/TCP-over-UDP

An implementation of a custom TCP-like reliable data transport protocol over UDP

Primary LanguageJava

TCP-over-UDP

Introduction

  • This is an implementation of a custom TCP-like reliable data transport protocol over UDP
  • We name this protocol RDT (for Reliable Data Transport Protocol)
  • Following functionalities have been added over UDP to make it reliable:
    1. Single and cumulative ACKnowledgement
    2. Sequence numbering
    3. Re-transmission
    4. Detecting duplicates and discarding them
    5. Congestion/flow control
  • Just for demonstration purposes, the server has been set to reply back with an uppercased version of the string it receives from client

Repository structure

  • src/ contains the source code
    • src/RDTPacket.java describes structure of a RDT packet
    • src/RDTSocket.java and src/RDTServerSocket.java contain client socket and server socket implementations of RDT, respectively
    • src/Client.java and src/Server.java contain client and server applications, respectively (both use RDT to communicate)
  • compile.sh bash shell-script can be used to compile required source files

Build

  • First compile by cd-ing into the root of this repository and then running command ./compile.sh
  • To start the server,
    • Execute java -classpath bin Server <port_no> where port_no is the port number at which you want to start the server
    • For example, execute java -classpath bin Server 1024 if server is to be started at port number 1024
  • To start client,
    • Execute java -classpath bin Client <ip_addr> <port_no> where ip_addr, port_no are IP address of server and port number, respectively
    • For example, execute java -classpath bin Client 192.168.1.15 1024 is server's IP is 192.168.1.15 and port number is 1024

Example run

  1. Client first sends string Hello followed by Is this working alright?
  2. Consequently, server replies first with HELLO followed by IS THIS WORKING ALRIGHT?
  3. Client output 
    java -classpath bin Client 192.168.1.15 1024
type "quit" to exit session
Hello
--windowSize = 5
--dropping packet seq=#0
--timeout packet seq=#0, retransmitted this packet
--exiting slow start phase
--cwnd decreased from 5.000000 to 2.500000
--received ack with ackNumber=#5, rwnd=9
--windowSize = 9
--sending packet seq=#5
--received ack with ackNumber=#6, rwnd=9

--received packet seq=#0
--received 'HELLO', delivered to upper layer
--acked with ackNumber=#5, rwnd=9
--received packet seq=#5
--received '
', delivered to upper layer
--acked with ackNumber=#6, rwnd=9
Client received: HELLO

Is this working alright?
--windowSize = 5
--dropping packet seq=#0
--timeout packet seq=#0, retransmitted this packet
--exiting slow start phase
--cwnd decreased from 5.000000 to 2.500000
--received ack with ackNumber=#5, rwnd=9
--windowSize = 9
--sending packet seq=#5
--received ack with ackNumber=#10, rwnd=9
--windowSize = 9
--sending packet seq=#10
--received ack with ackNumber=#15, rwnd=9
--windowSize = 9
--dropping packet seq=#15
--timeout packet seq=#15, retransmitted this packet
--cwnd decreased from 12.500000 to 6.250000
--received ack with ackNumber=#20, rwnd=9
--windowSize = 6
--dropping packet seq=#20
--timeout packet seq=#20, retransmitted this packet
--cwnd decreased from 6.250000 to 3.125000
--received ack with ackNumber=#25, rwnd=9

--received packet seq=#0
--received 'IS TH', delivered to upper layer
--acked with ackNumber=#5, rwnd=9
--received packet seq=#5
--received 'IS WO', delivered to upper layer
--acked with ackNumber=#10, rwnd=9
--received packet seq=#10
--received 'RKING', delivered to upper layer
--acked with ackNumber=#15, rwnd=9
--received packet seq=#15
--received ' ALRI', delivered to upper layer
--acked with ackNumber=#20, rwnd=9
--received packet seq=#20
--received 'GHT?
', delivered to upper layer
--acked with ackNumber=#25, rwnd=9
Client received: IS THIS WORKING ALRIGHT?
  4. Server output 
    java -classpath bin Server 1024
accepted connection from 192.168.1.15 at 50233
--received packet seq=#0
--received 'Hello', delivered to upper layer
--acked with ackNumber=#5, rwnd=9
--received packet seq=#5
--received '
', delivered to upper layer
--acked with ackNumber=#6, rwnd=9
Server received: Hello

--windowSize = 5
--dropping packet seq=#0
--timeout packet seq=#0, retransmitted this packet
--exiting slow start phase
--cwnd decreased from 5.000000 to 2.500000
--received ack with ackNumber=#5, rwnd=9
--windowSize = 5
--sending packet seq=#5
--received ack with ackNumber=#6, rwnd=9

--received packet seq=#0
--received 'Is th', delivered to upper layer
--acked with ackNumber=#5, rwnd=9
--received packet seq=#5
--received 'is wo', delivered to upper layer
--acked with ackNumber=#10, rwnd=9
--received packet seq=#10
--received 'rking', delivered to upper layer
--acked with ackNumber=#15, rwnd=9
--received packet seq=#15
--received ' alri', delivered to upper layer
--acked with ackNumber=#20, rwnd=9
--received packet seq=#20
--received 'ght?
', delivered to upper layer
--acked with ackNumber=#25, rwnd=9
Server received: Is this working alright?

--windowSize = 5
--sending packet seq=#0
--received ack with ackNumber=#5, rwnd=9
--windowSize = 9
--sending packet seq=#5
--received ack with ackNumber=#10, rwnd=9
--windowSize = 9
--dropping packet seq=#10
--timeout packet seq=#10, retransmitted this packet
--exiting slow start phase
--cwnd decreased from 15.000000 to 7.500000
--received ack with ackNumber=#15, rwnd=9
--windowSize = 7
--sending packet seq=#15
--received ack with ackNumber=#20, rwnd=9
--windowSize = 7
--dropping packet seq=#20
--timeout packet seq=#20, retransmitted this packet
--cwnd decreased from 7.500000 to 3.750000
--received ack with ackNumber=#25, rwnd=9