Hi Attila,
"Can you show me an example of how you would do this?"
IMO to completely describe a codec one should provide the max packet time
the codec can accept on receiving and also the desired packet time for
sending / receiving. Ideally and if it was up to me to define it, I would
have combined all this information in the rtpmap attribute as follows:
a=rtpmap:<payload type> <encoding name>/<clock rate>[/<encoding parameters>]
<max recv ptime> <preferred send recv ptime>
For example my g.711 implementation by firmware limitation cannot receive
more than 30ms packets and based on bandwidth restrictions and voice quality
concerns I would like to send/receive at 10ms. I would indicate this as
follows:
a=rtpmap:0 PCMU/8000 30 10
But his is asking for changing the rtpmap attribute definition and as such
is not likely to be taken easy.
Instead, I think it is more likely to come to an agreement on a "better" use
of the already "loosely" defined ptime and maxptime attributes to describe
each individual codec as in the following example where each ptime and
maxptime describes the rtpmap above it:
m=audio 5004 RTP/AVP 0 4 18 101
a=rtpmap:0 PCMU/8000
a=ptime:10
a=maxptime:30
a=rtpmap:4 G723/8000
a=ptime:30
a=maxptime:60
a=rtpmap:18 G729/8000
a=ptime:20
a=maxptime:80
a=rtpmap:101 telephone-event/8000
With this approach there is no need to specify ptime and maxptime for
rfc2283.
Do you think something like that could be defined and agreed upon?
Regards,
Danail
-----Original Message-----
From: Attila Sipos [mailto:[EMAIL PROTECTED]
Sent: Tuesday, November 02, 2004 1:53 PM
To: Danail Kirov; Danail Kirov; Linda Xiao; [EMAIL PROTECTED]
Subject: RE: [Sip-implementors] Does RFC3264 allow different ptime for
different audio codecs?
Hi Danail,
>>2. How is the rfc2283 packet time presented if rfc2283 is listed in the
>>"m=" line?
As you know, the RFC2833 packet interval should be the same
as that for the selected RTP. So, the RFC2833 packet time
can't be fixed - and so a '-' is used.
m=audio 5004 RTP/AVP 0 4 97 18
a=rtpmap:0 PCMU/8000
a=rtpmap:97 telephone-event/8000
a=mptime:10 30 - 20
>>3. The most important question. Can somebody definitely say that based on
>>RFC3264 and RFC2327 one can not use more than one "a=ptime" line?
I would say that it doesn't explicitly say you can't use more than
one ptime line. It also does not explicitly say that multiple
lines of ptime should be used to indicate separate packet times
for the different codecs.
>>The
>>following is a question from Christer Holmberg which was left unanswered
in
>>your previous thread and is exactly my question as well: "Which "rules"
are
>>you refering to?
When I said "the rules", I meant the rules in the SDP RFC 2327.
The problem is that the ptime attribute, in my interpretation,
is not related to a specific profile but to a specific media
description. So this is a problem if you have multiple profiles
with different packet times.
>>RFC2327 does say ptime is a media attribute, but I can't
>>find anywhere said that you can't specify separate values for specific
>>codecs (using it together with rtpmap)."
Can you show me an example of how you would do this?
Regards,
Attila
-----Original Message-----
From: Danail Kirov [mailto:[EMAIL PROTECTED]
Sent: Tue 02/11/2004 19:36
To: Attila Sipos; Danail Kirov; Linda Xiao;
[EMAIL PROTECTED]
Cc:
Subject: RE: [Sip-implementors] Does RFC3264 allow different ptime
for different audio codecs?
Attila,
I've researched the archives and found you had similar discussions
last
year, but it appears there are questions still unanswered. Maybe you
guys
resolved them in some other form.
1. Where is the use of mptime defined? I looked at the PacketCable
docs
referenced at some threads and couldn't find it there.
2. How is the rfc2283 packet time presented if rfc2283 is listed in
the "m="
line?
3. The most important question. Can somebody definitely say that
based on
RFC3264 and RFC2327 one can not use more than one "a=ptime" line?
The
following is a question from Christer Holmberg which was left
unanswered in
your previous thread and is exactly my question as well: "Which
"rules" are
you refering to? RFC2327 does say ptime is a media attribute, but I
can't
find anywhere said that you can't specify separate values for
specific
codecs (using it together with rtpmap)."
I am surprised the SIP community would leave this unaddressed for
such a
long time?
Regards,
Danail Kirov
-----Original Message-----
From: Attila Sipos [mailto:[EMAIL PROTECTED]
Sent: Tuesday, November 02, 2004 1:05 AM
To: Danail Kirov; Linda Xiao; [EMAIL PROTECTED]
Subject: RE: [Sip-implementors] Does RFC3264 allow different ptime
for
different audio codecs?
This is still an officially unaddressed problem (and I really
don't understand why).
We (and some others) support the mptime or (x-mptime)
attribute.
So your list would get compressed to:
m=audio 5004 RTP/AVP 0 4 18
a=rtpmap:0 PCMU/8000
a=mptime:10 30 20
Some use x-mptime instead of mptime:
a=x-mptime:10 30 20
We allow for both.
Regards,
Attila
Software Engineer
http://www.vegastream.com/
-----Original Message-----
From: [EMAIL PROTECTED] on behalf of
Danail
Kirov
Sent: Tue 02/11/2004 00:51
To: 'Linda Xiao'; [EMAIL PROTECTED]
Cc:
Subject: RE: [Sip-implementors] Does RFC3264 allow different
ptime
for different audio codecs?
The problem with this approach is that I can not specify
what is my
codec
preference 0, 4 or 18 - i.e all of them are equal.
Also with this approach the "answerer" may choose to accept
all "m="
streams
and to start sending audio data on all 3 of them...while I
really
want a
single audio stream.
-----Original Message-----
From: Linda Xiao [mailto:[EMAIL PROTECTED]
Sent: Monday, November 01, 2004 4:30 PM
To: 'Danail Kirov'; [EMAIL PROTECTED]
Subject: RE: [Sip-implementors] Does RFC3264 allow
different
ptime
for dif ferent audio codecs?
I think you can (or should) use multi-line of "m=".
m=audio 5004 RTP/AVP 0
a=rtpmap:0 PCMU/8000
a=ptime:10
m=audio 5004 RTP/AVP 4
a=rtpmap:4 G723/8000
a=ptime:30
m=audio 5004 RTP/AVP 18
a=rtpmap:18 G729/8000
a=ptime:20
Regards/Linda
-----Original Message-----
From: Danail Kirov [mailto:[EMAIL PROTECTED]
Sent: Monday, November 01, 2004 4:14 PM
To: [EMAIL PROTECTED]
Subject: [Sip-implementors] Does RFC3264 allow different
ptime for
different
audio codecs?
Hi All,
Is it allowed to add
a=ptime:xx
for every codec listed in a single m= line?
For example:
m=audio 5004 RTP/AVP 0 4 18
a=rtpmap:0 PCMU/8000
a=ptime:10
a=rtpmap:4 G723/8000
a=ptime:30
a=rtpmap:18 G729/8000
a=ptime:20
All the samples I've seen so far imply there is only one
ptime per
m= line,
but this does not describe the "real world" where one would
want to
use
different audio codecs with different packet times and
different
codecs
operate on different [ms] frames.
G.711 - 1ms
G.729 - 10ms
G.723 - 30ms
i.e - specifiying 10ms does not make any sense for G.723,
but does
for
G.729 and G.711.
Regards,
Danail Kirov
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