Chapter 1 - Questions

Categorize the four basic topologies in terms of line configuration.

1. Mesh (every device connected by point to point) 2. Bus (multipoint connection where one cable links all devices using droplines and taps) 3. Star (each device connected by point to point to a central hub, not to each other) 4. Ring (each device connected by point to point with the two devices on either side; repeaters regenerate bits to pass data along)

For n devices in a network, what is the number of cable links required for a mesh, ring, bus, and star topology?

1. Mesh: n (n - 1) / 2 2. Star: n 3. Ring: n 4. Bus: n+1

Name the four basic network topologies, and cite an advantage of each type.

1. Mesh: secure 2. Bus: easy installation 3. Star: robust 4. Ring: easy fault isolation

Why are protocols needed?

A protocol defines what is communicated, in what way and when. This provides accurate and timely transfer of information between different devices on a network.

What are the advantages of a multipoint connection over a point-to-point one?

ease of installation and low cost

What are the three criteria necessary for an effective and efficient network?

performance, reliability, and security

What are the two types of line configuration?

point to point and multipoint

Identify the five components of a data communications system

sender, receiver, transmission medium, message, and protocol

What are some of the factors that determine whether a communication system is a LAN or WAN?

size, distances (covered by the network), structure, and ownership

Explain the difference between an Internet draft and a proposed standard.

An Internet draft is a working document with no official status and a six-month lifetime.A proposed standard is a specification that is stable, well understood, and of sufficient interest to the Internet community. At this level, the specification is usually tested and implemented by several different groups.

What is an internet? What is the Internet?

An internet is an interconnection of networks. The Internet is the name of a specific worldwide network

When we use local telephones to talk to a friend, are we using a circuit-switched network or a packet-switched network?

Circuit switched

How many point-to-point WANs are needed to connect n LANs if each LAN should be able to directly communicate with any other LAN?

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.

What is the difference between half-duplex and full-duplex transmission modes?

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

In a LAN with a link-layer switch (Figure 1.8b), Host 1 wants to send a message to Host 3. Since communication is through the link-layer switch, does the switch need to have an address? Explain.

No. You do not need an ip address to transmit data to devices connected by a switch (layer 2); you only need the mac address. Switches accessed remotely through the network must have a layer 3 (ip) address.

Explain the difference between a required RFC and a recommended RFC.

Required. An RFC is labeled required if it must be implemented by all Internet systems to achieve minimum conformance. For example, IP and ICMP (Chapter 19)are required protocols.An RFC labeled recommended is not required for minimum conformance; it is recommended because of its usefulness. For example, FTP(Chapter 26) and TELNET (Chapter 26) are recommended protocols.

Explain the difference between the duties of the IETF and IRTF.

The IETF is responsible for identifying operational problems and recommending solutions; the IRTF focuses on long-term research topics.

What is the first principle we discussed in this chapter for protocol layering that needs to be followed to make the communication bidirectional?

The first principle dictates that if we want bidirectional communication, we need to make each layer so that it is able to perform two opposite tasks, one in each direction.

When a resident uses a dial-up or DLS service to connect to the Internet, what is the role of the telephone company?

The telephone company acts as an ISP. The connection from the resident tothe telephone company is a point-to-point access WAN that connects thepremises to the Internet. At the same time, the telephone company needs toprovide the necessary services such as e-mail.