Telephone - Hong Kong Polytechnic Universitylnx01.ee.polyu.edu.hk/~eewlchan/EE1D01/EE1D01_2c.pdf · Class 5 Class 5 Class 5 Class 5 Class 5 Class 4 Class 4 Class 4 US Telephone Switching

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


28Frequency ModulationPhase Modulation

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.



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Splitter for DSL


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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

Documents

Telephone - Hong Kong Polytechnic Universitylnx01.ee.polyu.edu.hk/~eewlchan/EE1D01/EE1D01_2c.pdf · Class 5 Class 5 Class 5 Class 5 Class 5 Class 4 Class 4 Class 4 US Telephone Switching