Why is TCP needed if IP packets can be retransmitted when no response is received?

TCP is needed to provide reliable, ordered, and controlled data transfer over IP, which by itself does not guarantee delivery, order, or integrity of packets.

If IP packets are simply retransmitted when there is no response, then:

• There is no guarantee that packets will arrive in the same order.
• There is no mechanism for data integrity control.
• There is no flow control or network congestion management.
• There are no delivery acknowledgments and retransmission of only lost packets.

TCP implements all these mechanisms: connection establishment, acknowledgments, error control, and flow control, making data transfer reliable and convenient for applications.

Thus, TCP is a transport layer protocol built on top of IP that ensures reliability, without which many network applications cannot operate correctly.