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With regards to Ethernet frames, the typical maximum size is 1500 bytes. Jumbo frames brought this up to 9000 bytes, and there was even some Super Jumbo Frames of sizes larger than that.

What factors are taken into account when determining these numbers? Is it simple math or is trial and error required to create a table of values then the equations as development of a protocol continues?

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    \$\begingroup\$ 1500 byte frame size came from the days of coax. It has to do with how long a packet travels from one end of the cable to the other end and other stations starting to send at the same time causing an collision. For details you'll have to search for documentation on 10Base5 and maybe 10Base2. \$\endgroup\$ – jippie Dec 11 '13 at 8:08
  • \$\begingroup\$ @jippie: actually, the minimum packet size is what is determined by the max time for the signal to travel back & forth: the sender has to be able to detect if collision happened and still be able to abort the packet. \$\endgroup\$ – Laszlo Valko Dec 11 '13 at 8:14
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There are several parameters of such a communication protocol that could be determined arbitrarily by the designers, however, these parameters do have some interdependence. Therefore what they do is they write the equations between the parameters, and see what combination results in all parameters being within an acceptable range.

There are basically two main reasons to limit the maximum packet length:

  • so that a reasonable amount of memory would be sufficient to implement the HW (these days 100KB is nothing but 30 years ago putting 100KB of RAM into a single Ethernet card would make it pretty expensive, and DMA-capable HW was also rare and expensive at that time),

  • to give other stations a chance to talk (the longer a single station can hold the communicational channel and the more stations you have, the longer it could take for a station to get any message to the channel).

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  • \$\begingroup\$ That's two easy to understand reasons. You may well have given me the answer. \$\endgroup\$ – Hamhot Ptonel Dec 11 '13 at 15:57

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