- Prove that the Stop-and-Wait
protocol will operate
correctly using
only
2 different sequence number
I.e.: you only need to label the frame in Stop-and-Wait using sequence numbers:
- 0 and 1
- A sender and a receiver is using the
Sliding Window protocol using
a send window size = 4 and
receive window size = 4
The ACK scheme used is cumulative ACK where ACK N acknowledges all frames upto (but not including) frame N
The sender transmits 4 frames to the receiver and 2 of the frames are received in error. (Recall that the receiver can use the CRC code in a frame to check if the frame is in error)
The following diagram show the transmitted frames:
Questions: what is the response of the receiver for these frames:
- Frame 3
- Frame 0
- Frame 1
- Frame 2
-
Suppose you are designing a Sliding Window
protocol for a
1 Mbps point-to-point
link to the moon.
The a one-way propagation delay between earth and moon is 1 sec.
Assume that the frame size is fixed and is equal to 1 KBytes, you can assume that 1 KBytes = 8000 bits.
You can assume the ACK frame is negligible.
Questions:
- Assuming there is no transmission errors,
and Sliding Window uses a send/receive window
size of
100,
what is the link utilization
(= channel utilization) ?
In other words: what fraction of the 1 Mbps link capacity is used to transmit data frames (10 pts)
- You cannot simply apply
the Stop-and-Wait utilization
formula.
- Take a look at how
the utilization in
Stop-and-Wait is
calculated
- Apply the logic to compute the utilization in Sliding Window
- You cannot simply apply
the Stop-and-Wait utilization
formula.
- Assuming there are
no transmission errors,
what is the minimum number of bits
you need for the sequence number
in the frame
that will allow you to use the
entire capacity of the link ? (10 pts)
Hint: find the smallest send window size that will allow the sender node to transmit continuously (i.e., without stopping)
- Assuming there is no transmission errors,
and Sliding Window uses a send/receive window
size of
100,
what is the link utilization
(= channel utilization) ?
-
A sliding window protocol uses the cumulative ACK scheme.
We will use a slightly different Acknowledgement scheme:
- ACK n will acknowledge the reception of all frames upto and including frame n.
(So you must adjust what you have learned to the above scheme !!!
The number of bits in the sequence number field is 3 (8 different sequence numbers).
A receive windows size and send window size is 5.
The initial send and receiver windows are {0,1,2,3,4}.
The following events occurs at the receiver in the given sequence:
- The receiver first receives
the frame numbered with seq. no. 3.
What ACK message (give sequence number) will the receiver
send back to the sender ? (2 pts)
- The receiver next receives
the frames numbered with seq. no. 0 and 2.
What ACK message (give sequence number) will the receiver
send back to the sender ? (2 pts)
- The receiver next receives
the frame numbered with seq. no. 1.
What ACK message (give sequence number) will the receiver
send back to the sender ? (2 pts)
- The receiver next receives
the frame numbered with seq. no. 0.
What ACK message (give sequence number) will the receiver
send back to the sender ? (2 pts)
- Is this frame always a retransmission or can this frame be
a new frame ?
Show your reason (with a diagram with frame receive/loss events) to get full credit. (5 pts)
- Is this frame always a retransmission or can this frame be
a new frame ?
- The receiver
next receives the frame numbered with
seq. no. 1.
What ACK message (give sequence number) will the receiver
send back to the sender ? (2 pts)
- Is this frame always a retransmission or can this frame be
a new frame ?
Show your reason (with a diagram with frame receive/loss events) to get full credit. (5 pts)
- Is this frame always a retransmission or can this frame be
a new frame ?
- Repeat Question 4 using the following changes in the
sender and receiver:
- Sender window size = and Receiver window size = 4
- The initial sender/receiver window = {0,1,2,3}