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Introduction 1
EECS 3213 Communication Networks
Introduction, Message & Circuit Switching
Andriy Pavlovych
First Lecture
Introduction 2
Introduction 3
Smoke signals (another example)
Fumata nera
Fumata bianca
Introduction 4
CSE3213 “Communication Networks”
Course Web-Pagewww.eecs.yorku.ca/course/3213/
go there for notes and updates
Instructor Andriy Pavlovych (andriyp@cse)
Pronunciation: Ahn-DREE PavlOHvych
Textbooks Data Communications and Networking", B. A. Forouzan,
McGraw Hill, 2013, 5th edition
“Communication Networks: Fundamental Concepts and Key Architectures”, A. Leon-Garcia and I. Widjaja, McGraw Hill, 2004, 2nd edition
Other recommended reading: see course web-page
Introduction 5
Evaluation (tentative)
Quizzes (2, wks 5 – May 31, 10) 16 %Labs/Assignments (2, released on wks 8, 10) 14 %Midterm (June 14 or 21) 25 %Final (Aug 2–11) 45 %
All dates are approximate and are subject to change
Introduction 6
Missed evaluationsMissed Quizes
Makeups of missed Quizzes will NOT be possible Exact time of each Quiz will be announced on the
course Web site in advanceMissed Midterm
Makeups of missed midterm exams are only possible in exceptional situations, by arrangement well prior to the exam
Introduction 7
Rules during lectures
Eating is allowed
No rotisserie chicken or tortilla chips please!
No C2H5OH (or any R–OH)-containing stuff
No sound emitting devices
If you desperately need to speak to a friend, do so quietly
If you arrive late, find a seat and sit down quietly
If you really need to leave, do it quietly
Introduction 8
Course OutlineDistinction between information and data, between signal
and data, between symbol and data, and between analogue and digital data
Transmission media; time domain and frequency domain Fundamental limits due to Shannon and Nyquist Protocol hierarchies; the OSI model Encoding of analogue/digital data as analogue/digital
signals Data link protocols; error and flow control Medium access; Ethernet & token passing systems in LANs Routing of packets in networks, congestion control Internetworking
Introduction 9
Communication Networksand Services
Overview
Introduction 10
History of Communication
Introduction 11
Same, in a more condensed form
Introduction 12
Communication
In this course: interested in telecommunication
Communication over distance
Image credit: N. Vlajic
Introduction 13
Transmission Medium
Paper
Audio (sound) signals Bells, drums, vuvuzelas…
Optical (visible) signals
Telegraph, smoke…
Introduction 14
Electromagnetic signals
Introduction 15
Communication Networks and Services
Communication Network:
set of equipment and facilities that provide a service of transferring information between geographically separated points
Equipment: PCs, hubs, routers, modems
Facilities: cables, wires, air (!) or vacuum (!!)
“Points”: human users, autonomous sensors
Examples: phone, television broadcast, computer networks (incl. the Internet)
Introduction 16
Evolution of Speed
Telegraph: 20 bps
Telephone/ISDN: 64000 bps
Internet: *high* to *very high*
Introduction 17
Telegraph: Message SwitchingClaude Chappe invented optical telegraph in the 1790’s
Semaphore mimicked a person with outstretched arms with flags in each hand
Different angle combinations of arms & hands generated hundreds of possible signals
Code for enciphering messages kept secret
BTW: “Security by obscurity”
Signal could propagate 800 km in 3 minutes!
Introduction 18
Electrical Telegraphs _Electrical telegraphs
first built possibly by a German inventor Samuel Thomas von Sömmering in 1809
Many wires (one per letter), acid as a detector
Morse telegraph (Samuel Morse, 1837)
Encode text into a digital signal (dots, dashes)
Short/long pulses of current via two wires
2 levels, some addressing and routing inside
Speed of light propagation, yet slow to transmit
No more optical telegraphs!
Introduction 19
Telegraph Networksnetwork of interconnected telegraph stations
(1) a message arrives at a station
(2) operator stores the message until the desired communication line becomes available
(3) operator then forwards the message to next appropriate station
“store and forward” message transmission
Introduction 20
Telephone Networks: Circuit Switching
Telephone: invented by Bell, 1876(Alexander Graham Bell, not Bell Canada)
microphone converts voice pressure variation (sound) into analogue electrical signal
speaker converts electrical signal back into sound
Service for end users, simple to operate
Signal for ae sound, as in ‘cat’
Microphone Loudspeaker
analogelectrical
signalsound sound
Introduction 21
Bell’s Sketch of Telephone
Introduction 22
The N2 Problem
For N users to be fully connected directly
Requires N(N – 1)/2 connections
Requires too much space for cables
Inefficient & costly since connections not always “on”
N = 1000N(N – 1)/2 = 499500
1
2
34
N
. . .
Introduction 23
Telephone Pole Congestion
Introduction 24
Telephone Networks (2)Direct Dedicated Connections
Not practicalCircuit Switched Networks
Fewer wires Human operators at first Auto switches since 1890s
Connection-Oriented Service Connection is set up before
actual information transfer User signals: call setup and tear-down Route: selected during connection setup End-to-end connection across network, continuous (!) Special signaling coordinates connection setup
Introduction 25
Telephone Connection Process
Introduction 26
Computer Network: TCP/IP Protocol Suite
IP protocol is in the middle, IP packet switching
Network-independent platform on which applications can be developed(above)
Independence from the underlying network technologies(below)
Recommended