domidzitac / nanotcp

A open-source TCP/IP implementation in C. Simulated using mininet

TCP-Jia-Komiljon

TCP/IP implementation in C. Simulated using Mininet.

Sample throughput of TCP with near 0 loss.

Base features

• The sender sends packets based on a window.
• The receiver sending cumulative acks to server.
• When a sent packet is acked, the window slides and a new packet is transmitted from the sender.
• All reading and writing operations are done directly to file using fseek

Buffering out of order packets

• If the receiver receives an out of packet, the packet is buffered by writing to the location in disk.
• A circular array is used to track the packets that have been acked.
• On arrival of a new packet, if it completes a buffered sequence, then send cumulative ack.
• If sender did not recieve ack within timeout window, it will re-send the packets.

Congestion mechanisms

1. Slow start:

• The initial ssthresh is set to 64 segments.
• During slow start, the window_size doubles each time a full window has been acked
• Slow start continues until the window_size reaches ssthresh at which point we move to congestion avoidance

2. Congestion avoidance:

• In this phase, window_size will increase by 1 each time a full window has been acked

3. Fast retransmit:

• If the sender receives 3 duplicate_ack then ssthresh is set to half the window_size and window size is set to 1.

Plot of throughput and congestion window with a loss of 0.1%. The gray background is the current throughput of the network.

Run instructions

To run the above simulation, first build from the source by navigating to /rdt2.0/src and running make.

Then, navigate to the root directory and run sudo ./run.sh. Make sure to place a file named FILE in the root directory. This will transfer to a new file named FILE_RCVD.

If you wish to run a checksum, ensure that the FILE is small enough or has enough time to fully be sent by the network. Then simply run cksum FILE FILE_RCVD in the root directory.

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How to run mininet.

sudo mn --link tc,bw=10,delay=10ms,loss=2
mininet> xterm h1 h2

Terminal node h1

./rdt2.0/obj/rdt_receiver 60001 FILE_RCVD

Terminal node h2

./rdt2.0/obj/rdt_sender 10.0.0.1 60001 small_file.bin

Verifying checksum of the two files

cksum FILE_RCVD small_file.bin

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