[MUD-Dev] datagrams

[Ola Fosheim Grøstad <o.f.grostad@notam.uio]

Steve Houchard wrote:
> * If you don't put in congestion control (recovery/avoidance) you're not
> doing it right; I forward flames to the TCP-friendly homepage at:
> 
>         http://www.psc.edu/networking/tcp_friendly.html
> 
> Unless you've written such a system or studied these topics it will be
> time consuming and frustrating to write these bits.

ACK, I have read some of the stuff by now, but I am not sure if I will
be as nice as mister Mahdavi wants me to be ;^).  I think I would go for
something simple, as I don't expect to use much bandwidth and have to
send messages with priority (such as personal tells). Maybe it would be
sufficient to switch to lower resolution graphics and such when I sense
packet loss above a certain level, then slowly increase resolution...?

> (at least, last time I checked).  Every time you frag a packet it's
> chances of reaching the destination become exponentially lower.  You'll
> probably be safe with packet sizes of 128 or 256 bytes.

Mahdavi and Floyd writes the following on a webpage ("TCP-Friendly
Unicast Rate-Based Flow Control"):

        The MTU may be determined using an MTU discovery
        algorithm[RFC1191], or may be assumed to be the minimum
        acceptable value for TCP of 576 bytes.

I guess this means that even 512 bytes is pretty safe? That would indeed
be convenient.

> * Sending multiple copies of packets when unneeded is probably not a good
> use of bandwidth.  Reasong being that "bad weather" usually means
> "congested router" and blasting more packets through that router isn't
> likely to help (typically it makes things even worse).  IMHO a fast
> recovery with exponential backoff SACK system is the best way to go
> although I tend to be a little biased towards SACKs :)

Well, you did at least make me read rfc2018. Isn't what you describe
rather TCP centric?  I figured that it would be a good idea to send ACKs
multiple times to avoid unnecessary resending of data (which tends to be
much larger than the ACKs).

> Unfortunately, my code is now property of the Regents of the University of
> Michigan so I'm not able to pass that along (not that the code is
> particularly good anyway).  I can post packet formats and issues I've run
> across in my own code though--just give the word.

Abstract descriptions and issues are almost certainly very very useful
and welcome! :)

--
Ola -  http://www.notam.uio.no/~olagr/





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