Subject: [MMUSIC] RFC3108 $ in c= line not supported by $ in m= line

From: "Ian Leighton" <[email-masked]>
Date: 17 Apr 2002 09:01:10 -0400

Hi All

Section 5.3 of RFC3108 indicates that the <networkType> parameter of the
c= line can be encoded as $. This section indicates that the purpose of
the $ is to allow a selection if a node interfaces to multiple networks.

Section 5.5.2 and the grammar of section 9 indicate that the <transport>
parameters of the m= line is NOT allowed to be encoded as $.

Is it possible to indicate via the rfc3108 SDP that the recipient choose
the c= line <networkType> and also choose the corresponding m= line
<transport> parameter?

Any comments/corrections/clarifications would be appreciated.

Regards
Ian

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From: "Rajesh Kumar" <[email-masked]>
Date: Thu, 18 Apr 2002 11:59:06 -0700

Ian,

RFC 2327 states:

   An announcement consists of a session-level section followed by zero
   or more media-level sections.

The m line is not mandatory. So you can wildcard the network type and omit
the 'm' line. This is how you can ask the recipient to select both network
type and transport.

There is another  means. You can set the transport and format to "-"  each.
Here is what RFC 3108 says about the use of "-":

   A "-" value indicates that it
   is not necessary to specify the value of the parameter in the SDP
   description because this parameter .... can be known from another source
   such as ..., another SDP
   descriptor or another part of the same SDP descriptor.

For an example, search for the string "m=audio $ - -" in RFC 3108.

The other SDP descriptor can, in this case, be the recipient's response
which includes the network type, transport and formats.

In this context, note the following RFC3108 ABNF:

	transport-fmts = generic-transport-fmts / known-transport-fmts / "- -"

Rajesh

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]]On Behalf Of
> Ian Leighton
> Sent: Wednesday, April 17, 2002 6:01 AM
> To: [email-masked]
> Subject: [MMUSIC] RFC3108 $ in c= line not supported by $ in m= line
>
>
> Hi All
>

Right, but there is the following possibility:

"-" indicated a don't care.