RE: Clarification on MG handling of Local & Remote Descriptors
Kevin Boyle <kboyle <at> nortel.com>
2005-07-06 14:51:34 GMT
There is no requirement that the Local and Remote descriptors align.
This would allow for some interesting things, like asymmetric codecs.
The reality, however, is that many implementations do not like
asymmetric connections and will not be able to do such a thing. This
being said, however, the MG may not choose to add things to SDP that are
not there. If the MGC has specified a particular codec (8 in your
example) the MG may not add more codecs. It is constrained by what is
in the description from the MGC.
If the MG can align the Local and Remote within the constraints that the
MGC has placed on the Local descriptor, that is certainly allowed and is
the prerogative of the MG.
From: megaco-bounces <at> ietf.org [mailto:megaco-bounces <at> ietf.org] On Behalf
Of Kamitses, Jerry
Sent: Tuesday, July 05, 2005 7:48 PM
To: megaco <at> ietf.org
Subject: [Megaco] Clarification on MG handling of Local & Remote
A question has arisen during interop testing regarding the extent to
which the content of Local and Remote Descriptors sent to an MG
termination by the MGC are intended to limit the content of any Local
Descriptor returned by that MG termination in a response message.
The question concerns whether the Local Descriptor in the MG
termination's response must always be a subset of the last Local
Descriptor sent to that termination or whether there are circumstances
where the MG termination is free to include additional information in
the response Local Descriptor.
For example, are there situations where the content of the Remote
descriptor must or may effect the content of the Local Descriptor the MG
In particular, if the last received Remote descriptor contains
information not present in the last received Local descriptor then is
the MG free to use any/all of the Remote Descriptor contents in addition
to the last received Local Descriptor when selecting the Local
Descriptor to return?
Specifically, what are the rules regarding SDP media parameters in the
If, for example, the Local and Remote descriptors sent to the MG are
o=- $ 0 IN IP4 $
c=IN IP4 $
m=audio $ RTP/AVP 8
o=- 0 0 in ip4 126.96.36.199
c=in ip4 188.8.131.52
m=audio 5000 rtp/avp 18 101
then can the MG choose to return the following Local Descriptor?
o=- 0 0 in ip4 184.108.40.206
c=in ip4 220.127.116.11
m=audio 6348 rtp/avp 18 101
Do dynamic payloads based on RFC 2833 handled require any special
treatment in this regard? For example, if the Remote Descriptor contains
a telephone-event rtpmap and the Local Descriptor does not, then can the
MG choose to include a telephone-event rtpmap in the Local Descriptor it
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