Postacademic Interuniversity Course in Information Technology – Module C1p1 Chapter 1 Evolution of Communication Networks

Postacademic Interuniversity Course in Information Technology – Module C1p2 Contents The 19th century telecommunications –Telegraph - Telephone –Digital vs. analog communications The voice networks & the data networks The electronics revolution ( ) –Digital sound –Mainframe computers with remote access –The first unification : ISDN –Local area networks –Wide area and local area networks integration The Internet –The research project –The universal computer communications medium –The successful unification ?

Postacademic Interuniversity Course in Information Technology – Module C1p3 Contents The 19th century telecommunications –Telegraph - Telephone –Digital vs. analog communications The voice networks & the data networks The electronics revolution ( ) –Digital sound –Mainframe computers with remote access –The first unification : ISDN –Local area networks –Wide area and local area networks integration The Internet –The research project –The universal computer communications medium –The successful unification ?

Postacademic Interuniversity Course in Information Technology – Module C1p4 The Chappe Telegraph (Claude Chappe, ) 92 out of 256 (= 4*8*8) positions represented characters. Integrity of message could be restored at each relay station In 1844, 534 relays linked Paris with 29 cities, covering in total 5000 Km.

Postacademic Interuniversity Course in Information Technology – Module C1p5 The Morse Telegraph Samuel Morse, First electrical telegraph demonstrated in 1837

Postacademic Interuniversity Course in Information Technology – Module C1p6 The Morse Telegraph Signal strength can be restored by means of electromechanical relays connecting separate telegraphic circuits. On land lines, unlimited distances can be covered, without increasing significantly the error rate.

Postacademic Interuniversity Course in Information Technology – Module C1p7 The Telephone Graham Bell, 1876.

Postacademic Interuniversity Course in Information Technology – Module C1p8 Analog vs. Digital Almost infinite number of states External perturbations can not be distinguished from original signal (superposed noise) Information degrades along the lines Finite, small, number of states Most external perturbations can be distinguished from original signal Information can be restored in relays 6:12 Analog Digital

Postacademic Interuniversity Course in Information Technology – Module C1p9 Digital Techniques Representation of numbers in electronic devices ? Binary numbers (base 2) are used. A binary digit (bit) can be represented by a switch: –Value 0 : switch open –Value 1 : switch closed A number with n bits can take 2 n different values –2 bits : 4 combinations –3 bits : 8 combinations –8 bits (= 1 byte) 256 combinations –16 bits: combinations –24 bits: combinations –32 bits: combinations

Postacademic Interuniversity Course in Information Technology – Module C1p10 Contents The 19th century telecommunications –Telegraph - Telephone –Digital vs. analog communications The voice networks & the data networks The electronics revolution ( ) –Digital sound –Mainframe computers with remote access –The first unification : ISDN –Local area networks –Wide area and local area networks integration The Internet –The research project –The universal computer communications medium –The successful unification ?

Postacademic Interuniversity Course in Information Technology – Module C1p11 The Telephone Full mesh network n*(n-1) 2

Postacademic Interuniversity Course in Information Technology – Module C1p12 The Telephone With central switchboard n

Postacademic Interuniversity Course in Information Technology – Module C1p13 Automatic Exchange (1920) Conversation with switch operator replaced by signaling protocol - Voice: analog - Signaling: digital

Postacademic Interuniversity Course in Information Technology – Module C1p14 The Telephone Network PABX SW PABX SW Trunk lines

Postacademic Interuniversity Course in Information Technology – Module C1p15 Telex Networks ( ) Morse code replaced by Baudot or ASCII code

Postacademic Interuniversity Course in Information Technology – Module C1p16 Alphabetical Codes

Postacademic Interuniversity Course in Information Technology – Module C1p17 ASCII Character Set (7 bit) ! “ # $ % & ‘ ( ) * +, -. / : ; < = > ? A B C D E F G H I J K L M N O P Q R S T U V W X Y Z [ \ ] ^ _ ` a b c d e f g h i j k l m n o p q r s t u v w x y z k { | } del nul soh stx etx eot enq ack bel bs ht lf vt ff cr so si dle dc1 dc2 dc3 dc4 nak syn etb can em sub esc fs gs rs us

Postacademic Interuniversity Course in Information Technology – Module C1p18 Unicode (16 bit) FFFF = ASCII Latin,Greek,Cyrillic, and Armenian Arabic and Hebrew Indic Punctuation, math, graphics Chinese / Japanese / Korean symbols Unified Chinese / Japanese / Korean ideographs Private applications

Postacademic Interuniversity Course in Information Technology – Module C1p19 The Dual Networks Voice Network Analog+Digital Data Network Digital