As we have discussed before, if no TCP existed we would encounter an issue because IP is connectionless. So if a missing packet occurred this would mean we do not have the full sequence of packets. And without a complete sequence of packet for that flow we cannot send this data to the Application Layer.
As we discussed we number every packet and we tell the receiver what sequence number we are starting from for this flow of Data. This is what TCP does.
When the client initiates the first connection, if they do not get a response they have a timer of sorts where they then resend that same packet. It will start with the same sequence number.
TCP is a virtual connection connecting source client TCP to destination client TCP in essence.
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