Questions about Internet Packet Losses

Bob Metcalfe metcalfe at
Mon Jan 13 21:08:59 UTC 1997

Hello, and best wishes for what's left of 1997.  Now, if you would, ...

Below are some questions I hope you'll help me answer about packet loss on
the Internet.

Here are two paragraphs taken from:

"Early experiments with NetNow show that 30% packet loss between public
exchange points is common for major Internet service providers during peak
usage periods. The initial investigation also suggests that loss rates are
closely related to bandwidth usage and congestion problems. Although some
of the packet loss is inadvertent, a large percentage of the public
exchange point connectivity problems reflect intentional engineering
decisions by Internet service providers based on commercial settlement

"The high packet loss may not generally reflect problems seen by the
majority of customers of the larger network service providers. In fact,
increasing levels of Internet traffic are not traversing the public
exchange points. Instead, many large service providers are migrating their
inter-provider traffic to private exchange points, or direct connections to
other providers. Merit is working closely with providers to develop tools
and infrastructure that more closely reflect Internet performance as
observed by the majority of backbone customers."


Are you familiar with this packet loss data from Merit?  If not, please see
above URL.

Is Merit's packet loss data (NetNow) credible?  Do packet losses in the
Internet now average between 2% and 4% daily?  Are 30% packet losses common
during peak periods?  Is there any evidence that Internet packet losses are
trending up or down?

If Merit's data is not correct, where has Merit gone wrong?  Where is there
better data?

Were Merit's data correct, what would be the impact of 30% packet losses on
opening up TCP connections?  On TCP throughput, say through a 28.8Kbps
modem?  On Web throughput, since so many TCP connections are involved?  On
DNS look-ups?  On email transport?

How big a problem is HTTP's opening of so many TCP connections?  Does TCP
need to operate differently than it does now when confronted routinely with
30% packet losses and quarter-second transit delays?  What is the proper
response of an IP-based protocol, like TCP, as packet losses climb?  Try
harder or back off or what?  How robust are various widespread TCP/IP
implementations in the face of 30% packet loss and quarter-second transit

Is the Internet's sometimes bogging down due mainly to packet losses or
busy servers or what, or does the Internet not bog down?

What fraction of Internet traffic still goes through public exchange points
and therefore sees these kinds of packet losses?  What fraction of Internet
traffic originates and terminates within a single ISP?

Where is the data on packet losses experienced by traffic that does not go
through public exchange points?

If 30% loss impacts are noticeable, what should be done to eliminate the
losses or reduce their impacts on Web performance and reliability?

Are packet losses due mainly to transient queue buffer overflows of user
traffic or to discards by overburdened routing processors or something else?

What does Merit mean when they say that some of these losses are
intentional because of settlement issues?  Are ISPs cooperating
intelligently in the carriage of Internet traffic, or are ISPs competing
destructively, to the detriment of them and their customers?

Any help you can offer on these questions would be appreciated.

/Bob Metcalfe, InfoWorld


Dr. Robert M. ("Bob") Metcalfe
VP Technology, International Data Group

InfoWorld columns:
Mail: metcalfe at
Telephone: 617-534-1215

Conference Chairman for
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