CSC460 Homework Set 5 — Fall 2001
Due: Tuesday, November 6
- A link has data rate 4 kbps and propagation delay 20 milliseconds.
For what range of frame sizes does Stop-and-Wait give an efficiency of at
least 50% ?
- What fraction of data rate is wasted on headers and re-transmissions for
Selective Repeat on a heavily loaded 50 kbps satellite link with 0.25 second
propagation delay. Frames are fixed
size containing 3960 data bits and 40 header bits, including a sequence
number and a piggybacked ACK.
There are no separate ACK frames, but there are separate 40-bit NAK
frames. The (data) frame error rate is 1%. Neglect the NAK frame error
rate. Sequence numbers have 8 bits.
Suppose that in the Selective Repeat protocol of the preceding question
there occurs a period of silence (absence of data to be sent) in just 1
direction. Assuming that the sender has a 1-second timeout for repeating
un-acknowledged frames, how many times,
on average, would each frame be sent in the other (busy) direction during
a period of silence in the 1 direction?
Assume that the receiver lacks a timer for detecting absence of reverse
- An error-free 64 kbps satellite link with 0.25 second
1-way propagation delay uses 512-byte data frames in 1
and tiny ACK frames in the other direction.
What is the maximum effective data rate
for a window of size 7?