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EE1D01 Electrical Science for Everyone
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Telephone
A telephone is an electronic device used for twoA telephone is an electronic device used for two--way talking with other people.way talking with other people.
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ear
T
R
mouthDTMF
ringer
C
dial switch
SLIC
TelephoneSubscriber
Line
CO(Local Exchange)
cradle switch
off-hookon-hook
tip (+)
ring (-)
Basic Telephone
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hybrid
TTelephone
currentdetector
~
ring switch
ringgenerator
(100Vrms 25 Hz) -48 VDC
SubscriberLine
crossconnectswitch
Subscriber Line Interface Circuit
Processor
control channel
Call Statesidle on hookdialing dialing in progresscalling after dialingringing incoming callcalled call in progress
tip (+)
ring (-)
Subscriber Line Interface
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Subscriber Line Interface
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Telephone Switching Network
Many local telephone exchanges had sprung up
Bell Telephone acquired them and interconnected them for long distance
LocalExchange Local
Exchange
LocalExchange
local loop
Long distancenetwork
trunkcircuit
subscriber line
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Class 3 Class 3
Class 2 Class 2
Class 1
Class 3
Regional centers
Sectional centers
Primary centers
Toll (tandem) offices
Central (end) offices
Class 4
last mile subscriber lineslocal loop
circuits,trunks
Class 5 switch is the sole interface to the subscriber lines
Class 5 Class 5 Class 5 Class 5 Class 5
Class 4 Class 4 Class 4
US Telephone Switching Network
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Pulse Dialing and Tone Dialing
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Multiplexing
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Time Division Multiplexing
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Switching Classes
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Class 5 to Class 4 Connection
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Mobile Communication
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Cellular ConceptThe core idea that led to today’s system was the cellular concept.
The cellular concept: multiple lower-power base stations that service mobile users within their coverage area and handoff users to neighboring base stations as users move. Together base stations tessellate the system coverage area.
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Cellular Concept
Thus, instead of one base station covering an entire city, the city was broken up into cells, or smaller coverage areas.
Each of these smaller coverage areas had its own lower-power base station.
User phones in one cell communicate with the base station in that cell.
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Circular Coverage AreasOriginal cellular system was developed assuming base station antennas are omnidirectional, i.e., they transmit in all directions equally. Users located outside
some distance to thebase station receive weak signals.
Result: base station hascircular coveragearea.
Weak signal
Strong sig
nal
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Multiple Antennas on Cell Towers
Cellular base station tower (antenna tower that cell phones “talk” to) use multiple antenna to improve the quality of voice signal received from cell phone users.
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A Handoff
At some point, the user’s signal is weak enough at B1 and strong enough at B2 for a handoff to occur.
Specifically, messages are exchanged between the user, B1, and B2 so that communication to/from the user is transferred from B1 to B2.
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Example of Frequency Reuse
Cells using the same frequencies
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Cellular Telephone – 2nd Generation
PCS – Personal Communication Systems –essentially all-digital cell phone service
PCS phones came in three technologies:TDMA – time division multiple access
CDMA – code division multiple access
GSM – global system for mobile communications
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Cellular Telephone – 2.5 Generation
AT&T Wireless, Cingular Wireless, and T-Mobile now using GPRS (General Packet Radio Service) in their GSM networks (can transmit data at 30 kbps to 40 kbps)
Verizon Wireless, Alltel, U.S.Cellular, and Sprint PCS are using CDMA2000 1xRTT (one carrier radio-transmission technology) (50 kbps to 75 kbps)
Nextel used IDEN technology
EDGE (Enhanced Data Rates for Global Evolution) replaces GSM and can transfer data at rates of 70 kbps to 135 kbps
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Cellular Telephone – 3rd Generation
UMTS (Universal Mobile Telecommunications System) – also called Wideband CDMA; the 3G version of GPRS; UMTS not backward compatible with GSM (thus requires phones with multiple decoders) (200 kbps to 300 kbps)
1XEV (1 x Enhanced Version) – The 3G replacement for 1xRTT; will come in two forms:
1xEV-DO for data only (400 kbps to 700 kbps)
1xEV-DV for data and voice
HSDPA (High Speed Downlink Packet Access) is an extension of the GSM/EDGE technology. Data rates 400 kbps to 700 kbps.
