Although I agree that CN packets are a function of the media codec, they
*COULD* offer a mitigation to the effects of longer delay paths.
When the Path RTT is short (e.g. less than a tenth of a second), then
the "TFRC" algorithm already grows a window in a short time (e.g. still
much less than a second). Therefore the fact that CN packets are sent >
PRRT, isn't really an issue, the window will grow quickly anyway, we may
not need faster-restart...
When the PRTT is many tenths of a second or more, it can take many PRTT
to build a suitabel rate (i.e. long time), and the user would notice.
That's why we have faster-retransmit proposed. However, in the case of a
long path delay, a media codec that sends CN, will also effectively
"ping" the receiver, just as needed...
However, several things puzzle me, and I'd be interested in thoughts:
* Should DCCP/TFRC understand that CN corresponds to a "silent" period,
rather than a drop in the media rate?
* If CN is treated differently, what rules govern what counts as "ping"
and what counts as "data"?
* Should DCCP/TFRC set a maximum rate for these pings -- in the case of
a 1ms RTT, one packet every 4 RTTs is quite a lot!
Gorry
Magnus Westerlund wrote:
Arjuna Sathiaseelan wrote:
Any idea on how comfort noise packets could be used instead of ping
packets to solve this problem?
Hi,
I don't think comfort noise packets are the solution to this problem.
For many codec they have a fixed period, for example AMR sends one
silence descriptor packet every 8th frame, i.e. every 160 ms. Thus this
may remove the need for ping as long as the RTT stays in certain bounds.
However there is clearly cases where the RTT is so short that it would
not fulfill a goal of having a ping no less often than every 4th RTT.
One should also consider other traffic that may have characteristic that
makes it desirable to use faster restart but lacks comfort noise to send.
cheers
Magnus Westerlund
Multimedia Technologies, Ericsson Research EAB/TVA/A
----------------------------------------------------------------------
Ericsson AB | Phone +46 8 4048287
Torshamsgatan 23 | Fax +46 8 7575550
S-164 80 Stockholm, Sweden | mailto: magnus.westerlund@xxxxxxxxxxxx
