Communication Networks Lecture 23: Presentation Layer and Data Encoding - Prof. Thomas C. , Papers of Organizational Communication

Download Communication Networks Lecture 23: Presentation Layer and Data Encoding - Prof. Thomas C. and more Papers Organizational Communication in PDF only on Docsity! End-to-End Data ENEE 426 | Communication Networks | Spring 2009 Lecture 23 Presentation Layer • Want to convey data to someone remotely • Applications display data • Need standard way to represent data so different applications can display it • Data Encoding – ASN.1 Encoding – eXtensible Markup Language (XML) • Multimedia Encoding – Image Compression – Audio/Video Codecs Slide # 2 ENEE 426 | Communication Networks | Spring 2009 Lecture 23 Markup Languages • Most Common: HTML – Used by web browsers – Tags define text properties • Intermingled with data • Broader: XML Slide # 5 ENEE 426 | Communication Networks | Spring 2009 Lecture 23 XML Example <recipe name="bread" prep_time="5 mins" cook_time="3 hours"> <title>Basic bread</title> <ingredient amount="3" unit="cups">Flour</ingredient> <ingredient amount="0.25" unit="ounce">Yeast</ingredient> <ingredient amount="1.5" unit="cups" state="warm">Water</ingredient> <ingredient amount="1" unit="teaspoon">Salt</ingredient> <instructions> <step>Mix all ingredients together.</step> <step>Knead thoroughly.</step> <step>Cover with a cloth, and leave for one hour in warm room.</step> <step>Knead again.</step> <step>Place in a bread baking tin.</step> <step>Cover with a cloth, and leave for one hour in warm room.</step> <step>Bake in the oven at 350(degrees)F for 30 minutes.</step> </instructions> </recipe> Slide # 6 ENEE 426 | Communication Networks | Spring 2009 Lecture 23 XML Schema and Namespaces • Schema – Defines valid tags, and data type – Allows syntax checking on XML – Schema is an XML file using XMLSchema Schema • Namespaces – Names not necessarily unique between schemas – Use two schemas together – Need a way to uniquely refer to each Slide # 7 ENEE 426 | Communication Networks | Spring 2009 Lecture 23 Run-Length Encoding Slide # 10 ENEE 426 | Communication Networks | Spring 2009 Lecture 23 Differential Pulse Code Modulation • DPCM • AABBCDDDD • A = reference symbol • Encoded: A0001123333 – Values 0-3 can be represented as 2 bits rather than 8 bits • Works better than RLE for digital images – Slow changes in color values Slide # 11 ENEE 426 | Communication Networks | Spring 2009 Lecture 23 Dictionary-Based Methods • Lempel-Ziv (LZ) compression • Dictionary: – List of indexed words • In source document, replace instances of dictionary words with index into dictionary • Dictionary source? – Data-specific – GIF compression: indexed colors Slide # 12