Viewing a sample of TCP transaction messages might be helpful for understanding the protocol.
Download wireshark traces from this link and open tcp-ethereal-trace-1 file with Wireshark. You can find more instructions on this page.
- When submitting your file, please add a readme file with any modifications you made.
- You can receive bonus points if you implement any additional TCP feature or additional error case handling (like What to do if the client never received syn+ack). If you're not sure you're on the right track, please email me. Please, state the additional feature you're implementing, possibly with a citation from the TCP reference.
- You don't need to use
receive_acksfor milestone 1. You can receive and parse a message with
recv_data, addr = sock.recvfrom(1024)
header = utils.bits_to_header(recv_data)User Datagram Protocol (UDP) is a minimal protocol running over IP. In this assignment you will implement a reliable message protocol over UDP. You will emulate a subset of TCP protocol. Features to be implemented are:
- Establish a connections
- Ordered data transfer
- Retransmission of lost packets
We provide you templates for client and server applications for Python 3.
We plan to update this document as it's needed. If there's any major update we'll make an announcement.
Connection setup & teardown, due 3/29
Check the 1 Establish a connection and 3 Tear down the connection sections below.
Data transfer with retransmission of lost packets
Bonus points for any extra features of TCP like flow control.
In essence, you will implement TCP-like protocol within UDP data. UDP data will consist of your protocol's header and body.
Please, read and understand the provided template code. There are three python files are provided.
This file implements States Enum type, header type for your own protocol and some helper functions. You will need to extend these classes for your needs as they are missing some states or fields.
If you set DEBUG = True, it will print extra information as your application is running. If you need to print debug information as you develop application, check this variable before printing. Set this value to False when you're submitting the code.
class States: implements Enum types to represent TCP protocol states.
Read the comments in the file
MSS = 12: we use pretty small segment size to make it easier to test and demo. We will need to divide long messages into a number of packets.
Read the comments in the file
This class represents the Header of your own protocol and provides some helper methods.
The header has 12 bytes. First 4 bytes represent sequence_number, the second 4 bytes represent acknowledge_number and the next two bits represent the syn and ack header fields. The remaining 30 bits are currenctly unused. You can utilize the rest for your needs.
Implement the TCP 3-way Handshake Protocol
Please refer to Connection establishment section: https://en.wikipedia.org/wiki/Transmission_Control_Protocol#Connection_establishment
- Server is waiting for a connection
- Client sends a SYN
- Server replies with SYN-ACK
- Client replies with ACK
UDP is an unreliable protocol. Some of the packages might be lost or received in different order. Implement the TCP-like protocol to retransmit the missing packages. Client should order the packets correctly.
You are free to choose a protocol for retranmission:
- stop and wait
Bonus: TIME_WAIT state implementation is bonus points. You won't lose points if you don't implement TIME_WAIT.
https://en.wikipedia.org/wiki/Transmission_Control_Protocol#Protocol_operation https://tools.ietf.org/html/draft-gg-udt-03