Megaco MediaDescriptor sending multiStream instead of oneStream

Peter-Henry Mander <>
Wed Oct 2 18:11:17 CEST 2002


Thanks Håkan. Yes, it was a bit confusing.

It did force me to deal with both oneStream and multiStream media 
descriptors where I initially had assumed only oneStream (Oops! :-)

Pete.

Hakan Mattsson wrote:
> On Tue, 1 Oct 2002, Peter-Henry Mander wrote:
> 
> Pete> I've got another query, and as you've been a great help already I'm 
> Pete> asking you directly. I'm sending out a AmmRequest with the following 
> Pete> format:
> Pete> 
> Pete> 	      #'AmmRequest'{
> Pete> 		      terminationID = [TermId],
> Pete> 		      descriptors = [
> Pete> 			      {	mediaDescriptor,
> Pete> 				      #'MediaDescriptor'{streams = {oneStream, StreamParms}}}]
> Pete> 	      };
> Pete> 
> Pete> Note the oneStream streams field. What I receive at the other end is:
> Pete> 
> Pete> {'MediaDescriptor',asn1_NOVALUE,
> Pete> 			 {multiStream,[{'StreamDescriptor',
> Pete> 					   1,
> Pete> 					   {'StreamParms',
> Pete> 					       {'LocalControlDescriptor',
> Pete> 						   asn1_NOVALUE,
> Pete> 						   asn1_NOVALUE,
> Pete> 						   asn1_NOVALUE, ...etc...
> Pete> 
> Pete> And the megaco message looks like this:
> Pete> 
> Pete> Transaction = 26 {
> Pete> 	      Context = $ {
> Pete> 		      Add = $ {
> Pete> 			      Media {
> Pete> 				      Stream = 1 {
> Pete> 					      LocalControl { ...etc...
> 
> Our encoder and decoder is not symmetric in this case.
> 
> Your message is encoded as:
> 
> 	Transaction = 26 {
> 		      Context = $ {
> 			      Add = $ {
> 				      Media {
> 					      LocalControl { ...etc...
> 
> but interpreted by the decoder as if it was:
> 
> 	Transaction = 26 {
> 		      Context = $ {
> 			      Add = $ {
> 				      Media {
> 					      Stream = 1 {
> 						      LocalControl { ...etc...
> 
> which is semantically the same thing.
> 
> Pete> I suppose the Stream = 1 {...} block indicates multiStream.
> Pete> It looks as if the encoder is ignoring my oneStream and sending multiStream
> Pete> in it's place. Is there something I missed and ought to be doing?
> 
> You have not missed anything.
> 
> Once upon the time I thought that it would be convenient for the user
> if the decoder abstracted away the syntactic sugar for the default
> stream id (oneStream). But now I realize that it is pretty confusing.
> 
> If you download and gunzip the attached file into the megaco/src/text
> directory and recompiles megaco/src/megaco_text_parser.erl I think
> that the decoder to behave like you expected.
> 
> /Håkan






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