I know the reason for two of three.
1) Why is the Ethernet minimum frame size of 64 bytes?
Ethernet timing is based upon "bit time" the time a bit takes to travel the
distance of an maximum Ethernet segment length 100m or 328 ft. The minimum
frame size 64 bytes equals 512 bits or 512 bit times to travel the wire.
This has to do with a host on one end of the wire listening to use the wire
and another host on the opposite end transmitting. Note: This does not
include the Preamble.
2) Why is the Ethernet maximum frame size of 1518 bytes(not 1526)?
I guess for a similar reason. Remember most Ethernet implementations are
share media. So everyone host is contending for access to the wire. That
is why Ethernet is contention based and Token Ring & FDDI are deterministic.
A packet to large would actually allow less hosts per segment to transmit
their data in a timely fashion.
3) Why is the ATM frame size 53 bytes?
I do know exactly why 53 bytes was picked. I do know why a small frame size
was picked. A ATM packet has two parts: Address and Payload. The Address
is 5 bytes long and the Payload is 48 bytes longs. ATM was designed as a
Multi-service access medium, i.e. to handle Data, Voice, and Multimedia
content. The "Holy Grail" of voice transmission is delay and jitter. When
the Delay in voice transmission is more than 250ms, humans start talking
before the other person has finished. Resulting in a garbled conversion.
It takes less time to fill small frames with data. All the frames are the
same size so the transmission time, for a given network, is constant. QoS,
Quality of Service, features are implemented in ATM to guarantee delivery of
time sensitive frames like voice.
I hoe this helps. A good Ethernet book with some ATM and FDDI information
is Switched, Fast, and Gigabit Ethernet ISBN: 1-57870-073-6
-dlb
"azhar mumtaz" <[EMAIL PROTECTED]> wrote in message
[EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
> Hello Guys:
> What i want to know is why there is a limit that ethernet frame size
cannot be
> less than 64 bytes and more than 1526 bytes. I know that this is how
ethernet
> should be understand but whats the logic behind it. Similarly why we are
> limiting cell size of ATM to 53 bytes.
> Regards
> Azhar Soomro
>
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