Program 4: Alternating Bit Reliable Transport

Assigned: Tuesday, November 10, 2009
Due: Tuesday, November 24, 2009 before class

Note: I have changed the examples to match the description of the program. Previously, telling the sender to send 5 messages would have sent messages with data 0-5 (6 messages). Your program (and the new examples) should have the correct behavior of sending messages with data 0-4 (5 messages). -MCW 11/25 @ 9:30am

NOTE: Program 4 is required for CS 555 only. CS 455 students can complete this program for extra-credit. To receive extra-credit, the program must work completely.

Description

The goal of this assignment is to implement the alternating bit reliable transport protocol that you designed in your last homework assignment. You will implement both a sender and a receiver.

Sender

• The sender accepts three command-line arguments: receiver hostname, receiver port, number of unique messages to send
• The sender sends messages with the following format: SEQNO DATA MSGS
  • SEQNO starts at 0
  • DATA starts at 0 and increases by 1
  • MSGS is the total number of unique messages that will be sent
• Since this is an alternating bit protocol, the sender cannot send the next message until the previous one has been acknowledged by the receiver.
• If an ACK is not received before the timer expires, the previous message must be re-sent.
  • Set the timeout to 1 second (1000 ms).
• The sender program should exit when the ACK for the last message has been received.

Receiver

• The receiver accepts three required command-line arguments: listening port, average delay, and loss percentage. The receiver also accepts an optional fourth command-line argument: seed.
• Each time the receiver gets a message from the sender, it will respond with an ACK.
• Before sending an ACK, the server will delay or drop the packet as in Program 2.
  • The ACK for the last message should not be dropped.
  • To get loss and delay like the examples, make sure that you only create the Random object once, decide if the packet should be dropped first, and only choose delays for packets that will not be dropped.
• The receiver should determine the number of unique messages that will be sent by looking at the first message sent by the sender.
• The receiver will print the data of each message received from the sender. See the testing section for examples. As done previously, your program will be tested using a script, so make sure that your output matches the examples exactly.
• The receiver program should exit when it has sent the ACK for the last message.

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.

Example 1

antares> java AbrtReceiver
Usage: java AbrtReceiver port delay lossRate [seed]
         port - listening port (10001-11000)
         delay - avg delay (ms)
         lossRate - loss percentage [0-1]
         seed - RNG seed (optional)

vega> java AbrtSender 
Usage: java AbrtSender host port msgs
         host - receiver hostname
         port - receiver port (10001-11000)
         msgs - number of unique messages to send

Example 2

antares> java AbrtReceiver 10005 4 40
ERR - arg 3

Example 3

antares>   java AbrtReceiver 10005 500 0.1 7777
RECV: 0 0 4
SENT: ACK 0 - delayed 425 ms

RECV: 1 1 4
SENT: ACK 1 - not sent

RECV: 1 1 4
SENT: ACK 1 - delayed 577 ms

RECV: 0 2 4
SENT: ACK 0 - delayed 701 ms

RECV: 1 3 4
SENT: ACK 1 - delayed 872 ms

vega>  java AbrtSender antares 10005 4
SENT: 0 0 4
RECV: ACK 0

SENT: 1 1 4 - timeout

SENT: 1 1 4
RECV: ACK 1

SENT: 0 2 4
RECV: ACK 0

SENT: 1 3 4
RECV: ACK 1

Example 4

antares> java AbrtReceiver 10005 150 0.2 7890
RECV: 0 0 4
SENT: ACK 0 - not sent

RECV: 0 0 4
SENT: ACK 0 - not sent

RECV: 0 0 4
SENT: ACK 0 - delayed 197 ms

RECV: 1 1 4
SENT: ACK 1 - delayed 131 ms

RECV: 0 2 4
SENT: ACK 0 - not sent

RECV: 0 2 4
SENT: ACK 0 - delayed 270 ms

RECV: 1 3 4
SENT: ACK 1 - delayed 145 ms

vega> java AbrtSender antares 10005 4
SENT: 0 0 4 - timeout

SENT: 0 0 4 - timeout

SENT: 0 0 4
RECV: ACK 0

SENT: 1 1 4
RECV: ACK 1

SENT: 0 2 4 - timeout

SENT: 0 2 4
RECV: ACK 0

SENT: 1 3 4
RECV: ACK 1

Example 5

I'm not giving the results here, but try this:

java AbrtReceiver 10005 650 0.4 5678

It should produce two premature timeouts in a row (on data 1 and the retransmission of data 1) by delaying the ACKs by 1000ms and 1266ms. Convince yourself that the operation of your program is correct.

Submission

You must name your source files AbrtSender.java and AbrtReceiver.java (note the capitalization). 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