Rounding out the discussion is Jim Gettys, who edited the HTTP/1.1 specification and was a co-designer of the X Window System. He now is a member of the technical staff at Alcatel-Lucent Bell Labs where he focuses on systems design and engineering, protocol design, and free software development.

 

Vin T ceRf: What caused you to do the analysis that led you to conclude you had problems with your home network related to buffers in intermediate devices?

illustration by John balestrieri based on a PhotograPh courtesy of Vint cerf

JiM GeTTys: I was running some bandwidth tests on an old IPsec ( Internet Protocol Security)-like device that belongs to Bell Labs and observed latencies of as much as 1. 2 seconds whenever the device was running as fast as it could. That didn’t entirely surprise me, but then I happened to run the same test without the IPsec box in the way, and I ended up with the same result. With 1.2-second latency accompanied by horrible jitter, my home network obviously needed some help. The rule of thumb for good telephony is 150-millisecond latency at most, and my network had nearly 10 times that much.

My first thought was that the prob-
lem might relate to a feature called
PowerBoost that comes as part of my
home service from Comcast. That led
me to drop a note to Rich Woundy at
Comcast since his name appears on
the Internet draft for that feature. He
lives in the next town over from me, so
we arranged to get together for lunch.
During that lunch, Rich provided me
with several pieces to the puzzle. To
begin with, he suggested my problem
might have to do with the excessive
buffering in a device in my path rather
than with the PowerBoost feature. He
also pointed out that ICSI has a great
tool called Netalyzr that helps you fig-
ure out what your buffering is. Also,
much to my surprise, he said a num-
ber of ISPs had told him they were run-
ning without any queue management
whatsoever—that is, they weren’t run-
ning RED on any of their routers or
edge devices.

Vin T ceRf
The key issue
we’ve been talking
about is that all this
excessive buffering
ends up breaking
many of the timeout
mechanisms built
into our network
protocols.
That gets us to
the question
of just how bad
the problem really
is and how much
worse it’s likely
to get as the speeds
out at the edge
of the net continue
to increase.