CS 779/879
Design of Network Protocols
Spring 2004
Final Exam
Time 2 & 1/2 hours
Open Book & Notes

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In achieving concurrency, we may use one of the following three techniques:

1. Fork

2. Thread

3. Select

In the following two problems use any technique at most once to solve the concurrency problem.

Q1: [40 points]

Write a tcp-based program C that allows two persons A and B to chat with each other. The syntax of using C is:

% C <host>

Where <host> is an IP address of the other person.

For example, person A types:

% C <ip-address-of-host B>

While person B types:

% C <ip-address-of-host A>

C creates a tcp socket t, connects it to <host> at port 4444. If the connection is not established within 4 seconds, it waits for a connection from <host> and port 4444. Any connection that comes from a different host or a different port should be rejected.

When the connection is established, C displays the message:

“Please type any thing followed by return. To exit type ctrl-D”

The program then concurrently:

1. Reads any message from the keyboard and the sends it to t

2. Receives any message from t and displays it to the TTY.

Q2: [40 points]

In the following we would like to develop a udp tunnel to allow two different groups (e.g., one at ODU the other at UNC) to chat using multicast as shown below:

CcC

ODU

UNC

T

T

C

C

C

C

C

C

udp socket

Mcast socket

C Chat ClientClient

T Server

udp tunnel

Write the code for T. The syntax of using T is:

% T <host>

Where <host> is the IP address of the other end of the tunnel.

T creates two sockets:

1. A udp socket u connected to <host> and port 2222.

2. A multicast socket m that joins the multicast group “224.1.1.1/4444”.

T then concurrently:

1. sends any message received from u to m.

2. sends any message received from m to u.

Make sure to set the “loopback” of m appropriately.

Q3: [20 points]

A.

In Q2, what is the effect of changing the multicast port from 4444 to 2222?

B.

In Q2, what is the meaning of the sentence?

Make sure to set the “loopback” of m appropriately

C.

In SCTP, what is the corresponding concept to the TCP’s KEEPALIVE?

D.

How to express an IP4 address (e.g., 128.82.4.8) as an IP6 address?