JAX-RPC is one of the API’s in the Java Web Serviced Developer Pack.

From the Sun web site:

The JavaTM API for XML-based RPC (JAX-RPC) enables Java technology developers to develop SOAP based interoperable and portable web services. JAX-RPC provides the core API for developing and deploying web services on the Java platform. JAX-RPC is required part of the J2EE 1.4 platform. JAX-RPC web services can also be developed and deployed on J2EE 1.3 containers and Servlet container.

Developers use the standard JAX-RPC programming model to develop SOAP based web service clients and endpoints. JAX-RPC enables JAX-RPC clients to invoke web services developed across heterogeneous platforms. In a similar manner, JAX-RPC web service endpoints can be invoked by heterogeneous clients. JAX-RPC requires SOAP and WSDL standards for this cross-platform interoperability. JAX-RPC is about web services interoperability across heterogeneous platforms and languages. This makes JAX-RPC a key technology for web services based integration.

The JAX-RPC API may be found here.

JAX-RPC was created based on JSR-101.