The Hypertext Transfer Protocol (HTTP) was designed with TCP as the underlying transport protocol. The Constrained Application Protocol (CoAP), while inspired by HTTP, has been defined to make use of UDP instead of TCP. Therefore, reliable delivery and a simple congestion control and flow control mechanism are provided by the message layer of the CoAP protocol. A number of environments benefit from the use of CoAP directly over a reliable byte stream such as TCP, which already provides these services. This document defines the use of CoAP over TCP as well as CoAP over TLS.