Introduction to Digital Subscriber Line (DSL)

EE4220 Communications systemDr. Hassan YousifElectrical Engineering DepartmentCollege of EngineeringSalman Bin Abdulaziz University

Lect no-5

18 - 2

Digital Subscriber Line (DSL) Broadband Access

Customer Premises

downstream

upstreamVoiceSwitch

Central Office

DSLAM

DSL modem

DSL modem

LPFLPF

Internet

DSLAM - Digital Subscriber Line Access Multiplexer

LPF – Low Pass Filter (passes voiceband frequencies)

Telephone Network

Introduction

DSL FlavorsDSL is often called xDSL

since there are many varieties (different x)

e.g. ADSL, HDSL, SHDSL, VDSL, IDSL, etc.

There were once many unconnected typesbut now we divide them into three main families

The differentiation is by means of the application scenario

• HDSL (high bit rate, mainly business, data + telephony)

• ADSL (asymmetric, mainly residential, Internet access)

• VDSL (very high rate, but short distance)

More xDSL flavors

modem speed reach main applications

IDSL 160 (144) Kbps 5.5 km POTS replacement, videoconferencing, Internet access

HDSL 2 Mbps (4-6W) 3.6-4.5 km T1/E1 replacement PBX interconnect, FR

HDSL2 2 Mbps (2W) 3 km same as HDSL

SHDSL 2.3 Mbps 3 km same as HDSL

SHDSLbis 4.6 Mbps 3 km same as HDSL

More xDSL flavors (cont.)

modem speed reach main applications

ADSL 6 Mbps DS 640 Kbps US

3.5-5.5 km residential Internet, video-on-demand

ADSL2 8 Mbps DS 800 Kbps US

> ADSL Internet access, VoIP

ADSL2+ 16 Mbps DS 800 Kbps US

< 2 km “

VDSL <= 52 Mbps 300m - 1 km LAN interconnect, HDTV, combined services

VDSL2 200 Mbps (aggregate)

up to 1.8 km “

cable modem 10-30Mbps DS shared

50 km residential Internet

HPNA 1, 10 Mbps home wiring residential networking

Not DSL

History of wireless communication

• Guglielmo Marconi invented the wireless telegraph in 1896• Communication by encoding alphanumeric characters in analog

signal• Sent telegraphic signals across the Atlantic Ocean

• 1914 – first voice communication over radio waves• Communications satellites launched in 1960s• Advances in wireless technology

• Radio, television, mobile telephone, communication satellites

• More recently• Satellite communications, wireless networking, cellular technology

What is Wireless Communication ?

• Transmitting voice and data using electromagnetic waves in open space (atmosphere)

• Electromagnetic waves • Travel at speed of light (c = 3x108 m/s)

• Has a frequency (f) and wavelength ()• c = f x

• Higher frequency means higher energy photons

• The higher the energy photon the more penetrating is the radiation

Types of wireless communication

celullar wireless computer network radio service

Electromagnetic radiation spectrum

Wavelength of Some Technologies

• GSM Phones: • frequency ~= 900 Mhz

• wavelength ~= 33cm

• PCS Phones• frequency ~= 1.8 Ghz

• wavelength ~= 17.5 cm

• Bluetooth: • frequency ~= 2.4Gz

• wavelength ~= 12.5cm

Types of electromagnetic carriers

• when the distance between the sender and receiver is short (e.g. TV box and a remote control) infrared waves are used

• for long range distances between sender and receiver (e.g. TV broadcasting and cellular service) both microwaves and radio waves are used• radio waves are ideal when large areas need to be coverd and

obstacles exist in the transmission path

• microwaves are good when large areas need to be coverd and no obstacles exist in the transmission path

Wireless applications (services)

Advantages and disadvantages of wireless communication

• advantages:• mobility

• a wireless communication network is a solution in areas where cables are impossible to install (e.g. hazardous areas, long distances etc.)

• easier to maintain

• disadvantages:• has security vulnerabilities

• high costs for setting the infrastructure

• unlike wired comm., wireless comm. is influenced by physical obstructions, climatic conditions, interference from other wireless devices

Frequency Carries/Channels

• The information from sender to receiver is carrier over a well defined frequency band.

• This is called a channel

• Each channel has a fixed frequency bandwidth (in KHz) and Capacity (bit-rate)

• Different frequency bands (channels) can be used to transmit information in parallel and independently.

