Hello, please see the question file

CIS 527 Homework #2,

1. (10 points) Sketch the NRZ, Manchester, and NRZI encoding for the bit stream 010111110000. Assume that the NRZI signal starts out low.

1. (5 points) show the 4B/5B encoding, and the resulting NRZI signal, for the following bit sequence: 0000 0001 0101 1111

1. (10 points) A bit stream 10110101 is transmitted using the standard CRC method. The generator polynomial is x3+x+1.

1. 1. Show the actual bit string transmitted.

   2. Suppose the leftmost bit (the first bit) is inverted due to noise on the transmission link. Show that this error is detected at the receiver’s end.

1. (20 points) For a sliding window algorithm with SWS=5 frames and RWS=5 frames, the receiver use cumulative ACKs. Use a timeout interval of about 2 x RTT. Assuming that the transmit time of a frame is equal to 0.2 RTT and the frames are processed instantaneously if they arrive in order.

1. 1. (2 pts) What is the maximum number of frames that can be transmitted in one RTT?

   2. (2 pts) What is the smallest value for MaxSeqNum (the number of available sequence number)?

   3. (8 pts) Draw a timeline diagram (up to frame 7) for the situation when the Frame 2 is lost.

   4. (8 pts) Now, assume that the receiver sends a duplicate acknowledgement if it does not receive the expected frame. For example, it send DUPACK[2] when it expects to see FRAME[2] but receives FRAME[3] instead. Retransmission takes place either upon receipt of the first DUPACK or upon timeout. Draw a timeline diagram (up to frame 7) for the situation when the Frame 2 is lost.

Note for part 3&4: On each data frame and ACK frame, you need to indicate the sequence number (start from 0). In addition, you need to indicate what action is taken by the receiver when a frame is received, for example, processed, buffered, or discarded.

1. (10 points) Suppose that we run the sliding window algorithm with SWS = 5 and RWS = 3, and no out-of-order arrivals.

   1. Find the smallest value for MaxSeqNum. No explanation

   2. For this condition, give an example showing that MaxSeqNum – 1 is not sufficient

   3. State a general rule for the minimum MaxSeqNum in terms of SWS and RWS.

1. (10 points) Suppose you are designing a sliding window protocol for a 10 Mbps point-to-point link to the moon, which has a one-way latency of 2.0 seconds. Assuming that each frame carries 5KB of data, what is the minimum number of bits you need for the sequence number if RWS = SWS?

1. (10 points) Consider building a CSMA/CD (the same protocol as Ethernet) network running at 1Gbps over a 200 meter cable with no repeaters. The signal propagation speed in the cable is 2.5 x 108 meter/sec. What is the minimum frame size in order to be able to detect collisions?

1. (15 points) Suppose two nodes, A and B, are attached to opposite ends of a 1000 meter cable, and that they each have one frame of 12,000 bits (including all headers) to send to each other. Both nodes attempt to transmit at time t = 0. Suppose there are three repeaters between A and B, each inserting a 20-bit (or 20 bit/10Mbps = 2 microseconds) delay. Assume the transmission rate is 10Mbps, and CSMA/CD with backoff intervals of multiples of 512 bits is used. After the first collision, A draws K = 0 and B draws K = 1 in the exponential backoff protocol. Ignore the jam signal and the 96-bit time delay.

1. What is the one-way propagation delay (including repeater delays) between A and B? Assume that the signal propagation speed is 2 x 108 m/s.

2. At what time is A’s packet completely delivered at B?

3. Now suppose that only A has a packet to send and that the repeaters are replaced with switches. Suppose that each switch has a 20-bit processing delay in addition to a store-and-forward delay (retransmission). At what time, is A’s packet delivered at B?