Subject: [Megaco] how codec negotiation is triggered by MGC?

From: Richard Sun <[email-masked]>
Date: Thu, 16 Dec 2004 09:08:14 -0500

Hi, Can anyone pelase clarify the standard
for MGC to trigger a codec negotiation in MG
(i.e, MG should provide a list of codecs
it supports)?

One way I can think of is an empty "Local{}"
without SDP, such as:
Transaction = 299012 {
  Context = $ {
    Add = aaln/1 {
      Media { Stream = 1 {
        LocalControl {Mode = SendReceive}
    }}},
    Add = $ {
      Media {Stream = 1 {
        LocalControl {Mode=ReceiveOnly},
        Local {}
}}}}}

The question is: is this legal? Should MG reject
the message with some kind of error such as "SDP missing",
or MG is suppose to fill up the SDP section in response?
What if the "Local{}" does not present at all?

The other way is something like this:
Transaction = 299012 {
  Context = $ {
    Add = aaln/1 {
      Media { Stream = 1 {
        LocalControl {Mode = SendReceive}
    }}},
    Add = $ {
      Media {Stream = 1 {
        LocalControl {Mode=ReceiveOnly},
        Local {
v=0
o=$ $ $ IN IP4 $
s=$
c=IN IP4 $
t=$ $
m=audio $ RTP/AVP -
a=ptime:20
}}}}}}
With "-" in "m=audio $ RTP/AVP -", should MG
fill up the list of codecs?
Or should it be something like
"m=audio $ RTP/AVP $"?

Thanks for any information.
-Richard

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