COMPUTER NETWORKS
CONE Lab - Computer Networks and Internet - Numerical exercises
Problem 2 (Ch. 1 of Computer Networking by J.F. Kurose and K.W. Ross)
Consider an application which transmits data at a steady rate (e.g., the sender generates a N bit unit of data every k time units, where k is small and fixed). Also, when such an application starts, it will stay on for relatively long period of time. Answer the following questions, briefly justifying your answer:
a) Would a packet-switched network or a circuit-switched network be more appropriate for this application? Why?
b) Suppose that a packet-switching network is used and the only traffic in this network comes from such applications as described above. Furthermore, assume that the sum of the application data rates is less that the capacities of each and every link. Is some form of congestion control needed? Why?
Problem 5 (Ch. 1 of Computer Networking by J.F. Kurose and K.W. Ross)
Consider sending a file of F = M * L bits over a path of Q links. Each link transmits at R bps. The network is lightly loaded so that there are no queueing delays. When a form of packet switching is used, the M * L bits are broken up into M packets, each packet with L bits. Propagation delay is negligible.
a) Suppose the network is a packet-switched virtual-circuit network. Denote the VC set-up time by ts seconds. Suppose to each packet the sending layers add a total of h bits of header. How long does it take to send the file from source to destination?
b) Suppose the network is a packet-switched datagram network, and a connectionless service is used. Now suppose each packet has 2h bits of header. How long does it take to send the file?c) Repeat (b), but assume message switching is used (i.e., 2h bits are added to the message, and the message is not segmented).
d) Finally, suppose that the network is a circuit switched network. Further suppose that the transmission rate of the circuit between source and destination is R bps. Assuming ts set-up time and h bits of header appended to the entire file, how long does it take to send the file?
Problem 7 (Ch. 1 of Computer Networking by J.F. Kurose and K.W. Ross)
This elementary problem explores propagation delay and transmission delay, two central concepts in data networking. Consider two hosts, Hosts A and B, connected by a single link of rate R bps. Suppose that the two hosts are separted by m meters, and suppose the propagation speed along the link is s meters/sec. Host A is to send a packet of size L bits to Host B.
a) Express the propagation delay, dprop in terms of m and s.
b) Determine the transmission time of the packet, dtrans in terms of L and R.
c) Ignoring processing and queing delays, obtain an expression for the end-to-end delay.
d) Suppose Host A begins to transmit the packet at time t=0. At time t=dtrans, where is the last bit of the packet?
e) Suppose dprop is greater than dtrans . At time t=dtrans, where is the first bit of the packet?
f)) Suppose dprop is less than dtrans . At time t=dtrans, where is the first bit of the packet?
g) Suppose s=2.5*108, L=100 bits and R=28 kbps. Find the distance m so that dprop equals dtrans.
Problem
A
One
host (named X) sends two packets to another host (named Y) through router
S1. Assume there is no queuing delay and processing delay. The bandwidth
and propagation delay of link 1 are 25 Kbps and 0.1 ms respectively. The
corresponding values for link 2 are 10 Kbps and 0.1 ms.
The first packet is of size 10 Kb, and the second one of size 5 Kb. Draw
the time-line diagrams illustrating these transmissions in the following
2 cases:
Diagram for problem A
(a) the second packet is sent 2 secs after the first one is sent (to be precise, the transmission of the second packet begins 2 secs after the transmission of the first one)
(b) the second packet is sent 1 sec after the first one is sent (the transmission of the second packet begins 1 sec after the transmission of the first one)
Problem
B
When
using virtual-circuit transport, the virtual-circuit setup time is 400ms.
Packets travel over a path that goes through 10 links and each link is
a 56 kbps line. Each packet contains a 7-byte header and 400 bits of data.
When using a datagram transport, each packet contains a 12-byte header
and 400-bit data. However, there is no circuit setup delay. In the following
parts, ignore the processing delay, propagation delay and queuing delay.
(a) How long does it take to transmit N packets using virtual-circuit transport?
(b) How long does it take to transmit N packets using datagram transport?
(c) For what values of N is the transfer by virtual-circuit transport faster? For what value of N is datagram transport faster?
Problem
C
Suppose a 100-Mbps point-to-point link is being
set up between the earth and a new lunar colony. The distance from the
moon to the earth is approximately 385000km, and data travels over the
link at the speed of light (3 x 108 m/s). The transmission
is reliable and window-based.
(a) Calculate the minimum Round Trip Time (RTT) for the link.
(b) Using the RTT as the delay, calculate the delay x bandwidth product for this link.
(c) What is the maximum number of bits that can be in transit at any one point?
(d) A camera on the lunar base takes pictures of the earth and saves them in digital format to disk. Suppose Mission Control on earth wishes to download the most current image, which is 25MB. What is the minimum amount of time that will elapse between when the request for the data goes out and the transfer is finished?