I was reading Data Communications and Networking by Behrouz A. Forouzan in which for simple Aloha protocol the vulnerable time given was T(fr) (time required to send out a complete frame on the channel) and 2T(fr) for slotted aloha protocol.

And for CSMA vulnerable time given was T(p) i.e. propagation delay.

My question is which of the 2 protocol is better in terms of vulnerable time or generally speaking which is smaller T(fr) or T(p) ?

1 Answer 1


The answer is -- it depends.

T(fr) or serialization delay, is the time it takes to send on frame on the wire. It is dependent on both the size of the frame and the bandwidth (speed) of the media. A 1000 bit frame takes 1 mS on a 1 Mpbs media (1e3/1e6).

Propagation delay is dependent on the speed of electricity in the circuit (depends on the type -- fiber or copper plus any intermediate switching delays) and the length of the circuit.

So without knowing those parameters, your question is unanswerable.

  • Thanks! This is what I was looking for :) Sep 2, 2020 at 16:58
  • Is serialization delay a common terminology because I guess forozon or tannenbaum didnot mention this in their books. Sep 2, 2020 at 17:14
  • Yes. If the answer is useful, please accept so it doesn't keep popping up looking for an answer.
    – Ron Trunk
    Sep 2, 2020 at 17:21

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