Re: [Simple] I-DAction:draft-hellstrom-simple-text-transmission-00.txt

[Adam Roach <adam at nostrum.com>]

On 3/10/08 11:22 AM, Ben Campbell wrote:
>
> On Mar 10, 2008, at 10:59 AM, Adam Roach wrote:
>
>>
>> I think #4 is exactly the right way to do it -- send the real-time 
>> text over RTP; reiterate it on message boundaries in MSRP; and do 
>> some kind of correlation in the SDP to indicate that a specific MSRP 
>> stream is associated with the specific RTP stream.
>>
>
> I'm a little confused--if you have already sent it over RTP, why do 
> you need to reiterate it?
>
> Thanks!

RTP doesn't have defined semantics around message boundaries. The 
redundant information in MSRP overlays those semantics on top of the 
real-time text. (It will also repair any text lost over the text RTP 
channel, as text RTP merely sends text redundantly, whereas MSRP's use 
of TCP involves explicit acknowledgments).

Also, this kind of solution has nice incremental fail-back behavior: a 
client using this mechanism will end up negotiating a reasonable user 
experience with:

   1. Other clients using this mechanism (with full functionality)
   2. Clients that implement just MSRP but not RTP text (albeit without
      the realtime component)
   3. Clients that implement just RTP text but not MSRP (albeit without
      the message boundary component).

/a
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