5. Calculate the latency (from first bit sent to last bit received)
for the following:
a) 10-Mbps Ethernet with a single store-and-forward switch in the
path, and a packet size of 5000 bits. Assume that each link introduces
a propagation delay of 10 µs and that the switch begins retransmitting
immediately after it has finished receiving the packet.
b) Same as (a) but with three switches.
c) Same a (a) but assume the switch implements ?cut-through?
switching: It is able to begin retransmitting the packet after the
first 200 bits have been received.

Hi again!!

a) 10-Mbps Ethernet with a single store-and-forward switch in the
path, and a packet size of 5000 bits. Assume that each link introduces
a propagation delay of 10 µs and that the switch begins retransmitting
immediately after it has finished receiving the packet.

propagation delay = 10 µs = 0.00001 s 

We have one switch, then there are two links.

Latency = propagation delay of links + transmit delay of links =
        = 2 * propagation delay + 2 * Packet Size/Bandwidth =
        = 2 * 0.00001 s + 2 * (5000/10000000)s =
        = 0.00002 s + 0.001 s =
        = 0.00102 s =
        = 1.02 ms

----------------------------------------------------------

b) Same as (a) but with three switches.

The problem is the same as the above but now we have 4 links: 

Latency = propagation delay of links + transmit delay of links =
        = 4 * propagation delay + 4 * Packet Size/Bandwidth =
        = 4 * 0.00001 s + 4 * (5000/10000000)s =
        = 0.00004 s + 0.002 s =
        = 0.00204 s =
        = 2.04 ms

----------------------------------------------------------

c) Same a (a) but assume the switch implements ?cut-through?
switching: It is able to begin retransmitting the packet after the
first 200 bits have been received.

We have one switch again, then there are two links.

With cut-through the switch delays the packet by 200 bits, this means
a cut-through delay of:
Cut-through packet Size/Bandwidth = (200/10000000) s =
                                  = 0.00002 s =
                                  = 0.02 ms 

Latency = propagation delay of links + transmit delay + cut-through delay =
        = 2 * propagation delay + Packet Size/Bandwidth + 0.00002 s =
        = 2 * 0.00001 s + (5000/10000000) s + 0.00002 s =
        = 0.00002 s + 0.0005 s + 0.00002 s =
        = 0.00054 s =
        = 0.54 ms 

----------------------------------------------------------

I hope that this helps you. Feel free to request for a clarification
if you need it. I will gladly respond your requests.


Regards.
livioflores-ga

Hi livioflores-ga,

This is just to tell you that your answers are great. look forward to
working with you again.