Chapter 7

Show how a modem would encode the 5-bit binary sequence 11001 onto an analog carrier by a. Modifying its amplitude (the height of the carrier wave) b. Modifying its frequency (the number of waves per second)

Explain why noise and interference have a more serious impact on an analog transmission line (like a telephone link) than on a digital transmission line.

Determine the total time it takes to transmit an uncompressed grayscale image (with 8 bits/pixel) from a screen with a resolution of $1,280\times 840$ pixels using each of the following media: a. A $56\mathrm{Kbps}$ modem b. A $1.5$ Mbps DSL line c. A $100\mathrm{Mbps}$ Ethernet link

Assume that we need to transmit a $1,440\times$ 900 uncompressed color image (using 16 bits per pixel) over a computer network in less than $0.01$ second. What is the minimal necessary line speed to meet this goal?

Why is an address field needed in the Ethernet LAN protocol? Can you think of a useful situation in which you might want either to omit the address field entirely or to use some "special" address value in the address field?

The Ethernet is a distributed LAN protocol, which means that there is no centralized control node and that the failure of a single node can never bring down the entire network. However, can you think of any advantage to the creation of a centralized LAN in which one node is in charge of the entire network and makes all decisions about who can send a message and who must wait? Explain.

Agree or disagree with the following assertion and state why: In an Ethernet network, even though there are collisions, every message is guaranteed to be delivered in some maximum amount of time $T$.

In Exercise 11, you determined the minimum number of links needed to ensure that every one of the $N$ nodes in a network can communicate with every other node. However, most networks have far more than this minimum. What are the advantages of having these "extra" links in the network?

What are the advantages of breaking up a single logical message into a number of fixed-sized packets and then sending each one of those packets independently through the network?