From: ccie2be (ccie2be@nyc.rr.com)
Date: Tue Oct 21 2003 - 11:38:39 GMT-3
Hey Guys,
I don't remember all the details but Jonathan is right. Back in the old
days, when ethernet was first being developed as a shared medium, there had
to be a way to balance such issues as signal attenuation which limited the
total length of the cable and fair access to the meduim and speed of frame
tranmission.
At the time, 1500 mtu was choosen as good balance between these factors. If
you really want to know the nitty, gritty details, you can probably find
them on line at the IEEE site under 802.3
dt
----- Original Message -----
From: "Jonathan V Hays" <jhays@jtan.com>
To: "'Casey, Paul (6822)'" <Paul.Casey@o2.com>; <ccielab@groupstudy.com>
Sent: Tuesday, October 21, 2003 10:12 AM
Subject: RE: Small Question....MTU size
> Paul,
>
> Good question. I don't know the answer but I can give you an idea.
>
> I suspect the tradeoff had more to do with CSMA/CD timing back in the
> days when ethernet was run on a shared cable. If you were deciding on a
> specification, you would pick a stable clock rate (for example, 10 Mbps,
> just as a number pulled out of the air ;) which was dependent on the
> level of technology at the time (1970s I think) and a maximum cable
> length, and how long to listen on the cable before sending your frame
> (CSMA/CD). The size of the packet is obviously going to affect the
> timing for collision detection and avoidance.
>
> I think these are the factors that determined the maximum size of the
> ethernet frame in the original specs, but I'm admittedly just guessing.
>
> Maybe someone else knows more of the details.
>
> Jonathan
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> Casey, Paul (6822)
> Sent: Tuesday, October 21, 2003 6:04 AM
> To: ccielab@groupstudy.com
> Subject: Small Question....MTU size
>
>
> Hello,
>
> Can someone tell me why the MTU for IP networks is 1500 bytes.
> I konw that the standard for ethernet 1500, but I am wondering why this
> was
> picked..
> Why was an MTU of a1000 picked or what not an MTU of 5000.
> Also apart from ethernet why does the MTU of serial interfaces default
> of
> 1500 Bytes.
>
> Was this an optimal value for something..?? maybe a trade off between
> packet
> header overhead with small MTU and increasing number of errors with
> larger
> packets...??
>
> I have a problem getting a good answer for this, I asked one on the
> experts
> at work, but he said just thats the way it always was...???
>
> Any help appreicated.
> Kind regards.
> Paul.
>
>
>
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