[Tsvwg] Re: [e2e] Are you interested in TOEs and related issues

[Alexandre L. Grojsgold]

>
> The problem is that in today's routers the buffer sizes are typically
> accounted in packets, not in bytes. So looking at your example, and
> supposing that the line card buffer is limited to 100 packets, a burst
> of small frames will instantly consume 13% of available buffer slots,
> while jumbos will only use 2%. This is of course no problem if the line
> card can transmit all those frames instantly, but what if it cannot?


So what?

Small packets get more buffer frames, but are also more rapidly sent.
The gueue grows fats, but shrinks fast too. It means that a burst of small
packets will not increase the packet loss, no mather the length of the
buffer (in packets) .

Ok, if the router gets a large amount of packets, representing more bytes
per second than the capacity of the output line, packets will be lost. But
it is a function of the amount of data conveyed by the packets, not of
their individual length.



>
>
> >
> > >> BTW, I asked a few transport folks in Minneapolis IETF about how
> > >> "evil" is traffic burst in today's enviroment, but did not get any
> > >> concrete answer. Perhaps this topic should be discussed in tsvwg
> > >> or tcpm.
> > >
> > >Because queues in todays routers have finite maximum lengths, and
> > > this model is unlikely to change in the forseeable future,
> > > excessive traffic bursts will be more likely subject to drop-tail
> > > policing than other kinds of more smoothly shaped traffic. More
> > > than that, the bursty traffic will not only have less chance of
> > > reaching its target with all fragments in place, but it will also
> > > most probably do much harm to


I think many people tend to thing about IP routers like old circuit
switched protocols switches, like X.25.


In circuit switched networks, flow control is generaly implemented in each
link, each pair of switches exchanging acks and naks, trying to keep data
at the right pace.


With IP, the flow control is end-to-end, performed by TCP. If a router
queues too many packets, it will break TCP stability. It is not an issue
of memory or memory price.


alg.