• Passing simple data types (by value) such as integers, floating point numbers and strings (character arrays) is easy. The client-stub simply places copies of them in a calling packet.

• At worst, data types may need format conversion between machines (performed by the Presentation Layer). There exists a well defined data interchange standard - the External Data Representation (XDR) for transferring data between heterogeneous environments (in [RFC1014]).

• To get an appreciation of the complexity of XDR, read the manual entry for xdr or the header file (on Linux).

• Trouble arises when reference parameters must be passed. When local procedures are invoked a reference parameter, such as a pointer may be passed and followed by the procedure (they have the same address space).

This is not true of RPCs!