MTU of the Internet?

Phil Howard phil at charon.milepost.com
Fri Feb 6 00:42:15 UTC 1998


Steve Carter writes...

> Theory tells me that for both types of traffic it is probably better,
> for response times sake, to have an asymetrical MTU (send = smaller,
> receive = bigger from the clients perspective).  Servers set big MTU's,
> clients set their's smaller.
> 
> Irrespective of your MTU size, the file or web page, etc. size is always
> going to be the same, therefore, if you set a smaller MTU at the server
> or within the network, fragmentation occurs, meaning greater overhead
> for a file of a given size and due to this the end station will have to
> reconstitute the data stream out of smaller packets, meaning more CPU
> overhead.

I still think there has to be some kind of better approach to what it is
we are doing when we have such extreme ranges of bandwidth capacity and
the resultant extremes of optimal MTU.  One idea I'm thinking of, and I
may well even give it a try between a couple of Linux boxes over a phone
line, is what I call "cell multiplexed PPP".  Basically this would be a
channelized stream that can parallel multiple packets.  Small ones can
come right through while the big ones are still working.  That may only
help minimally for parallelizing image loading unless there is added
logic that detects the TCP ports and ensures that only one port at a
time is taking up a channel.

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