What is TCP (Transmission Control Protocol) ?

The TCP / IP protocol is designed to ensure the packet reaches its destination. If the packet does not arrive at its destination, the TCP / IP protocol will send the packet back. Of course this can be done because every packet that arrives at the destination will provide feed back to the source, so that TCP / IP can know a packet received to the destination because of a report or what is called a flag. This made the TCP / IP protocol popular and made it the standard for sending a packet on both the Internet.

TCP / IP header

The TCP / IP header is 20 bytes large, and contains some information that will be carried from the source to the destination host. Each packet sent will be wrapped in the header of the TCP protocol. The following is a table that provides an explanation of each field in the TCP header [6].

Table 2.2 TCP / IP Header Descriptions

No.

Field Name

Information

1. Source Port Port 

from source

2. Destination Port 

Port of destination

3. Sequence Number

Indicates the sequence number of the first octet data.

4. Acknowledgment Number

Indicates the next sequence number of the octet

5. Offset data

Worth 32 bits. This indicates where the data will start.

6. Reserved

Saved for later. Set to 0.

7. Control Bits

Indicates a flag or report of six.

8. Window

Indicates the size of the segment that can be received by the reception.

9. Checksum

Serves to check the integrity of the TCP segment.

Before transferring data, the TCP / IP protocol will make a request to the destination host and then the destination host will provide feedback that the connection is connected. The process of establishing a TCP connection is called a three way handshake. The purpose of this process is to synchronize the sequence numbers and acknowledgments sent by both parties and change the size of the TCP window. Three Handshake

The process can be explained as follows:

1. Host A that wants to connect to host B will first send a SYN flag to host B.

2. After the SYN flag is obtained, host B will send the SYN + ACK flag as a sign that the SYN flag has arrived at its destination.

3. Then host A will send an ACK flag which indicates that the SYN + ACK flag from host B has arrived and this also indicates that host A and host B are connected.