[71767] in North American Network Operators' Group
RE: "Sizing router buffers" paper
daemon@ATHENA.MIT.EDU (Blaine Christian)
Wed Jun 23 10:39:45 2004
Date: Wed, 23 Jun 2004 10:38:57 -0400
From: Blaine Christian <blaine.christian@mci.com>
In-reply-to: <Pine.LNX.4.44.0406221943490.25077-100000@uplift.swm.pp.se>
To: 'Mikael Abrahamsson' <swmike@swm.pp.se>, nanog@nanog.org
Errors-To: owner-nanog-outgoing@merit.edu
> http://yuba.stanford.edu/~appenz/pubs/sigcomm-extended.pdf
>=20
> Anyone care to comment on this paper? I find that it confirms=20
> my beliefs and gut feeling I have had since 2000 or so, and=20
> my real life experiences with L3 switches with just a few ms=20
> of packet buffer.
I believe buffering is rather evil in a core network. A core network =
should
be designed such that very little buffering occurs. Vendors should =
provide
sufficient buffer to keep the link full at all times during congestion. =
Of
course the previous sentence is chock full of permutations and the size =
of
the buffer also depends on the amount of time you plan on spending
congested. If you are willing to deal with the delay you can shoot for =
some
protocol specific queuing strategies based on your customers needs. =20
I suspect that cost is another factor in the equation where a circuit =
may
cost more than the line card over the long run. Interestingly enough, =
this
equation has started to change with the fiber glut. If it is cheaper to =
run
your line cards at 100% all the time, instead of purchasing additional
capacity, then a well developed set of buffers and queuing mechanisms =
would
be appropriate (some traffic is not very sensitive to jitter/delay after
all).
I would beware the heavy reliance on TCP in this paper. I did not see =
much
mention of high throughput UDP/GRE/RTP for that matter. There are some
rather large and long lived non-TCP based flows nowadays. Many times =
the
flows are not nearly as friendly as TCP is. Some of the flows can be =
very
sensitive to buffering (RTP for VoIP for example). Unfortunately,
predicting where those flows will turn up is a difficult proposition
It would be interesting to find out if larger buffers help with DDOS =
issues.
I can see how we could assure traffic during short lived DDOS attacks =
with
the use of buffers but long lived attacks may not be dealt with as =
readily.
Regards,
Blaine
