Re: [MMUSIC] draft-ietf-mmusic-sctp-sdp-07 SCTP SDP syntax question

Salvatore Loreto <salvatore.loreto@ericsson.com> Wed, 01 October 2014 07:29 UTC

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From: Salvatore Loreto <salvatore.loreto@ericsson.com>
To: Christian Groves <Christian.Groves@nteczone.com>
Thread-Topic: [MMUSIC] draft-ietf-mmusic-sctp-sdp-07 SCTP SDP syntax question
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Date: Wed, 1 Oct 2014 07:29:32 +0000
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Subject: Re: [MMUSIC] draft-ietf-mmusic-sctp-sdp-07 SCTP SDP syntax question
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Hi Christian,

thanks a lot for reading and reviewing the draft 
see more in line

On Sep 30, 2014, at 3:48 PM, Christian Groves <Christian.Groves@nteczone.com> wrote:

> I seemed to have got cut and paste happy in 1) below. The "1*(SP sctp-fmt)" should only apply to "DTLS/SCTP".
> 
> Christian
> 
> On 30/09/2014 10:12 PM, Christian Groves wrote:
>> Hello Salvatore,
>> 
>> There seems to be several issues with the updated syntax:
>> 
>> 1) Cl.4.1 Media Description: With the updated syntax the ability to have more than one usage of the SCTP association has been lost as "sctp-fmt" is a single value.


<Sal>
there have been several discussion about the ability to have more than one usage of the SCTP association, 
and has been agreed not to allow it.
So each 'm' line describes a single SCTP association;  each association has only one single specify usage.
</Sal>


>> Also "space" should be SP to be consistent with RFC4566.

<Sal>
thanks, you are right. I will correct it in my private copy, so it will appear correct in the next version. 
</Sal>

>> 
>> To address these I suggest the following update:
>> e.g.
>> sctp-m-line = %x6d "=" ("application" space sctp-port space "SCTP" 1*(SP sctp-fmt) CRLF) / ("application" space sctp-port space "SCTP/DTLS" 1*(SP sctp-fmt) CRLF) / ("application" space udp-port space "DTLS/SCTP" 1*(SP sctp-fmt) CRLF) sctp-port = port
>> 
>> sctp-fmt = association-usage
>> 
>> association-usage = token
>> 
>> 2) Cl. 4.1.1 sctp-port: The syntax for sctp-port indicates the dual use of "=", i.e.
>> 
>> sctp-port-attr = "a=sctp-port=" portnumber
>> port-number = port
>> 
>> That doesn't appear to be consistent with the example in clause 4 which has:
>> a=sctp-port 4060
>> 
>> To match that the syntax needs to be updated, something like:
>> 
>> sctp-port-attr = "a=sctp-port" SP portnumber
>> port-number = port
>> I'm not sure why "portnumber" is used when "port" is commonly used in clause 4.1?
>> 
>> The syntax could be simplified to:
>> sctp-port-attr = "a=sctp-port" SP port

<Sal>
good suggestion. I am including it in my private copy. 
</Sal>

>> 
>> 3) Cl.4.1.2: There appears to be a formal space (SP) missing from the syntax between association-usage and max-message-size.
>> 
>> sctpmap-attr = "a=fmtp:" association-usage [max-message-size]
>> 
>> should be:
>> sctpmap-attr = "a=fmtp:" association-usage [SP max-message-size]
>> 
>> The current syntax allows an fmtp usage with no max-message-size parameter, e.g. "a=fmtp:bfcp". Should this be allowed?

<Sal>
this has been discussed back in April or May. It has been decided that the max-message-size parameter is optional.
In the case it is not present the default value is 64K
</Sal>

>> 
>> 4) Cl.4.1.2: The last sentence of the 1st paragraph and the first sentence of the second paragraph appears to be a repeat.

<Sal>
got it. 
</Sal>

>> 
>> 5) Cl.4.1.2: "If the parameter is not present, the implementation should provide a
>> default, with a suggested value of 64K." Is this 64,000 or is 65,535 bytes?
>> 
>> 6) Cl.4, 4.1 and 10 refer to the <fmt> sub-field. These should be updated to refer to the <sctp-fmt> field.

<Sal>
got it. 
</Sal>

>> 
>> 7) Cl.10: How will this registry relate to the “WebSocket Subprotocol Name Registry” (http://www.iana.org/assignments/websocket/websocket.xml#subprotocol-name)?

<Sal>
It is not related. The 'association-usage' specifies how the SCTP association will be used.
For example in the case of webrtc-datachannel value it would indicate how to pair certain streams,
how to consider specific stream etc.
as described in https://tools.ietf.org/html/draft-ietf-rtcweb-data-protocol-08 and in 
http://tools.ietf.org/wg/rtcweb/draft-ietf-rtcweb-data-channel/

the WebSocket Subprotocol Name Registry is used to populate the protocol field in the
protocol field in https://tools.ietf.org/html/draft-ietf-rtcweb-data-protocol-08#section-5

</Sal>

>> 
>> 8) Cl.8.2: What's the significance of the the "*" in the examples in terms of "association usage"?

<Sal>
good catch I will clarify it.
</Sal>

>> 
>> Regards, Christian
>> 
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