EV-DO Rev.A – speeds up to 3.1 Mbps
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3G Distribution Network
3G Distribution Network
What is Mobile Telephony (3G)?
•Direct to consumer service carried in-band over 3G mobile telephone networks, offering:•Recorded video-clips•Could provide ‘mobisodes’•Video messaging between handsets•Content can be FTV or pay-tv
3G cellular transceiver network
3G handset
ContentServer
MPEG4 Encoded Content
Cellular Telephone – 3rd Generation
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Cellular Telephone – 4th Generation
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The transfer of voice signals using a packet switched network and the IP protocol.
Voice over IP (VoIP) can be internal to a company (private VoIP) or can be external using the Internet.
VoIP consumes many resources and may not always work well, but can be cost effective in certain situations.
Three basic ways to make a telephone call using VoIP:
1. PC to PC using sound cards and headsets (or speakers and microphone)2. PC to telephone (need a gateway to convert IP addresses to telephone numbers)3. Telephone to telephone (need gateways)
Internet Telephony (Voice over IP)
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Simple Management Platform for Voice and Data
Centralized Maintenance, Upgrade and Operation
Manage Incoming Calls Easily (Detailed Call Log, Screen Pop)
Simple Outgoing Calls by Universal Directory Access (Phone Book)
Easy to Add or Relocate IP Phones
Internet Protocol (IP) Phone System
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Modem
For transfer information signals through telephone network
In a sender, modulation is a technique that enables information signals to be passed a telephone network, which superimpose the information signal on to a simple carrier signal in such a way that one or more components (amplitude, frequency, phase) of the carrier are modified to carry the information
In a receiver, reverse process called demodulation is carried out to retrieves back the information
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Amplitude Modulation
Modem
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Using modems to send and receive data
Sending site
Digital signal
Modem
Analog signal
Modem
Digital signal
Receiving site
Modem
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Used to shareUsed to share
Networks and the InternetA network is a collection of computers and devices connected together
ResourcesResources
Hardware devices
Hardware devices
Software programs
Software programs
DataData To save time and
money
To save time and
money
InformationInformation
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What is a Network?
A network is simply two or more computers that are linked together.The most common types of networks are:
Local Area Networks (LANS) and Wide Area Networks (WANS).
The primary difference between the two is that a LAN is generally confined to a limited geographical area, whereas a WAN covers a large geographical area. Most WANs are made up of several connected LANs.
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Computer Networks
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LAN (Local Area Network)A network of computers that are in the same physical location, such as home or building
Usually connected using EthernetA standard on how computers communicate over a shared media (cable)
Old: BNC connector for coaxial cable New: RJ45 for twisted pair cable
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Isolating Traffic Patterns with Switches
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WLAN (Wireless LAN)
Wi-Fi (Wireless Fidelity)A wireless technology that connects computers without cables
Access Point (AP)A device (base station) that connects wireless devices togetherUsually connected to a wired-network
ESSID (Extended Service Set ID)A “name” for the AP, eg. mobilenet
HotspotThe area covered by wireless access points
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Wireless LAN
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Wireless LAN
Approved 2007, 540Mb/s
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Router
Routers connect two or more networks and forward data packets between them. When data arrives from one of the segments, the router decides, according to it's routing table, to which segment to forward that data.
