On Sun, Aug 27, 2006 at 04:33:15PM +1200, Ian McDonald wrote:
> Burak wrote on the Linux DCCP mailing list:
> >> After applying Ian's patches (except for bestpacketnext) I did some
> >tests with ccid3 and came across a problem. In some cases when packet loss
> >occurs, transmit rate drops down and stays there, with almost no increase.
> >Besides, p value is set to a value bigger than zero after the loss, and
> >does not change again, although no loss occurs - which may be the
> >explanation of the unchanging tx rate ???
> >
>
> I have a question for people. If DCCP detects loss once and once only
> (as I suspect is happening here (Burak - can you confirm through a
> packet trace please?) then I haven't read anything in the spec of TFRC
> or CCID3 which says that you can lower the loss rate later on when you
> don't have a loss. As I read the spec you only recalculate the loss
> rate when you get a loss and thus if you have a loss when you are
> starting you have a real issue.
Hi Ian,
I beleive you need to recompute the loss rate on every received data packet.
While there is no packet loss, the average loss interval will increase and
p will decrease.
This is because we take into account the interval between the lastest loss
event and the current sequence number if it helps us increase the rate.
RFC 3448:
"When calculating the average loss interval we need to decide whether
to include the interval since the most recent packet loss event. We
only do this if it is sufficiently large to increase the average
loss interval."
Without this, TFRC will never push the rate up to find newly added bw, unless
it is in slowstart ofcourse.
Best regards
--
Programmer
Edgar E. Iglesias <edgar.iglesias@xxxxxxxx> 46.46.272.1946
