CS 5623 Simulation Techniques

Fall 2003
Instructor Dr. Turgay Korkmaz

Homework 5 - programming
Due by Nov 18, 2003 (5:30pm)

100 points

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You are asked to implement a simulation program using CSIM for the below network.

Sa

Da

System:

• Sa and Sb have infinite amount of data to send to Da and Db, respectively.
• Assume Sa and Sb use TCP to reliably transfer their data
• You just need to focus on the congestion control aspect and implement TCP Reno

(YOU NEED TO READ YOUR FAIVORETE COMPUTER NETWORKING BOOK FOR TCP or related sites like http://www.faqs.org/rfcs/rfc2581.html )

But I think the following tutorial would be enough for this hw,

Here is a nice TCP tutorial by J.F Kurose and K.W. Ross (see page 51-96)

• MSS is 500 bytes

• Assume Da and Db will
• drop all the out-of-order packets,
• immediately send ACKs
• immediately consume the received data (so no need to worry about flow control).
• Assume that each link is bi-directional
• Each has capacity of 100 KBps (100*1024 Bytes/sec) in each direction
• For transmission delay only consider the length of IP packet which is 20+20+MSS bytes for data packets and 20+20 bytes for ack packets.
• Propagation delay is 0.001 sec for all links except for Sa-Ra and Sb-Ra
• propagation delay for Sa-Ra is Xa
• propagation delay for Sb-Ra is Xb
• Xa and Xb will be given as simulation parameters
• Assume that all nodes are identical:
• Processing time for any packet (e.g., creating a TCP packet, IP address lookup) is 0.0 sec
• After creating/receiving an IP packet, the CPU puts that packet in the buffer of an appropriate output line
• Each line has a physical device to send packets from its buffer using FIFO scheduling
• Capacity of each output buffer is Buff = B KB (B*1024 Bytes)
• B will be given as a simulation parameter
• Assume that no packet will be corrupted (so no need to worry about computing checksum etc) but some packets might be lost due to buffer overflow at any node or a packet might be lost with probability Loss Prop while propagating between Ra and Rb.
• LossProb will be given as a simulation parameter

Objectives:

See the evolution of

· window sizes Wa and W

· Throughput_a and Throughput_b, and

· Goodput_a and Goodput_b

Over time when different values are given to Xa, Xb, B and LossProb .

Throughput is the observed rate at which data is sent.

In your simulation, you can find it as follows:

In TCP_sender

start_time = clock;

while(1)

….

Thrughput_a(t)= total number of bytes including retransmissions that are sent by sender a until t / (t-start_time)

….

end while

Goodput is the observed rate at which useful data is sent (i.e., retransmitted data should be excluded)

In your simulation, you can find it as follows:

In TCP_receiver

Time_of_first_adrrival = -1.0;

While(1)

….

If Time_of_first_adrrival<0 then Time_of_first_adrrival=clock

Else Goodput_a(t) = total number of bytes excluding retransmissions that are received by receiver a / (t - Time_of_first_adrrival).

….

End while

Initial Conditions and Simulation times:

· All queues are empty

· TCP connections are already established at time 0.0 but before sending the first byte, a tcp sender will hold uniform(1.0, 5.0) sec

· initially Wa=Wb=1 and thresholds Tha=Thb = 5.

· Simulation time is SimTime (in sec) and will be given as a simulation parameter.

For report (please type it)

Run your simulation program with the following parameters and for each run draw the graphs shown below.

Part (a)

Ø hw5 -Xa 0.003 -Xb 0.003 –B 50 -LossProb 0.000 -SimTime 180.0 -s 152

Ø hw5 -Xa 0.003 -Xb 0.003 –B 50 -LossProb 0.001 -SimTime 180.0 -s 152

Ø hw5 -Xa 0.003 -Xb 0.003 –B 50 -LossProb 0.005 -SimTime 180.0 -s 152

Part (b)

Ø hw5 -Xa 0.003 -Xb 0.003 –B 100 -LossProb 0.000 -SimTime 180.0 -s 152

Ø hw5 -Xa 0.003 -Xb 0.003 –B 100 -LossProb 0.001 -SimTime 180.0 -s 152

Ø hw5 -Xa 0.003 -Xb 0.003 –B 100 -LossProb 0.005 -SimTime 180.0 -s 152

Part (c)

Ø hw5 -Xa 0.003 -Xb 0.004 –B 50 -LossProb 0.000 -SimTime 180.0 -s 152

Ø hw5 -Xa 0.003 -Xb 0.004 –B 50 -LossProb 0.001 -SimTime 180.0 -s 152

Ø hw5 -Xa 0.003 -Xb 0.004 –B 50 -LossProb 0.005 -SimTime 180.0 -s 152

A. For each run, draw the following graphs

…..

…………………..

B. In addition to the above figures (9 of them), your report should include the followings:

1. Briefly explain how you modeled this system and implemented your program. Include the hard copy of your program with comments (please after submission, don’t change your soft copy, if needed we will run your original program together)

2. Analyze the results and comment on

· how and why increasing LossProb affect the performance measure in each part

· how and why Xa and Xb affect the performance measures (particularly compare the first run in part (a) and part (c).

· how and why B affects the performance measures (particularly compare the first run in part (a) and part (b).