Section 8.7. Exercises | Computer and Communication Networks (paperback)

8.7. Exercises

1.	Consider a wide area network in which two hosts , A and B, are connected through a 100 km communication link with the data speed of 1 Gb/s. Host A wants to transfer the content of a CD-ROM with 200 Kb of music data while host B reserves portions of its 10 parallel buffers, each with the capacity of 10,000 bits. Use Figure 8.3 and assume that host A sends a SYN segment, where ISN = 2,000 and MSS = 2,000 and that host B sends ISN = 4,000 and MSS = 1,000. Sketch the sequence of segment exchange, starting with host A sending data at time t = 0. Assume host B sends ACK every five frames .
2.	Consider that host 1 transfers a large file of size f to host 2 with MSS = 2,000 bytes over a 100 Mb/s link. Knowing that the TCP sequence number field has 4 bytes, find f such that TCP sequence numbers are not exhausted. Find the time it takes to transmit f . Include the link, network, and transport headers attached to each segment.
3.	Assume that a TCP connection is established. Find the number of round-trip times the connection takes before it can transmit n segments, using Slow-start congestion control Additive increase congestion control
4.	We want to understand the fairness index of resource allocations . Suppose that a congestion-control scheme can face five possible flows with the following throughput rates: B ₁ = 1 Gb/s, B ₂ = 1 Gb/s, B ₃ = 1 Gb/s, B ₄ = 1.2 Gb/s, and B ₅ = 16 Gb/s. Calculate the fairness index for this scheme for B ₁ , B ₂ , and B ₃ . What useful information does the result of part (a) provide? Now, consider all five flows, and calculate the fairness index for this scheme. What would the result of part (c) mean to each flow?
5.	Assume that a TCP connection is established over a moderately congested link. The connection loses one packet every five segments (packets). Can the connection survive at the beginning with the linear portion of congestion avoidance ? Assume that the sender knows that the congestion remains in the network for a long time. Would it be possible for the sender to have a window size greater than five segments? Why?
6.	A TCP connection is established over a 1.2 Gb/s link with a round-trip time of 3.3 ms. To transmit a file of size 2 MB, we start sending it, using 1 K packets. How long does the transmission take if an additive increase, multiplicative decrease control with a window size of ‰ _g = 500 K is used? Repeat part (a), using slow-start control. Find the throughput of this file transfer. Find the bandwidth utilization for this transfer.
7.	Consider that an established TCP connection has a round-trip time of approximately 0.5 second and forms a window size of ‰ _g =6 K. The sending source transmits segments (packets) every 50 ms, and the destination acknowledges each segment every 50 ms. Now assume that a congestion state develops in this connection such that the destination does not receive a segment. This loss of segment is detected by the fast-retransmit method at the fourth receipt of duplicate ACK. Find the amount of time the sending source has lost if the source uses the arrival of duplicate ACKs as a sign for moving the window forward one segment. Repeat part (a), this time under a condition that the sending source waits to receive the ACK of the retransmitted packet before moving the window forward one segment.