Internet Security - Dang Thanh Binh's Page

Bits
IP
header
TCP/IP SUITE AND INTERNET STACK PROTOCOLS 43
TCP
header
20 bytes 20 bytes
IP datagram
TCP segment
TCP
data
Figure 2.10 Encapsulation of TCP data in an IP datagram.
0 4 10 16 24
31
Header
length
(4 bits)
Source port number (16 bits)
Reserved
(6 bits)
Checksum (16 bits)
Sequence number (32 bits)
Acknowledgement number (32 bits)
Code bits
(6 bits)
TCP option (24 bits)
Data
Figure 2.11 TCP packet format.
Destination port number (16 bits)
Window size (16 bits)
Urgent pointer(16 bits)
Padding (8 bits)
sending and receiving application. These two port numbers, along with the source
and destination IP addresses in the IP header, uniquely identify each connection. The
combination of an IP address and a port number is sometimes called a socket. The
socket pair, consisting of the client IP address and port number and the server IP
address and port number, specifies two end points that uniquely identify each TCP
connection in the Internet.
• Sequence number (32 bits): This 32-bit sequence field defines the sequence number
assigned to the first byte of data stream contained in this segment. To ensure connectivity,
each byte to be transmitted is numbered. This sequence number identifies the
byte in the data stream from the sending TCP to the receiving TCP. Considering the
stream of bytes following in one direction between two applications, TCP will number
each byte with a sequence number. During connection establishment, each party uses
a random number generator to create an initial sequence number (ISN) that is usually
Header