DESCIPTION OF OUR APPROACH
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We divided project into sub-tasks, handled them individually and then integrated the results together:
 - Creating appropriate raw sockets and make sure they are sending and receiving data without protocol error
 - Contructing the IP and TCP headers using struct pack
 - Calculate the checksum of TCP header
 - implement 3 way handshake 
 - implement congestion control mechanism
 - handle out of order packets
 - tear down the connection after receiving the complete data
 - verify the checksum of receiving packet
 - construct the HTTP GET request and verify the header
 - parse the given URL and extract the Host name and path name
 - extract body from HTTP response
 - developed ARP request and response module in parallel
 
 
 ARP and ethernet implementation: 
 - construction of ARP frames such that the destination IP is the IP of the gateway
 - the gateway IP was calculated using the subnet mask and the IP of the system
 - the ARP reply was then inspected and the MAC address of the gateway was later found from it
 - after finding out the MAC address , each and every outbound ethernet frame will have the above determined MAC address


 TCP/IP FEATURES IMPLEMENTED:
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1. Basic HTTP: Constructed a simple HTTP GET request and later verify the response for 200 OK code and extract the body

2. TCP : The following,
 
 - constructing TCP segments and calculating checksums
 - Intial Handshake mechanism
 - Congestion control mechanism with initial cwnd = 1 with a timeout functionality
 - Handling out of order packets 
 - Verification of checksum of received packets
 - Graceful teardown

3. IP : 
 - construction of IP datagrams
 - receiving IP datagrams and extracting the length, protocol and other fields for checksum verification 
 
4. ARP and Ethernet:
 - construction of ARP frames
 - determining the MAC address of the gateway
 - construction of ethernet packets
 


 CHALLENGES FACED 
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1. Finding the exact the combo of domain,family and protocol for receiving socket was quite tricky.
2. Managing the sequence and ack numbers during the communication
3. Implementing congestion control mechanism was little tricky as well.
4. Removing the extra characters from the HTTP chunked responses was initially challenging, but got resolved later easily 
 by using HTTP/1.0
5. Since the ARP request is a broadcast message and since the receiver socket is in promiscuous mode , there were too many packets being recieved
 we had to make sure that we picked the right packets that belonged to the response from the gateway , which was later used while constructing 
 ethernet packets.
 
 TESTING 
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1. Tested with several URLs within college intranet that include 2MB,10MB and 50MB log files too. Verified using diff and md5sum