Chapter 7, Problem 1MC

Program Plan Intro

Problem in designing a new Ethernet:

• It is given that there is a problem on designing a new Ethernet, because if one computer transmits a frame but on other side, the other computer does not know about the incoming frame from the first then it results in collision or the frame will be lost. To avoid this situation, it is need to ensure about the length of the cable in the Local Area Network (LAN).
• The LAN cable must be smaller than the frame which is sent over the network. If it is not smaller, then the collision problem cannot be detected.

Explanation of Solution

b.

Given data:

It is given that the smallest possible message is 64 bytes and it uses 10GbE. It is need to calculate the number of meters or feet that the 64byte message travels over the network.

• Moreover, it is given that the electricity passing through the cable is slower than the speed of light. So, based on the given assumption, let the speed of light is takes as 186,000 miles per second.

Number of miles that the 64byte message travels:

To calculate the number of miles that the 64byte message travels on network, let need to do following steps,

• Initially convert the length of message into bits or bytes. So,

  $\begin{array}{c}\text{Length of the message = 64 }\times \text{8 (bytes to bits)}\\ \text{=512 bits}\end{array}$

• Now, divide the length of message by the speed of the cable to calculate the number of seconds that the message is transmitted. Note 1 million is equal to 1,000,000.

  $\begin{array}{c}\left\{\begin{array}{l}\text{Number}\text{of}\text{seconds}\text{for}\\ \text{message}\text{transmission}\end{array}\right\}\text{= }\end{array}$

Explanation of Solution

c.

Given data:

It is given that the answer for part (b) covers the maximum distance can be covered by the single cable run from a switch to computer in Ethernet. For this problem, there is a need to find the solution.

Recommended solution:

The message which is travelled must be longer than the cable connecting two devices. If it is not longer, then it leads to collision in the middle of the cable and neither of the two devices connected in a cable would detect the collision.

• With 10 Base-T networks, the message is longer than any cable so there is no problem but in 10GbE, cables are not longer than 15 meters if the messages are short as 64 bytes...