Transmission Control Protocol (TCP)

                 Transmission Control Protocol

   The Transmission Control protocol is a connection oriented reliable protocol. It provides a reliable transport service between pairs of processes executing on end systems using the network layer service provided by the ip protocols.

            1)    TCP is a connection-oriented protocol

            2)    The speed for TCP is slower than UDP

            3)    TCP gives guarantee that the order of data at receiving end is same as on sending.

            4)    TCP does error checking and error recovery. Erroneous packets are retransmitted from the source to the destination.

            5)    Acknowledgement segments

            6)    TCP is used for application that require high reliability.

7)    Its Perfume Three-way handshake- SYN, SYN-ACK, ACK

8)    HTTP, HTTPs, FTP, SMTP, Telnet

9)    TCP header size is 20-24 bytes.

   It's perform three-way handshake: -

1)    Send Synchronization

2)    Receive Synchronization and acknowledgment 

3)    Send acknowledgment 

There are 12 fields in TCP Header: -

1)     Source Port                   (16 bits)

2)     Destination Port          (16 bits)

3)     Sequence Number       (32 bits)

4)     Acknowledgment        (32 bits)

5)     Data Offset                     (4 bits)

6)     Reserved                        (6 bits)

7)     Flag                                  (6 bits)

8)     Window Size                 (16 bits)

9)     Checksum                      (16 bits)

10)Urgent Pointer              (16 bits)

11)Option                             (24 bits)

12)Padding                           (6 bits)

Source Port & Destination Port: - The TCP port number that are to use to communicate endpoints for sending and receiving devices.

Sequence Number: - Message Sender use sequence number to mark the ordering of a group of message.

Acknowledgment: - The Acknowledgment control bit is set in this field to inform the value of next sequence number the sender of the segment is expecting to receive.

Data Offset: - The data offset field use 32 bits' words in tcp header to indicate where the data begins.

Reserved: - Reserved field for future use, it must be Zero.

Window: - a TCP sender use a number called window size to regulate how much data they send to a receiver before requiring an acknowledgment in return.

Checksum: - The Checksum used because TCP doesn't trust the lower
layers and checks everything. The Checksum check the header and data Felds.

Urgent Pointer: - The urgent pointer inform current sequence number, in octets, where the segment of
urgent data begins.

Option: - In option field MSS, Window Scaling, Sack, Timestamps and NOP are use.

TCP Flags: -

1)     URG: Urgent pointer field Signification

2)     ACK: Acknowledgment Field Signification

3)     PSH:  Push Function

4)     RST:  Reset the Connection

5)     SYN: Synchronize Sequence Numbers

6)     FIN: NO more data from sender

TCP Options: -

1)     Maximum Segment Size (MSS 4 bytes): - the maximum segment size is use to define the maximum segment that will be used during a connection between two hosts.

You should only see this option used during the SYN and SYN/ACK phase of the 3-way-handshake.

2)     Window Scaling: - Window scaling was introduced in RFC 1072 and refined in RFC 1323. window scaling simply extends the 16-bit window field to 32 bits in length.                      

3)     Selective Acknowledgment: - SACK is a process which corrects this behavior in the way of multiple dropped segment with selective Acknowledgment.                                      

4)     TIME-STAMPS: - Its define, How Long TCP will wait before attempting to retransmit a segment that has not been acknowledgment.                                                                          

5)     NOP: - TCP NOP option means TCP not use any option.     


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