CS 455/555 - Intro to Networks and Communication
Spring 2013: Tues/Thurs 11am-12:15pm, Const 1009

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  • Dr. Michele Weigle
  • mweigle at cs.odu.edu
  • E&CS 3214
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Program 2: Ping with TCP and UDP

Assigned: Tuesday, February 19, 2013
Due: Tuesday, March 19, 2013

Description

The goal of this assignment is to help you become familiar with socket programming in Java or Python using both TCP and UDP sockets. We'll be implementing a ping-like client-server application that allows a client to measure the round-trip time (RTT) to a server.

Because we're limited to running the programs on-campus where there will be little delay and very little loss, the server will add some artificial delay and ignore some ping requests (for UDP) to simulate packet loss.

PingClient

  • The ping client will accept three command-line arguments: hostname, port, and protocol.
    • hostname - the name of the server
    • port - the port the server is running on
    Note that for ODU-CS machines, the port must be between 10001-11000. Also, these ports are only accessible to clients that are on campus.
    • protocol - either TCP or UDP (all caps)
  • As with the Program 1, if any of the arguments are incorrect, exit after printing an error message of the form ERR - arg x, where x is the argument number.
  • Depending on the protocol given, the ping client will either setup a TCP connection to send each message or send UDP datagrams. For TCP, this application-level protocol is non-persistent, meaning that there is one request-reply exchange per TCP connection.
  • The client will send 10 messages to the server in the following format:
PING seqno timestamp
where PING is the word "PING", seqno is the ping sequence number (between 0-9), and timestamp is the time (in milliseconds) that the message was created and sent
  • The client will not send a new ping until the previous ping has been answered.
  • On a single line, the client will print the message that it sends to the server and the round-trip time for the ping or a * if the reply is not received in 1 second (for UDP only).
  • After receiving the 10th reply (or after its timeout), the client will print a summary with a format similar to that displayed by the ping Unix command. Example:
---- PING Statistics ----
10 packets transmitted, 7 packets received, 30% packet loss
round-trip (ms) min/avg/max = 63/190.29/290
Print the average RTT with up to 2 digits after the decimal.

PingServer

  • The ping server is essentially an echo server (whatever data is sent will be returned).
  • The ping server will accept 2 required command-line arguments: port and protocol.
    • port - the port the server is running on
    • protocol - either TCP or UDP (all caps)
  • The ping server will accept 1 optional command-line argument: seed.
    • seed - a long to seed the random number generator for generating delays and lost packets
  • As with the Program 1, if any of the arguments are incorrect, exit after printing an error message of the form ERR - arg x, where x is the argument number.
  • After a ping request has been received by the UDP server, the server will determine if it should ignore the packet or respond to it (simulating losses). Default loss rate is 25%.
  • If the ping will be responded to (i.e., it is not dropped), the server will first wait for a random amount of time to simulate network delay (average 150 ms each way).
  • On a single line, the server will print the IP address and port of the client, the client's ping message, and the server's action.
The server's action will either be "not sent" if the ping was ignored or "delayed x ms" .
  • The ping server will keep running until the user presses Ctrl-C.
For TCP, the server will close the client connection after each ping reply is sent.

Rules

  • As with all projects, you are not permitted to work with anyone else (even students not in the class) - all of the coding and documentation must be your own.
  • Your programs must compile and run on the CS Unix machines.
  • You must write neat code and document it well. You will lose points for sloppy programs that contain little or no comments.

Testing

A large part of your program's grade will be determined by how well it handles a set of inputs. You should test your program rigorously before submitting. Because your programs will be run and tested using a script, you must format your output exactly as I have described or you will lose points.

Since Java and Python use different random number generators, they will produce different results with the same seed. So, I'm providing separate examples for each language.

Java Examples

Example 1

java PingClient
Usage: java PingClient hostname port protocol
       protocol - {TCP, UDP}

java PingServer
Usage: java PingServer port protocol [seed]
       protocol - {TCP, UDP}

Example 2

java PingClient atria three TCP
ERR - arg 2

java PingServer 10002 tcp
ERR - arg 2

Example 3

atria> java PingServer 10002 TCP 123
128.82.4.244:33968> PING 0 1360792272731  ACTION: delayed 216 ms
128.82.4.244:33969> PING 1 1360792272949  ACTION: delayed 297 ms
128.82.4.244:33970> PING 2 1360792273248  ACTION: delayed 75 ms
128.82.4.244:33971> PING 3 1360792273324  ACTION: delayed 182 ms
128.82.4.244:33972> PING 4 1360792273508  ACTION: delayed 241 ms
128.82.4.244:33973> PING 5 1360792273751  ACTION: delayed 262 ms
128.82.4.244:33974> PING 6 1360792274014  ACTION: delayed 214 ms
128.82.4.244:33975> PING 7 1360792274230  ACTION: delayed 21 ms
128.82.4.244:33976> PING 8 1360792274252  ACTION: delayed 238 ms
128.82.4.244:33977> PING 9 1360792274492  ACTION: delayed 173 ms

