Sally Floyd: Questions
- WHERE IS THE CONGESTION IN THE INTERNET?
What do we know about congested links in the Internet?
E.g., where is the congestion in the Internet? On access links to the
home or web server?
Transoceanic links? Wireless and satellite links?
Is the congestion on links with high
levels of statistical multiplexing, or on links with low
levels of statistical multiplexing?
How have the congestion points moved around as the Internet has
changed over the last ten years? Where do we expect the congestion
to be in the future, if anywhere?
Tools for learning about congested links:
- Venkata Padmanabhan and others have a series of papers on
Server-Centric View of Internet Performance: Analysis and
Implications that look at the question of identifying congested
links, or path segments, from packet traces taken at the web server.
Results include the following:
"In 45% of the cases, the identified lossy link crosses inter-AS
boundaries and has a high latency." A chart shows how many of the
identified non-leaf lossy links cross inter-AS boundaries, and how
many have high latency. "Only 20% of the lossy links neither cross
ISP boundaries nor have a high latency."
Anagnostakis, Greenwald, and Ryger,
On the Sensitivity of Network Simulation to Topology,
"We report that a mesurable fraction of packets pass through
multiple congestion points." A congestion point is defined not
in terms of packet drop/mark rates, but in terms of the distribution
of queueing delay. The rest of the paper shows that if you use
total aggregate goodput as the metric, then odd things happen
in simulation scenarios with multiple congestion points.
continent-to-continent packet loss rates on the SLAC web page
are for paths that
tend to use
reasonably well-provisioned transoceanic links from universities
or research institutes (e.g., the
StarLight, Abilene-AARnet, the KEK network, etc.).
The paths from Egypt, India, Hong Kong, South Africa, the Ukraine,
seem to use commercial routes, so the
packet loss rates from these countries are more representative of
Aditya Akella, Srini Seshan and Anees Shaikh,
Evaluating Wide-Area Internet Bottlenecks.
"We apply our measurement methodology to determine empirically the
locations, estimated available bandwidth, and delay of non-access
Mbarika, Jensen, and Meso,
Cyberspace Across Sub-Saharan Africa,
December 2002, CACM.
This paper doesn't have information about the congestion levels of
international links from Africa, but it does have information about the
increasing bandwidth of those links.
"Until recently few of the countries outside of South Africa had
international Internet links larger than 64Kbps, but today 23 countries
have links carrying 5Mbps or more, and 13 countries have outgoing links
of 10Mbps or more."
Improving Performance on the Internet,
CACM, February 2009.
"When it comes to achieving performance,
reliability, and scalability for commercial-grade Web
applications, where is the biggest bottleneck? In many
cases today, we see that the limiting bottleneck is the
middle mile, or the time data spends traveling back
and forth across the Internet, between origin server
and end user."
analyzes TCP dump files, and outputs a range of information about
each connection seen, including throughput, retransmissions, and
round trip times.
[ Sally Floyd].
Thanks to Senthilkumar Ayyasamy for additions to this page.
Thanks for Les Cottrell for information about the SLAC mesurements.
Last modified: February 2009