[REMINDER]Re: [Nrg-l] NRG Next Wednesday

Niky Riga inki at cs.bu.edu
Tue Oct 5 18:26:30 EDT 2004


So it seems like we are having NRG tomorrow at 4:00 at the graduate lounge.
We are trying to change the style of NRG, and make it more 
discussion-oriented rather than just a presentation, so please read the 
paper before coming:-)

Niky

Georgios Smaragdakis wrote:

> As there is no Colloquium next week, NRG will take
> place on Wednesday. I will present the paper "Sizing 
> Router Buffers" that appears in SIGCOMM 2004 and lead
> the discussion of possible extensions.
> 
> 
> Date: Wednesday October 6
> Time: 3:00pm
> Place: Grad Lounge
> 
> 
> paper info:
> -----------
> 
> link:
> http://www.acm.org/sigs/sigcomm/sigcomm2004/papers/p277-appenzeller1.pdf
> 
> "Sizing Router Buffers"
> by Guido Appenzeller, Isaac Keslassy, Nick McKeown 
> Stanford University
> 
> Abstract:
> 	
> All Internet routers contain buffers to hold packets during times of
> congestion. Today, the size of the buffers is determined by the dynamics
> of TCP's congestion control algorithm. In particular, the goal is to make
> sure that when a link is congested, it is busy 100% of the time; which is
> equivalent to making sure its buffer never goes empty. A widely used
> rule-of-thumb states that each link needs a buffer of size B = RTT X C,
> where RTT is the average round-trip time of a flow passing across the
> link, and C is the data rate of the link. For example, a 10Gb/s router
> linecard needs approximately 250ms X 10Gb/s = 2.5Gbits of buffers; and the
> amount of buffering grows linearly with the line-rate. Such large buffers
> are challenging for router manufacturers, who must use large, slow,
> off-chip DRAMs. And queueing delays can be long, have high variance, and
> may destabilize the congestion control algorithms.
> 
> In this paper we argue that the rule-of-thumb B = RTT X C is now outdated
> and incorrect for backbone routers. This is because of the large number of
> flows (TCP connections) multiplexed together on a single backbone
> link. Using theory, simulation and experiments on a network of real
> routers, we show that a link with n flows requires no more than B =(RTT X
> C) / sqrt{n}, for long-lived or short-lived TCP flows. The consequences on
> router design are enormous: A 2.5Gb/s link carrying 10,000 flows could
> reduce its buffers by 99% with negligible difference in throughput; and a
> 10Gb/s link carrying 50,000 flows requires only 10Mbits of buffering,
> which can easily be implemented using fast, on-chip SRAM.
> 
> 
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return will.


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