[MMUSIC] Comments on ABNF in draft-petithuguenin-mmusic-ice-sip-sdp-01

[Magnus Westerlund <[e-mail]>]

Hi,

As part of the RTSP for NAT work I actually noticed an issue with the
ABNF that is defined for ICE in SDP.

>From Section 8.1:

   candidate-attribute   = "candidate" ":" foundation SP component-id SP
                           transport SP
                           priority SP
                           connection-address SP     ;from RFC 4566
                           port         ;port from RFC 4566
                           SP cand-type
                           [SP rel-addr]
                           [SP rel-port]
                           *(SP extension-att-name SP
                                extension-att-value)

   foundation            = 1*32ice-char
   component-id          = 1*5DIGIT
   transport             = "UDP" / transport-extension
   transport-extension   = token              ; from RFC 3261
   priority              = 1*10DIGIT
   cand-type             = "typ" SP candidate-types



Petit-Huguenin & KeranenExpires August 29, 2013                 [Page 9]

Internet-Draft             ICE SIP/SDP Usage               February 2013


   candidate-types       = "host" / "srflx" / "prflx" / "relay" / token
   rel-addr              = "raddr" SP connection-address
   rel-port              = "rport" SP port
   extension-att-name    = byte-string    ;from RFC 4566
   extension-att-value   = byte-string
   ice-char              = ALPHA / DIGIT / "+" / "/"

The issue is what is allowed in extension-att-name and
extension-att-value. They are listed here as byte-string. That is an
extremely wide allowance in what values to be included.

First of all it includes SP the character used for delimiting the
-att-name against the -att-value and the next set of name and value. I
can't see that one can allow that, and if one have values that includes
space, then they must be escaped.

Further I wonder if it wise to include the non-visible values from the
below 128 range of the byte. It might be okay, but some thought needs to
be put into this.

Cheers

Magnus Westerlund

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