Update 'Test_Cases/Test_Case2/readme'

Test_Cases/Test_Case2/readme

@@ -1,12 +1,57 @@
 This folder contains detail for Test_Case2.
 
-Source IP        = 192.168.10.20, which is c0a8 0a14 in hex
-Destination IP   = 192.168.10.10, which is c0a8 0a0a in hex
-Source Port      = 2341, which is 0925 in hex,
-Destination Port = 1200, which is 04B0 in hex.
-
+1. Verison = 4, to indicate IPv4 version is used.
+2. IHL = 5, which indicates 20 bytes.
+3. Type of Service = 0,
+4. Total Length = 40, which is 28 in hex. The total windows size contains the total lenght of IP header plus data.
+5. Identification = 0002,
+6. Flags = All flags are set to zero,
+7. Fragment Offset = For now, there is no fragment offset so, this value is set to 0.
+8. TTL = 40s, which is 28 in hex.
+9. Protocol = 6, which indicates TCP.
+10. Header Checksum = initially zero and then changed to the 1's complement of the sum of 16 bit values of IP header + data.
+11. Source IP        = 192.168.10.20, which is c0a8 0a14 in hex
+12. Destination IP   = 192.168.10.10, which is c0a8 0a0a in hex
+13. Source Port      = 2341, which is 0925 in hex,
+14. Destination Port = 1200, which is 04B0 in hex.
+15. Sequence Number = 0 for now,
+16. Acknowledgement Number = 0,
+17. Flags: 
 For the SYN packet, the SYN Flag in the header has a value of 1.
 For the SYN+ACK packet, the SYN and ACK flags in the header have a value of 1.
 For the ACK packet, the ACK flag in the header has a value of 1.
 For the FIN packet, the FIN flag in the header has a value of 1.
-For the FIN+ACK packet, the FIN and ACK flags in the header have a value of 1.
+For the FIN+ACK packet, the FIN and ACK flags in the header have a value of 1.
+18. TCP Checksum = initially zero, then:
+(i) Concatenate TCP Pseudo header (Protocol, Source IP, Destination IP, Total Length) with TCP header and TCP data. This creates a big integer.
+(ii) Convert this integer to binary and compute bit wise 1's complement. 
+19. Urgent Pointer = 0, no urgent data in the header.
+
+The value of header comes out to be:
+header = {}
+header[0] = 0x45, Version, IHL
+header[1] = 0x00, TOS, 
+header[2] = 0x00, Total Length,
+header[3] = 0x28, Total Length, 
+header[4] = 0x00, Identification,
+header[5] = 0x02, Identification,
+header[6] = 0x00, Flags + Fragment Offset,
+header[7] = 0x00, Flags + Fragment Offset,
+header[8] = 0x28, TTL
+header[9] = 0x06, Protocol
+header[10] = 0x00, Header Checksum
+header[11] = 0x00, Header Checksum
+header[12] = 0xc0, Source IP,
+header[13] = 0xa8, Source IP,
+header[14] = 0x0a, Source IP,
+header[15] = 0x14, Source IP,
+header[16] = 0xc0, Destination IP,
+header[17] = 0xa8, Destination IP,
+header[18] = 0x0a, Destination IP,
+header[19] = 0x0a, Destination IP,
+
+The value of IP_Header_Checksum comes out to be: ed1c.
+
+References:
+1. https://www.thegeekstuff.com/2012/05/ip-header-checksum/
+2. https://www.tutorialspoint.com/calculation-of-tcp-checksum