The ITRON TCP/IP API Specification is to define a standard API (Application Program Interface) for a TCP/IP protocol stack suitable for embedded systems. It defines a C-language API for TCP and UDP protocols on IPv4.
The whole specification document can be downloaded from here.
The ITRON TCP/IP API Specification was designed by the Embedded TCP/IP Technical Committee, which was formed with the call from the ITRON Technical Committee, and was approved as an ITRON specification by the ITRON Technical Committee. The announcement on the release of the specification is here.