This is Carl,??? (confirming the server??™s acknowledgement). Once we have established the
connection with one another, we proceed to exchange information with each other.
Once the TCP connection is established, the client and server begin to exchange messages and data.
The TCP protocol uses sequence numbers to indicate the order in which pieces of the total message go together.
Both the client and server exchange initial sequence numbers (ISNs) during the connection establishment
exchange. One number is used for messages from the client to the server, and one is used for messages in the
other direction.
When the client sends a message, the client labels the message with a sequence number. The client expects the
server to acknowledge receipt of the message by responding with a sequence number one greater than the one sent.
If the client does not receive confirmation of a message it sent within a set period of time, the client assumes
that the message was lost, and the client sends the same message, with the same sequence number, again.
On the server side, the server can use the sequence numbers to determine if it receives the same message
twice. If a client mistakenly sends a message twice when the server already received the message, the server
can simply discard the duplicate message.
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