Klarinet Archive - Posting 000266.txt from 1995/08

From: Robin Fairbairns <Robin.Fairbairns@-----.UK>
Subj: Re: A technical question
Date: Mon, 21 Aug 1995 04:17:16 -0400

Rich Copeland <RichC611@-----.COM> writes:

> Here's the situation: John posts a question or comment. Mary
> follows this with a reply. Sometimes, when I am reading through
> my Klarinet messages, Mary's reply shows up first, followed by
> John's question. Occasionally, I only see Mary's reply! Could
> anyone explain this? I use a feature in AOL which downloads
> all the incoming e-mail messages and allows me to read them
> at my leisure, off-line. I do not use the "digest" system, I leave
> the individual messages intact.

Welcome to the exciting world of electronic mail.

While it's `better than it used to be' (TM), the system is still not
entirely reliable, and mail does get lost, (rarely) stolen, or simply
delayed.

Mail gets lost because servers crash while transmitting it (they
_should_ create databases that prevent loss in this circumstance, but
not all do, and not all that do so, do so reliably); because routers
send it off to a black hole as a result of a transient network
failure; because your system drops it on the floor (not even AOL is
entirely reliable...).

Mail mostly nowadays gets delayed by transient network effects.
Suppose your mail is travelling from A to D in the picture below:

--- B ---
/
A D
/
--- C ---

and suppose ABD is the `fast route' that's normally used; then if B
crashes at the point that John's message is about to be transmitted,
then his message will be (slowly) routed ACD. Now, Mary's copy of the
original goes by an entirely different path, and by the time her reply
arrives, B is working again, so her reply is (quickly) routed ABD, et
voil`a!

Worse things (by far) happen on Usenet, which uses entirely different
routing mechanisms ... count yourself lucky.

R