Answer: Please see below as the answer is self-explanatory
Explanation:
For the TCP/IP protocol suite, the IP protocol is the Network (or Internet) layer (Layer 3 in the OSI model), and TCP is one of the possible options for the Transport Layer, (Layer 4 in the OSI model).
Now, how the transport layer is aware that the transport protocol to be used is TCP?
When the network layer receives a packet, reads the IP Header, processes it, and then, after stripping it from the packet, sends it to the immediate upper layer.
In the IP header, there is a field, that tells the network layer, which is the protocol that will take care of the packet payload once processed by the network layer.
This field, has different names in IPv4 and IPv6; It is called PROTOCOL in IPv4, and NEXT HEADER in IPv6.
It has a length of 8 bits, and the binary value included in it, identifies uniquely the type of upper-layer protocol to be used, being the same for the same protocol in both versions of IP protocol.
For TCP, it is 6 in binary: 00000110.