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Wireless System Architecture

HostAccessPoint

WirelessBar codeScanner

2.- Database system3.- Graphic User Interface

1.- Client Application

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Evolution of Wireless Technology

• Nikola Tesla• Invented radio communications

• Guglielmo Marconi• Sent telegraphic signals across the Atlantic Ocean

• Communications satellites launched in 1960s• Advances in wireless technology

• Radio, television, mobile telephone, communication satellites• More recently

• Satellite communications, wireless networking, cellular technology

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Broadband Wireless Technology

• Higher data rates achievable with broadband wireless technology• Graphics, video, audio

• Shares same advantages of all wireless services

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Wireless Technologies

• Unlicensed Frequency Spectrum• Industrial, Scientific and Medical (ISM)

• 915 MHz• 2.45 GHz• 5.8 GHz

• Wireless Fidelity (Wi-Fi)• Based on IEEE 802.11 standards• Refers to 802.11-compatible products certified as

interoperable by the Wi-Fi Alliance• Covers office and home based LANs as well as hotspots

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Comparison of Wi-Fi Standards

IEEE Standard

Data Rate Frequency Band

Notes

802.11 1 Mbps2 Mbps

2.4 GHz First standard (1997). Used both DSSS & FHSS.

802.11a Up to 54 Mbps

5 GHz Second standard (1999). Products not released until late 2000.

802.11b 5.5 Mbps11 Mbps

2.4 GHz Third standard but second wave of products (1999). Most common.

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Comparison of Wi-Fi Standards

IEEE Standard

Data Rate Frequency Band

Notes

802.11g Up to 54 Mbps

2.4 GHz Standard approved in June 2003.

802.11n Up to 600 MbpsMIMO (multiple input multiple output)

5 GHz and/or 2.4 GHz

Released in 2008. Full approval expected in December 2009.

Next generation?

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Wireless Technologies (cont.)

• Unlicensed Frequency Spectrum• Unlicensed National Information Infrastructure (U-

NII)• U-NII devices do not require licensing• Designated to provide short-range, high-speed wireless

networking communication at low cost• Three frequency bands (100 MHz each) were set aside by the

FCC in 1997• Objective was to help schools connect to the Internet without

the need for hard wiring

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Wireless Technologies (cont.)

• Unlicensed Frequency Spectrum• Unlicensed National Information Infrastructure (U-

NII)

Designation

Frequency Band

Maximum Output Power

Use

U-NII-1 5.15 – 5.25GHz 50 mW Indoor only

U-NII-2 5.25 – 5.35 GHz 250 mW Outdoor and indoor

U-NII-2e* 5.47 – 5.725 GHz 250 mW Outdoor and indoor

U-NII-3 5.725 – 5.825 GHz 1 W Outdoor only

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Wireless Technologies (cont.)

• Worldwide Interoperability for Microwave Access (WiMAX)

• Similar to Wi-Fi

• Range of 40-50 Km• Wireless alternative to cable, DSL, and T1/E1 for last-mile broadband

access

• Initial developments were in fixed locations but a mobile version was also developed

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Wireless Technologies (cont.)

• ZigBee• Standard ratified on Dec 9, 2004• Enables reliable, cost-effective, low-power, wirelessly

networked, monitoring and control products based on an open global standard

• Targeted to sensors and control devices that do not require high bandwidths but do require low latency and very low power consumption

• Initial markets• Home control• Building Automation• Industrial Automation

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Wireless Technologies (cont.)

• Ultrawideband• According to the FCC, ultrawideband is any radio technology with

a spectrum that occupies greater than 20% of the center frequency or a minimum of 500MHz

• An UWB system provides a wireless PAN• Data payload communication capabilities of 53.3, 80, 110, 160, 200,

320, 400, and 480 Mb/s

• Employs orthogonal frequency division multiplexing (OFDM)

• Technology specification developed by MultiBand OFDM Alliance (MBOA)

• Over 170 member companies

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Limitations and Difficulties

• Limitations as well as political and technical difficulties inhibit wireless technologies

• Lack of an industry-wide standard• Device limitations

• Small LCD on a mobile telephone can only display a few lines of text

• Browsers of most mobile wireless devices use wireless markup language (WML) instead of HTML

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Standards Organizations

• National Technical Standard-Setting Organizations: • American National Standards Institute

• Institute of Electrical and Electronic Engineers, Inc

• National Institute of Standards and Technology

• International Standard-Setting Organizations: • International Telecommunication Union

• International Standards Organization

• European Telecommunications Standards Institute

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Wireless Technology & Governance

• Federal Communications Commission • National Telecommunications and Information

Administration • Cellular Telecommunications Industry Association