[ENet-discuss] File transfers w/ e-net

[ryan.rogers at frontiernet.net]

Hi folks,

Yep, under ideal conditions, UDP can be great at file transfers.  For our render farm distribution here at work, I've written a file patcher which syncs directories across the network at uber-speeds by leveraging large frame transfers, and of course infrequent OOO's and virtually no drops.  It's about 35% faster than copying a file over SMB share!!!  When multicasting, it can be orders of magnitudes faster, as I can update 50 render nodes with one transfer of the data over the network.

However, this is on a high speed reliable LAN with fantastic switches, and I knew that when I started.

But what about less than ideal conditions, like the Internet, and servers that are starting to approach maximum thresholds?

One area you will run into problems is the lack of throttling due to packet loss under server or network duress.  The hosts can end up choking themsleves due to lack of ack's and multiple resends; a small problem ends up being amplified into a big one due to the protocol being dumb.  TCP has a fairly sophisticated implementation to provide this stream control.  If you roll your own on UDP, it's not-trivial to get one that works well under most scenarios, and when you are all said and done, you've essentially re-implemented a good bit of TCP, and it will have similar (or..egads!) worse performance.  

And if that is the eventual outcome, why did you bother to begin with?I don't like reinventing the wheel. ;-)

My advice is if I've got stream to copy over the Internet from a single source, chances are TCP or one of the app protocols built upon it (HTTP, FTP, etc) is the right choice.

Rhino

----- Original Message -----
From: "Kenneth Bull" <llubnek at gmail.com>
To: "Discussion of the ENet library" <enet-discuss at cubik.org>
Sent: Thursday, May 13, 2010 1:29:20 PM
Subject: Re: [ENet-discuss] File transfers w/ e-net

On 12 May 2010 19:46, Chris Jurney <jurney at gmail.com> wrote:
> Agreed.  You might look for something better suitted to transferring files
> than eNet like the File Transfer Protocol.  TCP has had a lot of effort
> poured into it to solve exactly this sort of problem.
>

Actually, using UDP for file transfers could give you a bit of a speed
boost.  If you send the file offset with each packet, the client could
assemble the file out of order and request missing blocks as needed.
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