Mimicking some features of TCP.

• Implemented cumulative acknowledgment
• Implemented sliding window
• On the sender side, ran a thread for sending packets and a thread for receiving ACKs, used semaphores to solve race condition
• When the receiving thread detected 3 duplicate ACKs and the sending thread was sleeping, it woke up the sending thread, enabling fast re-transmission
• On the receiving side, used a HashMap to receive packets that might be out of order, and only wrote them into memory once a sorted set of packets forming a complete message was received
• Set only one timer and re-transmitted only one packet that did not receive ACK at a time

• When I wrote this program, I hadn’t read Code Complete 2, so I didn’t know that declaring too many global variables would hurt readability, don’t learn this from me!
• At the time I didn't know that Java has a built-in log API, so I use print and file.write