Looks like you are confused with the word protocol. SOAP is a message exchange protocol. There are differences in message exchange protocol and communication or transport protocol. The TCP/IP you are refering is a transport protocol. SOAP is an information exchange protocol that you sent a message in some specific format that the receiver on other hand understands it. The HTTP, which is on top layer of the TCP/IP stack is used to transport (or transfer) SOAP messages. Although SOAP can be implemented directly to use transfer using lower layer transfer protocol like UDP and even TCP, HTTP/HTTPS is what has been used widely.

I hope with this concept you can explore further.