We have implemented the extra part of etternet. The source file of extra part can be found in etthernet.py

This is relatively a much more complex assignment than the previous ones. We finished the project in the following steps:

1. Read the requirements and finished the initial design. We decided to put each layer in different files, which will be good to test and extend.
2. Do the http part. In this part, we basically did similar things to project2. We put a normal socket in tcp.py and build everthing in the application layer in http.py. 
3. Then we started to do things in transport layer and ip layer. We found that ip header are easier so we did the ip header first. 
4. After build the ip header. We started on tcp layer. 
	a) SYN
	b) Receive SYN ACK from server
	c) Send ACK
	d) Send HTTP request
	e) Receive ACK
	f) Receive data and send back ACK.

  We did this one by one and step by step. In the meantime, we put the reusable funtions into utilities.py. 
5. After finishing the basic functionalities, we added the checksum validation, basic congestion control, out-of-order packet handling, duplicatate packet handling and so on.
6. Finally, we build the etthernet part.

The most challenge part was debugging, cause it is really hard to set breakpoint in network code, luckily we found tcpdump was useful on that.

I wrote a small test.sh file to download 2MB, 10MB and 50MB files with both my code and wget, then compare both with md5sum.