synchronization flag (TCP) (SYN)
In the TCP header, the synchronization flag(SYN) is a 1-bit indicator in the control flag field. With a set flag, the sender informs the receiver that it wants to establish a connection.
The Transmission Control Protocol (TCP) can open multiple connections simultaneously. After a connection is opened, the sender sends a synchronization packet to the receiver.
The connection establishment is initiated by host 1, which sets the SYN flag in the TCP header. This indicates to Host 2 that it wants to establish a connection under a specific sequence number. Host 2 confirms the connection setup with an acknowledgement flag( ACK). Then the individual segments, which in the TCP protocol are information units of the transport layer, are sent and confirmed one after the other.