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LAN to WAN connection
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Networks and the Internet
Worldwide collection of networks that connects millions of businesses, government agencies, educational institutions, and individuals
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the Internet is a vast, international network of computersthe physical connections between computers vary, but the overall effect is that computers around the world can communicate and share resources
the Internet traces its roots back to 1969, when the U.S. government sponsored the first long-distance computer networkstarting with only 4 computers, the network would eventually evolve into today's Internet
the World Wide Web is a collection of software that spans the Internet and enables the interlinking of documents and resources
the basic idea for the Web was proposed by Tim Berners-Lee in 1989his system interlinked documents (including multimedia elements such as images and sound clips) over the Internetthrough the use of well-defined rules, or protocols, that define how they are formatted, documents could be shared across networks on various types of computers
Networks and the Internet
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What is the Web?
A Web site is a collection of
related Web pages
A Web site is a collection of
related Web pages
A Web page contains text, graphics, audio, video, and links to other Web pages
A Web page contains text, graphics, audio, video, and links to other Web pages
You can share information on a socialnetworking Web site
You can share information on a socialnetworking Web site
Billions of documents, called Web pages, available to anyone connected to the Internet
A blog consists of time-stamped articles in
a journal format
A blog consists of time-stamped articles in
a journal format
A podcast is recorded audio
stored on a Web sitethat can be
downloaded
A podcast is recorded audio
stored on a Web sitethat can be
downloaded
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Viewing a Web Pagea Web page is a text document that contains additional formatting information in a language called HTML (HyperText Markup Language)
a Web browser is a program that accesses a Web page, interprets its content, and displays the page
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Web Addressesa Web server is an Internet-enabled computer that stores Web pages and executes software for providing access to the pages
when you request a Web page, the browser sends a request over the Internet to the appropriate serverthe server locates the specified page and sends it back to your computer
Web pages require uniform names to locate and identify them uniquelyeach page is assigned a Uniform Resource Locator (URL) URL's are commonly referred to as Web addressesthe different parts of the Web address provide information for locating the page
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Internet ≠ World Wide Web
the Internet could exist without the Web and did, in fact, for many years (applications included email and news groups)
the Web couldn't exist without the Internetthe Internet is the hardware that stores and executes the Web software
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Internet Service Provider (ISP)
An ISP is a company that maintains Internet computers and telecommunications equipment in order to provide Internet access to businesses, organizations and individuals
User ID and password required
Email account monthly fee
May have local access telephone numbers
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Dial-up Services
ModemModulator/demodulator
A device that converts analog signal to digital (modulation) and vice versa (demodulation)
Speed1200/2400/9600 bps
14.4/28.8/33.6 Kbps
56 Kbps
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Digital subscriber line (DSL) is a relative newcomer to the field of leased line services.
DSL can provide very high data transfer rates over standard telephone lines.
DSL, depending on the type of service, is capable of transmission speeds from 100s of kilobits into single-digit megabits.
Because DSL is highly dependent upon noise levels, a subscriber cannot be any more than 5.5 kilometers (2-3 miles) from the DSL central office.
A DSL service can be symmetric, in which the downstream and upstream speeds are identical, or asymmetric in which the downstream speed is faster than the upstream speed.
Digital Subscriber Line
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A DSL service often connects a user to the Internet.
A DSL service can also provide a regular telephone service.
The DSL provider uses a DSL access multiplexer (DSLAM) to split off the individual DSL lines into homes and businesses.
A user than needs a splitter to separate the telephone line from the DSL line, and then a DSL modem to convert the DSL signals into a form recognized by the computer.
Digital Subscriber Line
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Splitter for DSL
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Digital Subscriber Line
Cable modems allow high speed access to wide area networks such as the Internet.
Most cable modems are external devices that connect to the personal computer through a common Ethernet card.
Cable modems can provide data transfer speeds between 500kbps and 2.5Mbps
Cable Modems
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Home Network (single machine)
USB/Ethernet Cable
DSL/Cable Modem
Wall Jack
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Home Network (multiple machines)
Ethernet Cable
DSL/Cable Modem
Wall Jack
Hub/Switch/Router
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Home Wireless Network
Ethernet Cable
DSL/Cable Modem
Wall Jack
Hub/Switch/Router
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Home Wireless Network