Network Mail Observations

Mike Muuss (mike@BRL.ARPA)
Thu, 13 Feb 86 19:10:11 EST

some local, many not. (Statistics here are aproximate, from memory
rom the last time I looked, half a year ago). To handle incoming mail,
we permit two simultaneous SMTP servers; this seems fine.
To handle outgoing mail, our busier machines run from 3 to 5 deliver
processes. There are (strict) timeouts on all parts of the SMTP
dialog (different timeouts at different stages), so that none of the
delivery processes "hang up" for very long. This may have the occasional
side effect of "ganging up" on some recipient host. If that host is
also implementing a policy of limiting the number of inbound connections,
then this can't ever get too bad.

>From hours of watching the SMTP dialogs (in a spare window), it seems
to me that a lot of delivery time is spent engaged in the back-and-forth
validation of the recipient addresses, one at a time. With the majority
of our messages going to several people at any given site, and the very
long round-trip times through the core during the daytime (RTT from
MILNET in Maryland to ARPANET in California runs 3-12 seconds in the
daytime), this is a non-trivial factor. For people at the end of
low-bandwidth pipelines, the transmission of the data portion of the
message tends to take most of the time. (We require a recipient host
to accept data at a minimum rate of about 300 baud plus a constant,
or we timeout the transmission).

Overall, we feel that our mail system is pretty well balanced, and
represents a significant, but reasonable, load on our systems.
(If anybody cares, we run MMDF II and IIb on 4.2 and 4.3beta UNIX systems).

The single biggest improvement for our mail traffic would probably
come from better core gateway performance (jab jab).

The next biggest improvement would come from additional bandwidth
on our IMP (more trunks). And speaking of which, I heard a rumor that
a recent (last 3-4 months) change to the IMPs changed the behavior of
the IMPs w.r.t. traffic originating at the IMP -vs- through traffic.
(To more strongly favor through traffic). On the face of it, this
is probably the right thing to do for overall system optimization.
However, we noticed a SERIOUS loss of available bandwidth, a loss
which seems to have only partly been restored. Am I dreaming?


This archive was generated by hypermail 2.0b3 on Thu Mar 09 2000 - 14:35:40 GMT