This sounds like a very interesting idea. While the documents specify
that feedback is sent once per RTT, since this is what TFRC
recommends, I think more frequent feedback is a fine idea even for
low-loss-rate/low-RTT scenarios (twice or four times per RTT, say?),
and probably mandatory for high-RTT scenarios. My guess is Sally
would agree. Perhaps someone could suggest a change to the CCID3/4
language.
TFRC (RFC 3448) only has a smalll discussion about sending multiple
feedback packets per RTT. E.g., in Section 6:
"If the sender is transmitting at a high rate (many packets per RTT)
there may be some advantages to sending periodic feedback messages
more than once per RTT as this allows faster response to changing
RTT
measurements, and more resilience to feedback packet loss."
TFRCbis (draft-ietf-dccp-rfc3448bis-02.txt) adds more clarification
about
what needs to be done when the receiver sends multiple feedback
packets per RTT. From feedback from Arjuna. In Section 6:
"If
the receiver was sending k feedback packets per RTT, step (4) of
Section 6.2 would be modified to set the feedback timer to expire
after R_m/k seconds. However, each feedback packet would still
report the receive rate over the last RTT, not over a fraction of
an RTT."
I think it is good to allow multiple feedback packets per RTT.
However, I personally wouldn't be inclined to make it the default
recommendation for all scenarios, for CCID 3/4, until there has
been a little more experience with it. Just in case there is some
drawback or implementation issue that pops up...
- Sally
http://www.icir.org/floyd/
