Explain Control bits (flags) in TCP header.
1 Answer
  1. TCP is a transport layer protocol used by applications that require guaranteed delivery.
  2. The endpoints are defined by an IP address and a TCP port number. TCP works in full duplex mode and has various fields. It provides handling for both timeouts and re-transmission as it follows sliding window protocol.
  3. The TCP header is of 20 byte and the format for data delivery is defined as

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The control bits are as stated as below:

a) Urgent (URG bit 106): It indicates if we need to use Urgent pointer field or not. If it is set to 1 then only we use Urgent pointer.

b) Acknowledgement (ACK bit 107): It is set when an acknowledgement is being sent to the sender.

c) PUSH flag (PSH bit 108): When the bit is set, it tells the receiving TCP module to pass the data to the application immediately.

d) Reset flag (RST bit 109): When the bit is set, it aborts the connection. It is also used as a negative acknowledgement against a connection request.

e) Synchronize flag (SYN bit 110): It is used during the initial establishment of a connection. It is set when synchronizing process is initiated.

f) Final flag (FIN bit 111): The bit indicates that the host that sent the FIN bit has no more data to send.

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