The choice of HTTP/1.1 as the application data exchange protocol leads directly to the use of TCP as the transport protocol. IETF RFC 7230 states that:
“HTTP messaging is independent of the underlying transport- or session-layer connection protocol(s). HTTP only presumes a reliable transport with in-order delivery of requests and the corresponding in-order delivery of responses. The mapping of HTTP request and response structures onto the data units of an underlying transport protocol is outside the scope of this specification.”
Hence, albeit that other transport protocols may be used to carry HTTP, they are required to provide reliable transport. Clearly, the de facto choice is TCP (IETF RFC 793).