Description

Part A
Transport Layer

In this part, we will learn how to create our own congestion control protocol in ns3( 3.29).
NS-3 by default uses TcpNewReno as the congestion control strategy (Link). It consists of
the following functions of interest to us
1. TcpNewReno::SlowStart:
“ns-allinone-3.29/ns-3.29/src/internet/model/tcp-congestion-ops.cc”
2. TcpNewReno::CongestionAvoidance:
“ns-allinone-3.29/ns-3.29/src/internet/model/tcp-congestion-ops.cc”
Our goal will be to create a new congestion control algorithm called TcpNewRenoPlus. For
this, you need to create 2 new files TcpNewRenoPlus.cc and TcpNewRenoPlus.h in
“ns-allinone-3.29/ns-3.29/src/internet/model”. You can refer to the following link on how to
write a new congestion control algorithm in NS-3.
You need to reuse most of the code of TcpNewReno from
“ns-allinone-3.29/ns-3.29/src/internet/model/tcp-congestion-ops.cc” and
“”ns-allinone-3.29/ns-3.29/src/internet/model/tcp-congestion-ops.h” and the algorithmic
changes need to be done only for the SlowStart and CongestionAvoidance functions in your
TcpNewRenoPlus.cc.
The way you implement it by using inheritance of base class TcpCongestionOps /
TcpNewReno /or any other way is your decision. The important point is that all functionalities
in TcpNewRenoPlus except the below two should be of TcpNewReno.
1. TcpNewReno::SlowStart
2. TcpNewReno::CongestionAvoidance
In Slow Start phase of TcpNewRenoNew, increase the congestion window size𝐶𝑤𝑛𝑑 as:
𝐶𝑤𝑛𝑑 = 𝐶𝑤𝑛𝑑 + (𝑆𝑒𝑔𝑚𝑒𝑛𝑡𝑆𝑖𝑧𝑒)
1.91
/𝐶𝑤𝑛𝑑
In the Congestion Avoidance phase of TcpNewRenoPlus, update the congestion window
as
𝐶𝑤𝑛𝑑 = 𝐶𝑤𝑛𝑑 + 0. 51 * 𝑆𝑒𝑔𝑚𝑒𝑛𝑡𝑆𝑖𝑧𝑒
In order to understand the behavior of the network using the newly designed
congestion control protocol, we will use the topology described in Figure 3 below.
Figure 1
In Figure.1, N2-N3 and N1-N3 are connected via a point-to-point link. DR means
Data Rate of the channel. Here we have TCP source at N1 and N2 and TCP sink at
N3.
We will use the below 2 configurations of the network described in Fig.1 to analyze
the behavior of congestion control algorithms:
● Configuration1: All senders use TCPNewReno.
● Configuration2: All senders use TCPNewRenoPlus.

For both two configurations above, the following hold:

i) Application data rate: 1.5 Mbps
ii) Connection 1 starts at time 1sec, Connection 2 starts at time 5sec,
Connection 3 starts at time 15sec.
iii)Connection 1 ends at time 20sec, Connection 2 ends at time 25sec,
Connection 3 ends at time 30sec.
iv) Packet size is 3000 bytes.
v) At N3 use RateErrorModel as the error model with error rate as 0.00001.

You need to answer the following questions:

For each configuration do the following at each TCP source.
1. Plot Congestion window size vs time (from t=1 to t=30 seconds)
2. How does the congestion avoidance phase vary on the same sender when using
TCPNewRenoPlus vs TCPNewReno? Explain the observed trends. How does it
impact the entire network?

What to Submit for Part A

1. For each part, write your answers, observations, plots and hypotheses in a single
report file.
2. Submission folder should be a single .zip or .tar.gz file containing a report file and
code for each question. Follow the directory structure as given below.
PART A/-
Entry_number_Report_partA.pdf
Congestion/-
TcpNewRenoPlus.cc
TcpNewRenoPlus.h
Congestion_topology_files/-
First.cc etc.
In case you are using any other helper code/libraries to generate plots, submit
that code for generating plots.
3. The plots can be generated either using the .cc files or any other tool you wish to
choose such as Python. But make sure, that plot is generated just using commands
and not by copy pasting data values manually in excel or something like that during
the demo. (Tip : Save the output values in a separate file and write a script to
process that file and generate plots).
4. For each code file/package/libraries you submitted in the assignment, clearly
describe their purpose in the report (1 to 2 sentences are enough for each).

