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

Christian Groves <Christian.Groves@nteczone.com> Tue, 30 September 2014 12:48 UTC

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Date: Tue, 30 Sep 2014 22:48:00 +1000
From: Christian Groves <Christian.Groves@nteczone.com>
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Archived-At: http://mailarchive.ietf.org/arch/msg/mmusic/XITp75fEE2v_TvxYzCLzKOHzJ54
Subject: Re: [MMUSIC] draft-ietf-mmusic-sctp-sdp-07 SCTP SDP syntax question
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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. Also "space" should be SP to be 
> consistent with RFC4566.
>
> 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
>
> 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?
>
> 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.
>
> 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.
>
> 7) Cl.10: How will this registry relate to the “WebSocket Subprotocol 
> Name Registry” 
> (http://www.iana.org/assignments/websocket/websocket.xml#subprotocol-name)?
>
> 8) Cl.8.2: What's the significance of the the "*" in the examples in 
> terms of "association usage"?
>
> Regards, Christian
>
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