ATM question (a,b,c,d)

Here's a try:
a) transmission time for each switch, be it any switch (considering they are all of the same make) could be anything depending on the processing time of the switch. This is in a condition where the switch is not loaded with any other cell in the queque waiting to be transmitted. so in an ideal situation, when all the switch has to do is to transmit just ONE single cell, it would primarily depend on its ability to switch the cell to the next outgoing port (which is this case is a port connecting to the next switch). in reference to this context, this transmission time should be considered neglible against propagation time. if you read question (b) you would notice that is says "...if the switch is free our cell is transmitted immediatly". that can be a valid answer.
b) its asking the time interval between the particular cell reaching the first switch, traversing through the other switches in the middle and reaching the fifth switch. your propagation route is as follows, and i am also putting in the calculations to be done:

cell at switch 1 : (add processing time at switch 1, unless switch is free)

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> cell travelling to switch 2 : (add propagation delay between switch 1 & 2)
cell at switch 2 : (add processing time at switch 2, unless switch is free)

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> cell travelling to switch 3 : (add propagation delay between switch 2 & 3)
cell at switch 3 : (add processing time at switch 3, unless switch is free)

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> cell travelling to switch 4 : (add propagation delay between switch 3 & 4)
cell at switch 4 : (add processing time at switch 4, unless switch is free)

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> cell travelling to switch 5 : (add propagation delay between switch 4 & 5)
now you have been told to ignore propagation delays and switching time, so the only metric is the time taken in travelling between the switches i.e time taken to travel = 1&2 + 2&3 + 3&4 + 4&5 = 4X (transmission time)
your transmission time can be found out from your data rate which is 43 Mbps, and you do know that each cell is 53 bytes.
c) everything remains the same as above for this question, apart from the fact that you now have a switching time which is a variable between 0 to 60. so the switch is now busy, thus we have a switching or processing time. also note, the cell wait or cell switching time is one and a half of a single transmission time. so now you have a wait time that you can calculate from your transmission time. so calculate a total time for a non - busy path, and then with all the delays and the switching times, add them and divide them by 2, and you should have your average.
d) your delays are between 100% and 60%. so calculate using the probability, the minimum and the maximum time for delay, and calculate their average.

A couple of thoughts if you will on this topic. First of all queues. It was mentioned that RT-VBR is being used, placing your designated video traffic into queues that are serviced differently (high priority) than other traffic being processed by the switch. RT-VBR is configurable to control your burst "guaranteed" data rate and delay so as to control end to end delay and jitter...

Also, hardware characteristics of the ATM switch. Different switches have different capacities, ex. a smaller switch may be able to handle up to OC-48, but a larger switch may handle several OC-48. Switch processor speed, memory and capability of the switch ASICs all would have tangible effects.

That is why I don't think you can necessarily make a calculation for your delay, etc. because of so many contributing variables. Really, all you can do is run tests and observe the actual effects.

Please follow up with this, ambis, when your assignment is complete. I'd like to learn something new!