Part B:
Network Layer
Routing Information Protocol

For this part we will refer to the following as base file
“ns-allinone-3.29/ns-3.29/examples/routing/rip-simple-network.cc”
You need to make the following changes in the base networking model.
1. Create a network topology of the form
Fig.2
R1, R2, R3 are RIPng routers( similar to what used in the base file).
2. All interfaces have metric =1( all networks have cost=1).
3. Use split horizon as default.
4. The Source and Dest will exchange packets as done in the base file.
5. On similar lines as in the base file, for this topology(fig.2) R1 and R3(where
R1 is connected to Source and R3 is connected to Dest), are configured with
static addresses. Refer to base file and change if required.
Part B.i)
In this part we will study how the convergence time of routing table varies with
different channel delays. The data rate is fixed for this experiment (5000000 i.e
(csma.SetChannelAttribute (“DataRate”, DataRateValue (5000000));).
Questions
a) Run the simulation with the following different delays in CSMA channel
[100, 1000, 20000, 80000]. All values in millisec
For each delay value, create a plot where x-axis represents time(in seconds) and y
-coordinate shows whether all routing tables have converged or not at that point of time.(
The y-coordinate will have value 1 if all routing tables have converged at that particular
time else 0). For each plot, show the y-coordinate values at Time
stamps x = 0, 10, 50, 100, 500( all values in sec).
For this question, you generate 4 plots(corresponding to each delay)
b) Explain the trend observed in part a). Why does this behavior happen?
For PartB.ii and PartB.iii) the data rate is fixed to
5000000(csma.SetChannelAttribute (“DataRate”, DataRateValue (5000000));) and
Delay is set to 2 Milliseconds.
Part B.ii): In this part we simulate link going down and its impact on routing
tables and reachability.

Simulate the following:

The link between R1 and R2 goes down at t=50 sec. The link between R1 and R3
goes down at t=120 sec.
Questions
a) Print the routing table for all routers at t=121 sec and t=180 sec. For your
tables, label which table is for which routing table(like R1, R2 R3). No marks
will be awarded without this. First display the tables at t=121 sec then
display the tables at t=180 sec.
b) Create a plot where on x-axis we have the time(t in sec) and on y-axis we plot
whether the destination(DEST) node is reachable from the source
node(SOURCE). ( y-coordinate has value 1 if dest at time t is reachable else 0). Do
this for t = 49, 51, 60, 119, 121, 150( all values in sec).
c) In part b above, what is the similarity/difference between the reachability
behavior at t=51sec vs at t=119sec vs at t=121sec? Explain why does it
happen.
Part B.iii) Simulate the following(this question is independent of PartB.ii)
The link between R1 and R2 goes down at t=50sec. The link between R1 and R3
also goes down at t=50sec. The link between (R1 and R2) and between (R1 and R3
) comes up at t= 120sec.

Questions

a) Print the routing table for all routers at t=70sec and t=180sec. For your routing
tables, label which table is for which routing table(like R1, R2, R3). No marks
will be awarded without this. First display the tables at t=70sec then display
the tables at t=180sec.
b) Create a plot where on x-axis we have the time(t in sec) and on y-axis we plot
whether the destination node is reachable from the source node. ( y-coord
has value 1 if dest is reachable from src else 0). Do this for t = 119, 121, 140, 200( All
values in seconds.)

What to submit for Part B

Report(file name EntryNumber_Report_PartB) and your .cc file(s). Any other
scripts such as .sh files required to call your program with arguments etc.
Overall submission details for Assignment 4
Create a folder(i.e home folder with name = Entry Number) having two sub folders (
Part A, Part B).
Submit files(folders) of each part in its folder.
Zip home folder as EntryNumber.zip.