sirius>  java PingClient atria 10002 TCP 
PING 0 1360792272731  RTT: 217 ms
PING 1 1360792272949  RTT: 298 ms
PING 2 1360792273248  RTT: 76 ms
PING 3 1360792273324  RTT: 183 ms
PING 4 1360792273508  RTT: 242 ms
PING 5 1360792273751  RTT: 263 ms
PING 6 1360792274014  RTT: 215 ms
PING 7 1360792274230  RTT: 22 ms
PING 8 1360792274252  RTT: 239 ms
PING 9 1360792274492  RTT: 174 ms
---- PING Statistics ----
10 packets transmitted, 10 packets received, 0% packet loss
round-trip (ms) min/avg/max = 22/192.9/298

Notes:

  • The delays the server uses should be the same with the same seed, but the timestamps in the client's ping message will not since they depend on the time the program was run.
  • With TCP since you are creating a new connection for each PING sent, the client's port number will be different each time.
  • The RTTs that the client reports should be similar to the example, but may not be exact.

Example 3

atria> java PingServer 10002 UDP 123
128.82.4.244:44229> PING 0 1360792326564  ACTION: delayed 297 ms
128.82.4.244:44229> PING 1 1360792326863  ACTION: delayed 182 ms
128.82.4.244:44229> PING 2 1360792327046  ACTION: delayed 262 ms
128.82.4.244:44229> PING 3 1360792327309  ACTION: delayed 21 ms
128.82.4.244:44229> PING 4 1360792327331  ACTION: delayed 173 ms
128.82.4.244:44229> PING 5 1360792327505  ACTION: delayed 44 ms
128.82.4.244:44229> PING 6 1360792327550  ACTION: delayed 19 ms
128.82.4.244:44229> PING 7 1360792327570  ACTION: not sent
128.82.4.244:44229> PING 8 1360792328571  ACTION: not sent
128.82.4.244:44229> PING 9 1360792329573  ACTION: delayed 262 ms

sirius> java PingClient atria 10002 UDP
PING 0 1360792326564  RTT: 299 ms
PING 1 1360792326863  RTT: 183 ms
PING 2 1360792327046  RTT: 263 ms
PING 3 1360792327309  RTT: 22 ms
PING 4 1360792327331  RTT: 174 ms
PING 5 1360792327505  RTT: 45 ms
PING 6 1360792327550  RTT: 20 ms
PING 7 1360792327570  RTT: *
PING 8 1360792328571  RTT: *
PING 9 1360792329573  RTT: 263 ms
---- PING Statistics ----
10 packets transmitted, 8 packets received, 20% packet loss
round-trip (ms) min/avg/max = 20/158.62/299

Python Examples

Example 1

python PingClient.py
Usage: python PingClient.py hostname port protocol
       protocol - {TCP, UDP}

python PingServer.py
Usage: python PingServer.py port protocol [seed]
       protocol - {TCP, UDP}

Example 2

python PingClient.py atria three TCP
ERR - arg 2

python PingServer.py 10002 tcp
ERR - arg 2

Example 3

atria> python PingServer.py 10002 TCP 123
128.82.4.244:34747> PING 0 1361211379146  ACTION: delayed 15 ms
128.82.4.244:34748> PING 1 1361211379163  ACTION: delayed 26 ms
128.82.4.244:34749> PING 2 1361211379190  ACTION: delayed 122 ms
128.82.4.244:34750> PING 3 1361211379314  ACTION: delayed 32 ms
128.82.4.244:34751> PING 4 1361211379348  ACTION: delayed 270 ms
128.82.4.244:34752> PING 5 1361211379619  ACTION: delayed 11 ms
128.82.4.244:34753> PING 6 1361211379632  ACTION: delayed 160 ms
128.82.4.244:34754> PING 7 1361211379794  ACTION: delayed 99 ms
128.82.4.244:34755> PING 8 1361211379894  ACTION: delayed 255 ms
128.82.4.244:34756> PING 9 1361211380151  ACTION: delayed 47 ms

sirius>  python PingClient.py atria 10002 TCP 
PING 0 1361211379146 RTT: 16 ms
PING 1 1361211379163 RTT: 26 ms
PING 2 1361211379190 RTT: 123 ms
PING 3 1361211379314 RTT: 33 ms
PING 4 1361211379348 RTT: 271 ms
PING 5 1361211379619 RTT: 12 ms
PING 6 1361211379632 RTT: 161 ms
PING 7 1361211379794 RTT: 99 ms
PING 8 1361211379894 RTT: 256 ms
PING 9 1361211380151 RTT: 48 ms
---- PING Statistics ----
10 packets transmitted, 10 packets received, 0.0% packet loss
round-trip (ms) min/avg/max = 12/104.50/271

Notes:

  • The delays the server uses should be the same with the same seed, but the timestamps in the client's ping message will not since they depend on the time the program was run.
  • With TCP since you are creating a new connection for each PING sent, the client's port number will be different each time.
  • The RTTs that the client reports should be similar to the example, but may not be exact.

