[e2e] A implementation question on TFRC algorithm

[Phelan, Tom]

Hi Heejune,

The DCCP implementation of TFRC (CCID3, see draft-ietf-dccp-ccid3-05.txt) uses a "window counter", sent with each packet.  It's a four-bit counter that's increased once each quarter-RTT.  So the receiver interprets each increase of four in the counter value (with wrap) as a round trip time.

It's actually a little more complicated than the above explanation, so see the draft if you need the details.

Tom Phelan

> -----Original Message-----
> From: Magnus Westerlund [mailto:magnus.westerlund at ericsson.com]
> Sent: Monday, July 05, 2004 4:48 AM
> To: Heejune AHN
> Cc: end2end-interest at postel.org
> Subject: Re: [e2e] A implementation question on TFRC algorithm
> 
> 
> Hi Heejune,
> 
> I think the missing question here is, what transport protocol are you
> trying to implement TFRC over? RTP/UDP? In that case you will 
> have some
> problems. Standard RTP does not have sufficient information 
> to implement
> TFRC over. You will require certain extensions, and also there is the
> big question if your manage to get the feedback to report frequently
> enough per the TFRC requirements.
> 
> The IETF AVT WG are currently looking into what would be required to
> implement TFRC over RTP. There is an initial proposal in the draft:
> http://www.ietf.org/internet-drafts/draft-ietf-avt-tfrc-profile-00.txt
> 
> Please note that this is very initial work and will require more
> discussion.
> 
> Cheers
> 
> Magnus
> 
> Heejune AHN wrote:
> 
> >  Hi,  while implementing a streaming server, I am currently 
> doing TFRC 
> > transport adaptation module.
> >  
> > After reviewing several papers of Sally Floyd and A. 
> Zakhor,  I sill 
> > cannot implement it just because
> > I cannot understand one thing:
> >  
> > "How to calculate Round-trip time in Receiver?"
> > --------------------------------------------
> > it is written in her paper how to get Roud Trip time in 
> Sender, measuing 
> > the feedback for same sequence num.
> > (now my quetion, when the Rx decide to reply it?)
> >  
> > I need this value because
> > "Rx should report feedback to the sender at least once per 
> round-trip 
> > time if it has received packets in that interval"
> > (page 3 of SIGCOM 2000  publication, Equation-based 
> Congestion control 
> > for Unicast Application, Sally Floyd et al).
> > I checked it from D. Tan and A. Zakhor papers in IEEE multimedia, 
> > but the mechanism is not clear.
> >  
> > Maybe I can check with Sally's ns-2 simulation script, but 
> it is too 
> > much her computer-setting dependent script.
> > I think it is not a big problem on their work, but I just 
> want to know 
> > how they implemented it.
> >  
> > Thanks.
> >  
> 
> -- 
> 
> Magnus Westerlund
> 
> Multimedia Technologies, Ericsson Research EAB/TVA/A
> ----------------------------------------------------------------------
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> 
>