On 19/07/2011 21:08, Robert Sparks wrote:
Replying to just one part
On Jul 19, 2011, at 2:27 AM, Miguel A. Garcia wrote:
- Section 4.2 reads:
To remain backwards compatible with conventional SDP usage,
the format field of the m-line MUST have the arbitrarily-selected
value of "1".
The comment is that in other protocols, for example, MSRP [RFC4975] it
has been selected to use an asterisk "*" in the format field. I wonder if
it is possible to unify criteria, in order to allow usage of conventional
SDP parsers.
I don't see how this has any relationship to "conventional SDP parsers".
Any SDP parser should be able to parse the value "1", and the allowed
value is protocol-specific anyway. Since the values of the media and
protocol fields are completely different in our case, and because this
would break existing implementations of MRCP, I see no sufficient reason
to change the value.
Let me give you an example. If I have an SDP class that encodes SDP, the class would not be able to decide whether to
write an asterisk "*" or a "1" in the format field, when you invoke it. Writing "1" or
"*" will be dependent on the application.
Then, if you see an SDP body captured by Wireshark or similar, you will need to know
which application generated it before you could decided whether the SDP is correct or
not. And Wireshark will not be able indicate "format is irrelevant" until it
knows which application carried that SDP.
I haven't heard a good reason for keeping the value "1". So, I am still proposing to
reuse the "*".
Miguel - your SDP class will have to ask the application what the<fmt> field means
for a given<proto> field value _anyhow_ to populate it correctly.
Similarly, something like wireshark will have to recognize what is in
the<proto> field to do any higher level of verification beyond
the basic syntax in 4566 (which is to match a token as 4566 defines token, and
either * or 1 will match).
As Dan points out already there is deployed code that this change would break,
and I don't see the benefit you are arguing for.
RjS
Ok, I understand your motivation. Let's keep the draft as is in this aspect.
/Miguel
--
Miguel A. Garcia
+34-91-339-3608
Ericsson Spain
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