Q1-1.The five components of a data communication system are the sender, the

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CHAPTER 1

PRACTICE SET

Questions Q1-1.The five components of a data communication system are the sender, the receiver, the transmission medium, the message, and the protocol.Q1-2.The three criteria are performance, reliability, and security.Q1-3.Advantages of a multipoint over a point-to-point configuration (type of con- nection) include ease of installation and low cost.Q1-4.Line configurations (or types of connections) are point-to-point and multi- point.

Q1-5.We can divide line configuration in two broad categories:

a.Point-to-point: mesh, star, and ring.

b.Multipoint: bus

Q1-6.In half-duplex transmission, only one entity can send at a time; in a full- duplex transmission, both entities can send at the same time.

Q1-7.We give an advantage for each of four network topologies:

a.Mesh: secure

b.Bus: easy installation

c.Star: robust

d.Ring: easy fault isolation

Q1-8.The number of cables for each type of network is:

a.Mesh: n (n − 1) / 2

b.Star: n

(Data Communications and Networking 5e Behrouz A. Forouzan) (Solution Manual all Chapters) 1 / 4

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c.Ring: n − 1

d.Bus: one backbone and n drop lines

Q1-9.The general factors are size, distances (covered by the network), structure, and ownership.Q1-10.An internet is an interconnection of networks. The Internet is the name of a specific worldwide network Q1-11.A protocol defines what is communicated, in what way and when. This pro- vides accurate and timely transfer of information between different devices on a network.Q1-12.A link-layer switch is designed not to broadcast messages. This means that it should have the link-layer address of each station to forward the packet to that particular station, not to others.Q1-13.Each LAN should be connected to (n − 1) LANs, which means that we will have n × (n − 1) connections. However, if each connection can be used in both directions, we need only [n × (n − 1)]/2 connections.Q1-14.Local telephone communication is mostly a circuit-switched network. When the communication is established, the circuit is dedicated between the two parties.Q1-15.The telephone company acts as an ISP. The connection from the resident to the telephone company is a point-to-point access WAN that connects the premises to the Internet. At the same time, the telephone company needs to provide the necessary services such as e-mail.Q1-16.To make the communication bidirectional, each layer needs to be able to pro- vide two opposite tasks, one in each direction.Q1-17.An Internet draft is a working document with no official status and a six- month lifetime; an Internet draft may become a proposed standard after six months if it has received enough attention in the Internet community.Q1-18.A required RFC is one that needs to be implemented by all Internet systems. A recommended RFC does not have to be implemented by all Internet systems; it is recommended only for its usefulness.Q1-19.The IETF is responsible for identifying operational problems and recom- mending solutions; the IRTF focuses on long-term research topics. 2 / 4

3 Problems P1-1.Unicode uses 32 bits to represent a symbol or a character. We can define 2 32 different symbols or characters.P1-2.With 16 bits, we can represent up to 2 16 different colors.P1-3.

a.Cable links: n (n – 1) / 2 = (6 × 5) / 2 = 15

b.Number of ports: (n – 1) = 5 ports needed per device

P1-4.

a.Mesh topology: If one connection fails, the other connections will still be

working.

b.Star topology: The other devices will still be able to send data through the

hub; there will be no access to the device which has the failed connection to the hub.c.Bus Topology: All transmission stops if the failure is in the bus. If the drop- line fails, only the corresponding device cannot operate.

d.Ring Topology: The failed connection may disable the whole network

unless it is a dual ring or there is a by-pass mechanism.P1-5.This is a LAN. The Ethernet hub creates a LAN as we will see in Chapter 13.P1-6.Theoretically, in a ring topology, unplugging one station, interrupts the ring.However, most ring networks use a mechanism that bypasses the station; the ring can continue its operation.P1-7.In a bus topology, no station is in the path of the signal. Unplugging a station has no effect on the operation of the rest of the network.P1-8.a.E-mail is not an interactive application. Even if it is delivered immediately, it may stay in the mail-box of the receiver for a while. It is not sensitive to delay.b.We normally do not expect a file to be copied immediately. It is not very sensitive to delay.c.Surfing the Internet is the an application very sensitive to delay. We except to get access to the site we are searching. 3 / 4

4 P1-9.In this case, the communication is only between a caller and the callee. A ded- icated line is established between them. The connection is point-to-point.P1-10.The telephone network was originally designed for voice communication; the Internet was originally designed for data communication. The two networks are similar in the fact that both are made of interconnections of small net- works. The telephone network, as we will see in future chapters, is mostly a circuit-switched network; the Internet is mostly a packet-switched network.

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