Computer Networks CS 3623 20 Data Transformation What

Computer Networks (CS 3623) #20 | Data Transformation

What is this? • 1011010100001011110100100100 1000100110101001010010101001111010110001101011 101010011001111110101001001 0000101010100101010010101001111010110 0011010100110011111101010010010000101010100100 ……….

Issues • The two sides agreeing to a message format, often called the presentation format • The efficiency of the encoding (data compression)

PRESENTATION FORMAT

Encoding & Decoding Data • Exp: Big / Little Endian

Argument marshalling • converting, packing, and linearizing

Taxonomy • Data types – base, flat, complex • Conversion strategies – canonical intermediate form, receiver-makes-right • Tags – Tagged, untagged • Stub – interpreted. , compiled

Tagged: example • A 32 -bit integer

Stub

Popular network data representations • XDR (External Data Representation) Sun. RPC • ASN. 1 (Abstract Syntax Notation One) ISO • NDR (Network Data Representation) DCE • XML (Extensible Markup Language)

XDR: example

ASN. 1 • (tag, length, value)

XML: example

XML Schema Definition (XSD)

DATA COMPRESSION

Classes • Lossless – Run length encoding (RLE) – differential pulse code modulation (DPCM) – Dictionary-Based Methods: Lempel-Ziv & its variants • Lossy – JPEG – MP 3