Current street prices for US Internet Transit

Wed Aug 18 04:13:42 UTC 2004

On Tue, 17 Aug 2004, Deepak Jain wrote:

> Maybe I am wrong here, but what does the router's packet buffers have to 
> do with a TCP stream? Buffers would add jitter and latency to the pipe. 

Have you tried running a single TCP stream over a 10 meg ethernet with a 5
megabit/s policer on the port? Do that, figure about what happens and
explain to the rest of the class why this single TCP stream cannot use all
of the 5 megabit/s itself.

> Wouldn't a 5Gb/s TCP stream over 3000+ miles imply huge buffers on the 
> sender and receiver side? Since when do the routers buffers make a 
> difference for that? If your application is such that jitter and latency 
> don't matter, buffers are great. If dropping a packet on congestion is 
> worse than queuing it, also great. But how does that improve the 
> stream's performance otherwise?
> 
> "What happens when ports go full" are you implying some kind of HOL 
> problem in the 7600?

I'm implying that a 7600 with non-OSM doesn't have more than a few ms of
buffers making a single highspeed TCP stream go into saw-tooth performance
mode via it's congestion mechanism being triggered by packet loss instead
of via change in RTT.

Yes, the GSR/juniper with often 500+ ms buffers are often of no use in
todays world, but it's nice to have 25ms buffers anyway, so TCP has some
leeway.

If you have thousands of TCP streams it doesn't matter, then small packet
buffers will simply act as a high-speed policer when the port goes full
and they'll be able to fill the pipe together anyway.

-- 
Mikael Abrahamsson    email: swmike at swm.pp.se