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Communication Network 08/09
EKT331/4
TUTORIAL 1
Chapter 1
1a. Describe the step-by-step procedure that is involved from the time you deposit a letter
in a mailbox to the time the letter is delivered to its destination. What role do names,
addresses and mail codes play? How might the letter be routed to its destination? To what
extent can the process be automated?
1b. Repeat part (a) for an e-mail message. At this point, you may have to conjecture
different approaches about what goes on inside the computer network.
1c. Are the procedures in parts (a) and (b) connection-oriented or connectionless?
2a. Describe what step-by-step procedure might be involved inside the network in
making a telephone connection.
2b. Now consider a personal communication service that provides a user with a personal
telephone number. When the number is dialed, the network establishes a connection to
wherever the user is located at the given time. What functions must the network now
perform in order to implement this service?
3. Suppose that the letter in problem 1 is sent by fax. Is this mode of communications
connectionless or connection-oriented? Real-time or non-real time?
4. Discuss the advantages and disadvantages of transmitting fax messages over the
Internet instead of the telephone network.
5. Two musicians located in different cities wish to have a jam session over a
communications network. Find the maximum possible distance between the musicians if
they are to interact in real-time, in the sense of experiencing the same delay in hearing
each other as if they were 10 meters apart. The speed of sound is approximately 330
meters/second. Assume that the network transmits the sound at the speed of light in cable,
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2.3 x 10 meters/second.
6. The propagation delay is the time that is required for the energy of a signal to
propagate from one point to another.
a. Find the propagation delay for a signal traversing the following networks at the speed
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of light in cable (2.3 x 10 meters/second):
• a circuit board 10 cm
• a room 10 m
• a building 100 m
• a metropolitan area 100 km
• a continent 5000 km
• up and down to a geostationary satellite 2 x 36000 km
Tutorial #1
Pn. Shahadah Ahmad
Communication Network 08/09
EKT331/4
7. How many bits are in transit during the propagation delay in the above cases, if bits
are entering the above networks at the following transmission speeds: 10,000 bits/second;
1 megabit/second; 100 megabits/second; 10 gigabits/second.
Chapter 2
8. (a) What universal set of communication services is provided by TCP/IP?
(b) How is independence from underlying network technologies achieved?
(c) What economies of scale result from (a) and (b)?
9. What difference does it make to the network layer if the underlying data link layer
provides a connection-oriented service versus a connectionless service?
10. Which OSI layer is responsible for the following?
(a) Determining the best path to route packets.
(b) Providing end-to-end communications with reliable service.
(c) Providing node-to-node communications with reliable service.
11. Give two features that the data link layer and transport layer have in common. Give
two features in which they differ. Hint: Compare what can go wrong to the PDUs that are
handled by these layers.
12. Suppose an application layer entity wants to send an L-byte message to its peer
process, using an existing TCP connection. The TCP segment consists of the message
plus 20 bytes of header. The segment is encapsulated into an IP packet that has an
additional 20 bytes of header. The IP packet in turn goes inside an Ethernet frame that
has 18 bytes of header and trailer. What percentage of the transmitted bits in the physical
layer correspond to message information, if L = 100 bytes, 500 bytes, 1000 bytes?
13. Suppose that the TCP entity receives a 1.5 megabyte file from the application layer
and that the IP layer is willing to carry blocks of maximum size 1500 bytes. Calculate the
amount of overhead incurred from segmenting the file into packet-sized units.
14. How does the network layer in a connection-oriented packet-switching network differ
from the network layer in a connectionless packet-switching network?
15. Consider an internetwork architecture that is defined using gateways/routers to
communicate across networks but that uses a connection-oriented approach to packet
switching. What functionality is required in the routers? Are there any additional
constraints imposed on the underlying networks?
Tutorial #1
Pn. Shahadah Ahmad