[SOLVED] algorithm Say you want to transfer 1Kbyte (i.e. 8000 bits) frames over a 0.5 Mbps channel with a one-way delay of 32 ms, using the sliding window algorithm, with SWS = RWS.

Say you want to transfer 1Kbyte (i.e. 8000 bits) frames over a 0.5 Mbps channel with a one-way delay of 32 ms, using the sliding window algorithm, with SWS = RWS.
a) Compute the value of SWS that will ensure high channel utilization.
b) Suppose the sender will time-out at 1.5*RTT, and an ACK frame is sent for each correctly received, in-order frame (Ignore the transmission time of the ACK frame but do not ignore the propagation delay). Sketch a timeline diagram for the following case, labeling each data frame and ACK as F1, F2, and ACK1, ACK2, etc. (assume that there are enough bits in the sequence field in the header of the frame such that there is no need to wrap-around sequence numbers). Clearly label the time axis assuming the first frame F1 is transmitted at t = 0. No ACKs are sent for out-of-order frames.
CASE: F2 and F4 are lost (remember, frame lost means it did not reach the receiver)
We want to continuously be able to send frames in order to keep the link utilization 100% (i.e. keeping the pipe full)
(BW x Delay) product = 0.5 Mbps (232 msec) = 32 Kbits = 4 Kbyte Hence SWS = 4 KB/1KB = 4
b) The sequence of events are as follows:
Time (msec)
Event
Comments
0
F1 is transmitted
16
F2 is transmitted
This frame is lost
32
F3 is transmitted
This frame is received and buffered (but not acknowledged)
48
F4 is transmitted
The sender window has closed after transmitting this frame This frame is lost
64
ACK1 is received F5 is transmitted
The RTT is 64 msec. The Sender window size opened up one frame Sender send F5 and stops.
112
Timeout of F2
has expired. Sender send F2 again
This is just an assumption. The timeout is set at the time
the frame is transmitted. You could assume that the time out starts from the end of the transmission of the frame
128
Timeout of F3
has expired. Sender send F4 again
144
Timeout of F4
has expired. Sender send F4 again
160
Timeout of F5

has expired. Sender send F5 again
176
Sender receives ACK3 Send frame F6
Receiver has acknowledged both F2 and F3. Sender window Will open by two frames
192
Send frame F7
208
Sender receives ACK5
Receiver has acknowledged both F4 and F5. Sender window Will open by two frames and so on..