Chapter 1 - Problems

For each of the following four networks, discuss the consequences if a connection fails. a. Five devices arranged in a mesh topology b. Five devices arranged in a star topology (not counting the hub) c. Five devices arranged in a bus topology d. Five devices arranged in a ring topology

1. Mesh topology: If one connection fails, the other connections will still be working. 2. 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. 3. Bus Topology: All transmission stops if the failure is in the bus. If the drop-line fails, only the corresponding device cannot operate. 4. Ring Topology: The failed connection may disable the whole network unless it is a dual ring or there is a by-pass mechanism.

A television broadcast is an example of _______ transmission. A) simplex B) half-duplex C) full-duplex D) automatic

A

Frequency of failure and network recovery time after a failure are measures of the _______ of a network.A) ReliabilityB) PerformanceC) SecurityD) Feasibility

A

In a ________ connection, three or more devices share a link. A) multipoint B) point-to-point C) (a) and (b) D) none of the above

A

An unauthorized user is a network _______ issue. A) Reliability B) Performance C) Security D) All the above

C

Assume six devices are arranged in a mesh topology. How many cables are needed? How many ports are needed for each device?

Cable links: n (n - 1) / 2 = (6 × 5) / 2 = 15 Number of ports: (n - 1) = 5 ports needed per device

In the bus topology in Figure 1.6, what happens if one of the stations is unplugged?

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.

When a party makes a local telephone call to another party, is this a point-to-point or multipoint connection? Explain the answer.

In this case, the communication is only between a caller and the callee. A dedicated line is established between them. The connection is point-to-point.

Compare the telephone network and the Internet. What are the similarities? What are the differences?

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 networks. The telephone network, as we will see in future chapters, is mostly a circuit-switched network; the Internet is mostly a packet-switched network.

In the ring topology in Figure 1.7, what happens if one of the stations is unplugged?

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.

We have two computers connected by an Ethernet hub at home. Is this a LAN or a WAN? Explain the reason.

This is a LAN. The Ethernet hub creates a LAN.

What is the maximum number of characters or symbols that can be represented by Unicode?

Unicode uses 32 bits to represent a symbol or a character. We can define 2^32 different symbols or characters.

A color image uses 16 bits to represent a pixel. What is the maximum number of different colors that can be represented?

With 16 bits, we can represent up to 2^16 different colors.

Performance is inversely related to delay. When we use the Internet, which of the following applications are more sensitive to delay? a. Sending an e-mail b. Copying a file c. Surfing the Internet

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.