Example 3 - edited 3/5/13 -MCW

atria> python PingServer.py 10002 UDP 123
128.82.4.244:58353> PING 0 1361211436430  ACTION: not sent
128.82.4.244:58353> PING 1 1361211437433  ACTION: not sent
128.82.4.244:58353> PING 2 1361211438435  ACTION: delayed 32 ms
128.82.4.244:58353> PING 3 1361211438468  ACTION: delayed 11 ms
128.82.4.244:58353> PING 4 1361211438480  ACTION: delayed 99 ms
128.82.4.244:58353> PING 5 1361211438580  ACTION: delayed 47 ms
128.82.4.244:58353> PING 6 1361211438628  ACTION: delayed 100 ms
128.82.4.244:58353> PING 7 1361211438729  ACTION: not sent
128.82.4.244:58353> PING 8 1361211439731  ACTION: not sent
128.82.4.244:58353> PING 9 1361211440733  ACTION: delayed 26 ms

sirius> python PingClient.py atria 10002 UDP
PING 0 1361211436430 RTT: *
PING 1 1361211437433 RTT: *
PING 2 1361211438435 RTT: 33 ms
PING 3 1361211438468 RTT: 12 ms
PING 4 1361211438480 RTT: 100 ms
PING 5 1361211438580 RTT: 48 ms
PING 6 1361211438628 RTT: 101 ms
PING 7 1361211438729 RTT: *
PING 8 1361211439731 RTT: *
PING 9 1361211440733 RTT: 27 ms
---- PING Statistics ----
10 packets transmitted, 6 packets received, 40.0% packet loss
round-trip (ms) min/avg/max = 12/53.50/101

Notes/FAQs

  • Where can I find information about Java classes?
  • Where can I find information about Python functions?
  • Can I use the linux.cs.odu.edu alias when running these programs?
No. You must use an actual machine name (atria or sirius). Think about why.
  • How can I get the current time in milliseconds?
Java: See System.currentTimeMillis()
Python: See time.time()
  • How can I set a timeout value on reading from a datagram socket?
Java: See the setSoTimeout() function in the DatagramSocket class.
Python: See the settimeout() function in the socket library.
  • How can I format a double to have a certain number of digits after the decimal?
Java: See the DecimalFormat class.
Python: See the str.format() function.
  • How can I generate a random loss pattern and artificial delay?
Java:
  • Use the java.util.Random class (so put import java.util.* at the beginning of your program).
  • Between your class PingServer { and public static void main lines, insert:
private static final double LOSS_RATE = 0.25;
private static final int AVERAGE_DELAY = 150; // milliseconds
  • To set the random number generator seed and create the Random object (after you have determined if the user has given you a seed argument), use
// Create random number generator for use in simulating packet loss and network delay.
Random random;
if (seed == 0) {
    random = new Random();
} else {
    random = new Random(seed);
}
Note: The Random object should be created only once in the server program. Do not create new Random objects for each connection or for each packet received.
  • To determine whether to reply to a ping, use
// Decide whether to reply, or simulate packet loss.
if (random.nextDouble() < LOSS_RATE) 
If this evaluates to true, print 'not sent' and don't send the reply.
If this evaluates to false, send the reply.
  • To add delay, use
// Simulate network delay.
delay = (int) (random.nextDouble() * 2 * AVERAGE_DELAY);
Thread.sleep(delay);
Don't forget to print out the delay amount.
Python:
  • Use random (so put import random at the beginning of your program).
  • Create the following global constants:
LOSS_RATE = 0.25
AVERAGE_DELAY = 150 # milliseconds
  • To set the random number generator seed (after you have determined if the user has given you a seed argument):
# Create random number generator for use in simulating packet loss and network delay.
random.seed(seed)
Notes:
  • If seed == 0, the seed will be set based on the current time of day. This will produce different values each time you run the program.
  • random.seed() should be called only once in the server program. Do not reset the seed for each connection or for each packet received.
  • To determine whether to reply to a ping, use
# Decide whether to reply, or simulate packet loss.
if random.random() < LOSS_RATE 
If this evaluates to true, print 'not sent' and don't send the reply.
If this evaluates to false, send the reply.
  • To add delay, use
# Simulate network delay.
delay = (random.random() * 2 * AVERAGE_DELAY) # sleep time in ms
time.sleep(delay/1000.0) # accepts time in secs 
Don't forget to print out the delay amount.

Submission

You must name your source files PingClient.java and PingServer.java (note the capitalization) or PingClient.py and PingServer.py. Make sure that you submit all files necessary to compile your program. But, do not submit compiled files (.class files).

Directions for submitting your assignment through Blackboard