The Silent Scream: The Sad Story of Aborted Connections

Simon E Spero (
Tue, 13 Dec 1994 04:59:34 +0100

Executive summary:

Preliminary results show that Netscape aborts 8 times as many
connections as NCSA Mosaic, and that nearly a quarter of all
Netscape conceptions result in abortion.

A while ago I posted a message to www-talk describing problems caused by
aborted connections, and the difficulties involved in getting reliable
statistics on how often this problem was occuring.

Because it's so hard to gather these statistics through existing logs,
I made some minor modifications to tcpdump to add some HTTP 1.0 protocol
analysis, and ran a trace on all http traffic going over the primary
sunsite network. I only ran the trace for a relatively short period of time;
I'll be running a longer trace later this week. A brief analysis of the data
did yield some extremely interesting results.

I classified an aborted transaction as one in which the client sends a packet
containing a RST flag, and a successful transaction as one where the client
sends a packet containing a FIN flag.

The two most common clients as identified by a User-Agent flag in the HTTP
header were Mosaic (NCSA), and Mozilla(Netscape).


NCSA Mosaic 1,194 36 1,230 3%
Mozilla 1,004 313 1,317 24%