For all the experiments, you will be using a network island. It is composed of two terminals on the xinu network and two laptop computers, which will be provided in the lab. These four computers are connected through the hub. The xinu terminals are connected to the outside world but the laptops are not. They are connected only to the xinu terminals, which are not configured to act as routers.
 

Purpose Of The Exercise

In this exercise, students will become familiar with a measuring device known as a Time Domain Reflectometer (TDR) that can be used to detect a broken cable.
 

Overview

A TDR attaches to one end of a copper cable, and measures the length of the cable. It does so by  transmitting electrical pulses of a suitable shape. Irregularities in the cable cause "reflections" of the electrical signals, which are received back at the TDR. In particular, the (unterminated) end of a broken wire always causes electrical signals to reflect in the same way a mirror reflects light.

A TDR contains an accurate timer which it uses to measure the difference in time between the original transmission and the reflection. From the time and the speed of propagation, it computes the length of the wire (i.e., distance to the fault).
 

Procedure And Details

To see a TDR in action, you will be provided with a TDR and some cables. You will use the TDR to measure the length and related properties of the provided cables. Record the various measurements on paper. Note: some cables may be damaged, others fine. Submit a 1/3-page write-up of what experiments you carried, the measurements you observed/recorded, and your commentary/interpretation of the measurements.
 

Ping (15 pts):

The Ping (Packet Internet Groper) program is used to query another system and ensure a connection is active as well as determine the completion time (the query packet to reach its destination plus the response packet to arrive). It operates by sending a request to the destination machine for a reply. If the destination's IP software receives the request it issues a reply immediately. If ping is unable to reach the destination machine an error message will be shown.

Run ping as

$> ping -s local-machine 1024 20

where local-machine is the hostname or IP address of another local machine in the lab. The "-s" flag specifies that packets be emitted once every second, "1024" specified the size of the packet (in bytes), and "20" specifies the number of packets that should be emitted. Record the terminal output using script. Rerun the experiment with packet sizes "2048", "4096", and "8192". Use gnuplot to plot the average round-trip time (RTT), minimum RTT, and maximum RTT (on the y-axis) against packet size (on the x-axis). Do you observe a trend? Discuss your observations in a 1/2-page write-up (excluding the two figures).

Rerun the previous experiments with host csa.bu.edu in place of a local machine in the lab.
 

Ifconfig (5 pts):

Ifconfig is used for configuration of network interfaces, but we will use it only to discover the IP address of the machines on the network. To do this, you will use ifconfig with the -a option as follows :

$> ifconfig -a

This command gives details of all the network interfaces on the machine. Use script to store the output and hand it in along with the other material.
 

Traceroute (10 pts):

This utility tracks the route that a packet from your machine follows, over the Internet, to the destination machine.

It gives you the number of hops that your packet goes through and also displays their corresponding IP address.

Run traceroute as

$> traceroute local-machine

Rerun traceroute with csa.bu.edu in place of local-machine. Use script to record the output. How many IP hops does it take for the packet to make it to its destination? Can you guess who these routers belong to and where they might be located? Give a 1/3-page discussion.