Subject: [MMUSIC] Crazy SDP based on a=rid lack of syntax restrictions.

From: Magnus Westerlund <[email-masked]>
Date: Tue, 5 May 2020 09:16:40 +0000

Hi,

I sent an email on this already to C238 mailing list. However, I don't know if
got caught in the spam filters for people. Or that people don't know that things
may actually need feedback on postings on that list. I recommend people on that
list to keep their eyes open as we likely have some things for simulcast that we
need to share.  

So in the context of a=rid's syntax rules (See 
https://datatracker.ietf.org/doc/draft-ietf-mmusic-rid/)

You can also view it as an another installment in Cullen's how big can SDP
become? 

I think we still should have put in upper boundary for parameters in the ABNF
syntax in the RID (RFC8851). For example the rid-id we know have an implicit
upper boundary of 255 bytes otherwise it will not be possible to send as an SDES
item. And those integers for parameters (int-param-val) where catering for 64-
bit integers should be enough for all eternity. I guess this is a ship that
sailed. However, I do hope that your SDP parsers are capable of processing this
below example SDP snippet that I believe is syntactically correct and gives OPUS
a very high upper limit in bandwidth, i.e. restricted by codec and not RID
parameter. The value in the max-br parameter is Coleridge’s Rime of the Ancient
mariner(
https://www.poetryfoundation.org/poems/43997/the-rime-of-the-ancient-mariner-text-of-1834)
  in ASCII where each ascii character has been converted to octal encoding. It
is 55828 DIGITs.

   m=audio 49200 RTP/AVP 97 98 99 100 101 102
   a=mid:foo
   a=rtpmap:97 G711/8000
   a=rtpmap:98 LPC/8000
   a=rtpmap:99 OPUS/48000/1
   a=rtpmap:100 RED/8000/1
   a=rtpmap:101 CN/8000
   a=rtpmap:102 telephone-event/8000
   a=fmtp:99 useinbandfec=1; usedtx=0
   a=fmtp:100 97/98
   a=fmtp:102 0-15
   a=ptime:20
   a=maxptime:40
   a=rid:5 send pt=99,102;max-br=64000
   a=rid:6 send pt=100,97,101,102
   a=rid:7 send pt=99;max-

Cheers
 
Magnus Westerlund
-- 
Cheers

Magnus Westerlund 

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