TI-RPC Issues

A number of issues help to characterize a particular RPC implementation.

• How are parameters and results passed?

• How is binding carried out?

• How are transport protocols dealt with?

• What are the call semantics?

• What data representation is used?

Parameter Passing

TI-RPC allows a single parameter to be passed from client to server. If more than one parameter is required, the components can be combined into a structure that is counted as a single element. Information passed from server to client is passed as the function's return value. Information cannot be passed back from server to client through the parameter list.

Binding

The client must know how to contact the service. The two necessary aspects are finding out which host the server is on, and then connecting to the actual server process. On each host, a service called rpcbind manages RPC services. TI-RPC uses the available host-naming services, such as the hosts file and DNS, to locate a host.

Transport Protocol

The transport protocol specifies how the call message and the reply message are transmitted between client and server. TS-RPC used TCP and UDP as transport protocols, but the current version of TI-RPC is transport independent, so it works with any transport protocol.

Call Semantics

Call semantics define what the client can assume about the execution of the remote procedure; in particular, how many times the procedure was executed. These semantics are important in dealing with error conditions. The three alternatives are exactly once, at most once, and at least once. ONC+ provides at least once semantics. Procedures called remotely are idempotent: they should return the same result each time they are called, even through several iterations.

Data Representation

Data representation describes the format used for parameters and results as they are passed between processes. To function on a variety of system architectures, RPC requires a standard data representation. TI-RPC uses external data representation (XDR). XDR is a machine-independent data description and encoding protocol. Using XDR, RPC can handle arbitrary data structures, regardless of the byte orders or structure layout conventions of the different hosts. For a detailed discussion of XDR, see Appendix A, XDR Technical Note and Appendix C, XDR Protocol Specification.