External Data Representation
External Data Representation (abbreviated XDR ) is an abstract of technical communication standard was defined by Sun Microsystems and other companies to standardize the exchange of data between servers and clients hardware independent. XDR is an implementation of the presentation layer of the OSI model for network communication, and is firmly established as described in RFC 1014. It was founded in 1995 updated by RFC 1832, which is 128 -bit floating point numbers added, and in 2006 incorporated by RFC 4506, which only structural, but no substantive changes.
Its main application is the standard in communication in the SUN Network File System. A number of programming languages support the reading and writing of XDR data by library functions ( see, for example xdr_ * functions in libc on Unix for C, XDR module for Perl, xdrlib module for Python).
XDR defines a representation for the most common data types such as integers, strings or arrays, however, is untyped itself. The XDR byte order is specified in the current standards on big endian, which is the network byte order of TCP / IP. One XDR unit correspond to 4 bytes. Floating point numbers are encoded in single and double precision according to the IEEE 754 standard.