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)