Information Technology Reference
In-Depth Information
Sequence Numbers
Each segment is sent with a sequence number. At the receiving end, the sequence numbers
re-order segments that might have been received out of order.
Checksum
Each segment is sent with a checksum number. The checksum is verified at the receiving end.
Segments with bad checksum are discarded.
Windowing
TCP uses a window of sequence numbers to implement flow control. The receiver indicates the
amount of data to be sent. The receiver sends a window with every ACK that indicates a range
of acceptable sequence numbers beyond the last received segment . The window allows the
receiver to tell the sender how many bytes to transmit.
Multiplexing
Many processes on a single host can use the TCP protocol. TCP has the capability to multiplex
multiple upper-layer applications into a single connection.
To better understand the mechanics of TCP, look at the TCP header.
TCP Header Format
Understanding the format of the TCP header helps comprehend all the functions and mechanics
of the protocol. TCP uses port numbers, sequence numbers, a sliding window size, and flags in
the header. Figure 6-5 shows the TCP header.
TCP Header
Figure 6-5
0 1 2 3
01234567890123456789012345678901
Source Port
Destination Port
Sequence Number
Data
Offset
Control Bits
(Flags)
Reserved
Window Size
Checksum
Urgent Pointer
Options
Padding
Upper Layer Data
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