[JDEV] File transfers

[Gallo, Felix S.]

Mike writes:
> Firstly, there is no inherent problem with sending moderately 
> large files through a software server. Sendmail does it all 
> day, every day, on a massive scale, without relying on 
> client-to-client connections.

However, most mail is accessed through POP, IMAP, or Exchange,
which are definitely client-to-client connections -- for the
simple reason that sendmail doesn't scale very well.  For
every byte send to a sendmail server, two bytes traverse the
network.  Most unfortunately, those two bytes always involve
just the one sendmail server and its attached network.

What positives do you get for having the sendmail server involved
in a large file transaction between two parties?  You get a
guarantee of delivery and no need for continued storage on the
sending party's side (since the file 'moves' to the sendmail server).
If you're sending the file to multiple users at once, you get less
traffic on your local network (the server takes the load).
You also get an opportunity to mediate the file somehow (e.g.,
virus checking it as a service, converting it from aac into mp3,
storing it for later delivery to other users..)

What positives do you get for not having the sendmail server 
involved?  The network on the sendmail server sees 0X load
rather than 2X load; the latency is lower; the sendmail server
has no storage requirement; and you have arguably fewer points
of failure.

Pragmatically, taking the load off the server is more valuable
in the normal case than replicating HTTP/FTP/SMTP/FXP yet again.
The fact that 'SMTP does it' is not a great rationale for forcing
all the jabber servers to pay 2X bandwidth costs for file transfers
between their users.

F.


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