The External Data Representation

The External Data Representation (XDR) is a standard for the description and encoding of data [RFC1014].

XDR was designed specifically to provide the marshalling and unmarshalling operations for Sun's implementation of RPC.

All data which is transferred in RPC is translated using XDR.

XDR is also useful in situations which do not use RPC, or even the network, as it allows one to read and write arbitrary C data structures in a consistent and well-defined manner.

e.g. We can use XDR to save a program's state (i.e. data structures) to a file so that when the program is restarted it can resume execution where it left off.

XDR fits into the ISO presentation layer, and is roughly analogous to ISO's Abstract Syntax Notation.1.

The major difference between the two is that ASN.1 explicitly sends typing information along with the data while in XDR this information is implied.