[Sip-implementors] Is it valid a=rtpmap:96 telephone-event/8000 ?

[Iñaki Baz Castillo]

Hi, is it valid the following (fragment of an) SDP?:

m=audio 5970 RTP/AVP 18 0 4 8 96
a=rtpmap:18 G729/8000
a=rtpmap:0 PCMU/8000
a=rtpmap:4 G723/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:96 telephone-event/8000


I know that RFC 2833 or 4733/4734 do not mandate a specific payload
value for DTMF, but AFAIK values below 100 are reserved, am I wrong?
This is, values below 100 are supposed to indicate standarized values
(as some codecs). Please correct me if I'm wrong.

Thanks a lot.

[Iñaki Baz Castillo]

Post by Iñaki Baz Castillo
I know that RFC 2833 or 4733/4734 do not mandate a specific payload
value for DTMF, but AFAIK values below 100 are reserved, am I wrong?
This is, values below 100 are supposed to indicate standarized values
(as some codecs). Please correct me if I'm wrong.

I'm wrong, the first payload dynamic value is 96 as Valdelrmar Pamesi
pointed out some time ago in this maillist replying to me:


---------------------------------------

rfc3551 defines codec names which can be used in SDP while IANA maps
codecs names to a number known as payload number


Registry:
PT encoding name audio/video (A/V) clock rate (Hz) channels
(audio) Reference
-------- -------------- ----------------- ---------------
---------------- ---------
0 PCMU A 8000 1
[RFC3551]
1 Reserved
2 Reserved
3 GSM A 8000 1
[RFC3551]
4 G723 A 8000 1
[Kumar]
5 DVI4 A 8000 1
[RFC3551]
6 DVI4 A 16000 1
[RFC3551]
7 LPC A 8000 1
[RFC3551]
8 PCMA A 8000 1
[RFC3551]
9 G722 A 8000 1
[RFC3551]
10 L16 A 44100 2
[RFC3551]
11 L16 A 44100 1
[RFC3551]
12 QCELP A 8000 1
13 CN A 8000 1
[RFC3389]
14 MPA A 90000
[RFC3551][RFC2250]
15 G728 A 8000 1
[RFC3551]
16 DVI4 A 11025 1
[DiPol]
17 DVI4 A 22050 1
[DiPol]
18 G729 A 8000 1
19 Reserved A
20 Unassigned A
21 Unassigned A
22 Unassigned A
23 Unassigned A
24 Unassigned V
25 CelB V 90000
[RFC2029]
26 JPEG V 90000
[RFC2435]
27 Unassigned V
28 nv V 90000
[RFC3551]
29 Unassigned V
30 Unassigned V
31 H261 V 90000
[RFC4587]
32 MPV V 90000
[RFC2250]
33 MP2T AV 90000
[RFC2250]
34 H263 V 90000
[Zhu]
35-71 Unassigned ?
72-76 Reserved for RTCP conflict avoidance
[RFC3551]
77-95 Unassigned ?
96-127 dynamic ?
[RFC3551]

[Worley, Dale R (Dale)]

________________________________________
From: sip-implementors-bounces at lists.cs.columbia.edu [sip-implementors-bounces at lists.cs.columbia.edu] On Behalf Of I?aki Baz Castillo [ibc at aliax.net]

Hi, is it valid the following (fragment of an) SDP?:

m=audio 5970 RTP/AVP 18 0 4 8 96
a=rtpmap:18 G729/8000
a=rtpmap:0 PCMU/8000
a=rtpmap:4 G723/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:96 telephone-event/8000

I know that RFC 2833 or 4733/4734 do not mandate a specific payload
value for DTMF, but AFAIK values below 100 are reserved, am I wrong?
This is, values below 100 are supposed to indicate standarized values
(as some codecs). Please correct me if I'm wrong.
_______________________________________________

It is valid to assign a codec to payload 96. IIRC, it is *valid* but not recommended
to assign a codec to any payload number, including those that have static assignments.

But historically, some Cisco gear only used payload 101 for receiving telephone-event,
even if the SDP specified a different payload number. So it has become conventional
to always use 101 for telephone-event.

Dale

[Iñaki Baz Castillo]

Post by Worley, Dale R (Dale)
But historically, some Cisco gear only used payload 101 for receiving telephone-event,
even if the SDP specified a different payload number. ?So it has become conventional
to always use 101 for telephone-event.

This could be the exact problem I'm issuing with some client.

Thanks.