. Then it becomes a question of whether you do the
extra work to determine changed or not, or force extra work on the
recipient. I think you should do it.
The session timer connection is, IMO, a red herring. That draft is
poorly written, in that it seems to imply that an invite for session
timer is mutually exclusive with one for offer/answer. The two processes
share messages and can coexist or not.
Thanks,
Paul
On 1/22/20 6:50 AM, Sundbaum Per-Johan (Telenor Sverige AB) wrote:
Sorry for the no good picture !
SDP in 200OK for initial INVITE from PBX
SDP PDU
v=0
o=- 195986 1 IN IP4 10.81.253.92
s=RFC3264OfferAnswerExchange
c=IN IP4 10.81.253.92
b=CT:10000000
t=0 0
m=audio 23812 RTP/AVP 8 110
c=IN IP4 10.81.253.92
a=rtpmap:8 PCMA/8000
a=rtpmap:110 telephone-event/8000
a=fmtp:110 0-15
a=sendrecv
a=ptime:20
SDP in re-INVITE from PBX
SDP PDU
v=0
o=- 195986 2 IN IP4 10.81.253.92
s=RFC3264OfferAnswerExchange
c=IN IP4 10.81.253.92
b=CT:10000000
t=0 0
m=audio 23812 RTP/AVP 8 110
c=IN IP4 10.81.253.92
a=rtpmap:8 PCMA/8000
a=rtpmap:110 telephone-event/8000
a=fmtp:110 0-15
a=sendrecv
a=ptime:20
BR/pj
From: Rohit Jain <jainrohit...@gmail.com>
Sent: den 22 januari 2020 12:36
To: Sundbaum Per-Johan (Telenor Sverige AB) <per-johan.sundb...@telenor.se>
Cc: sip-implementors@lists.cs.columbia.edu
Subject: Re: [Sip-implementors] SDP version
Hi,
SIP entities (client/server) checks SDP version to determine whether there is
any change in SDP from previously received SDP. If the version is changed then
they go on to parse the entire SDP to determine the change.
Based on that SIP entity can initiate media processing(more relevant in case of
servers) or just relay the message without any media level processing. If just
the version number is incremented but there is no actual change in SDP, then it
will trigger unnecessary processing on the receiver, so it should be avoided.
Also can you specify what could be the requirement ("but is that true also for UA
without support for timer") in which it is required to increment the SDP version
number without any actual change in SDP.
PS: Not able to get the attached picture.
Regards,
Rohit J
On Wed, Jan 22, 2020 at 4:31 PM Sundbaum Per-Johan (Telenor Sverige AB)
<per-johan.sundb...@telenor.se<mailto:per-johan.sundb...@telenor.se>> wrote:
Hi !
What do you think about incrementing the version in SDP o-line, but not
changing anything else in SDP,
should such a behavior be accepted or should it be rejected ?
RFC 4028 states that such behavior at least should be avoided, but is that true
also for UA without support for timer ?
" RFC 4028 - Session Timer
In that case, the offer MUST indicate
that it has not changed. In the case of SDP, this is accomplished by
including the same value for the origin field as did previous SDP
messages to its peer. The same is true for an answer exchanged as a
result of a session refresh request; if it has not changed, that MUST
be indicated. "
An example from reality in picture below, should it be accepted ?
I think it should be accepted.
[cid:image001.png@01D5D11B.59A78290]
BR/pj
Sensitivity: Internal
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--
Regards,
Rohit Jain
Sensitivity: Internal
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