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

Christian Groves <Christian.Groves@nteczone.com> Tue, 30 September 2014 12:13 UTC

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Date: Tue, 30 Sep 2014 22:12:59 +1000
From: Christian Groves <Christian.Groves@nteczone.com>
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Subject: [MMUSIC] draft-ietf-mmusic-sctp-sdp-07 SCTP SDP syntax question
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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