COMPUTER NETWORKING 2

LECTURE 3: BROADBAND TECHNOLOGY& DSL

oCONTENTSI. INTRODUCTIONII. (POST) DIAL-UP MODEMSIII. INTEGRATED SERVICE DIGTAL NETWORK (ISDN)IV. CABLE MODEMV. DSLVI. STAELLITES TECHNOLOGYVII. CELLUULAR COMMUNCATION TECHONOLOGY

IntroductionThe public switched telephone system is the largest

and most important communication system in the world

Public refers to the idea that anyone can connect to it; switched indicates that anyone can connect to anyone else

Though originally designed for voice communications, telephone networks have been adapted to serve data communications, facsimile, and video

Broadband TechnologyIntroduction

1. Broadband Technology A kind of wide-spread, high-speed

Internet access

2. Broadband Connections Cable model, DSL (ADSL, SDSL), T1&

ISDN, and Satellite

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Narrowband vs Broadband

The Local Loop Ordinary telephone systems are often referred to

as POTS (plain old telephone service) Normally, each subscriber is connected to the

central office by a single twisted pair of wires The wires are twisted to reduce crosstalk Future developments include the inclusion of

fiber-optic connections direct to the subscriber for greater bandwidth

Local loop describes the physical connection between a telephone company Central Office (CO) and a subscriber consists of twisted pair and dialup call with

4 KHz of bandwidth It often has much higher bandwidth; a

subscriber close to a CO may be able to handle frequencies above 1 MHz

Figure 15-2

WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998

Voice over Analog Network

Figure 15-3

WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998

Voice and Data over Analog Network

CHAPTER

Digital Lines and the Integrated Service Digital Network (ISDN)

ISDN Defined Known as the Integrated Services Digital

Network Data, audio, image and video transmission

It is a switched digital telecommunication line that can be delivered over regular copper wires Possible to provide end-to-end digital

communications

Integrated Services Digital Network (ISDN) ISDN is designed to allow voice and data to be

transmitted along the same lines ISDN provides a way to standardize data and voice

communications without resorting to modems ISDN connects at a primary access point with a data

rate of 1.544 Mb/s One of these channels is the D (data) channel and is

used for setting up and monitoring calls The other 23 channels are called B (bearer) channels

and can be used for voice or data

Figure 15-4

WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998

Analog and Digital Services

Figure 15-5

WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998

Integrated Digital Network

Figure 15-6

WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998

Integrated Services Digital Network

ISDN Application Examples On/off ramp to the information super-

highway to communicate at speeds of 128 Kbps for a single ISDN line Multiple ISDN lines can be combined together

to achieve higher communication speeds Home use

On/Off ramp to the Internet Business world

Provide remote access to LANs .

ISDN Connections Can be obtained from a local telephone

company in the same way an analog connection is obtained

Phone companies offer different types of ISDN connections

ISDN Basic Characteristics

Signaling

DataDataData

D Channel16-64 Kbps

B Channels64 Kbps

Asymmetrical Digital Subscriber Line (ADSL) ADSL lines use the

frequencies above the voice range for high-speed data while leaving the use of the local loop for analog telephony intact

Typical ADSL uses include Internet access and interactive television

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9-3 DIGITAL SUBSCRIBER LINE

After traditional modems reached their peak data rate, telephone companies developed another technology, DSL, to provide higher-speed access to the Internet. Digital subscriber line (DSL) technology is one of the most promising for supporting high-speed digital

communication over the existing local loops .

ADSLADSL Lite

HDSLSDSLVDSL

Topics discussed in this section:

Introduction ADSL is a form of DSL, a data communications

technology that enables faster data transmission over copper telephone lines

ADSL is capable of providing up to 50 Mbps, and supports voice, video and data.

ADSL is the #1 Broadband Choice in the World with over 60% market share

ADSL is now available in every region of the world

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:Upstream and Downstream How is access technology designed? Most Internet users follow an asymmetric

pattern a subscriber receives more data from the

Internet than sending a browser sends a URL that comprises a few bytes in response, a web server sends content

Upstream to refer to data traveling from a subscriber to an ISP

Downstream to refer to data traveling from an ISP in the Internet to a subscriber

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12.5 Digital Subscriber Line (DSL) Technologies

ADSL is the most widely deployed variant and the one that most residential customers use

ADSL uses FDM to divide the bandwidth of the local loop into three regions one of the regions corresponds to traditional analog phone

service, which is known as Plain Old Telephone Service (POTS) and two regions provide data communication

Figure 12.5 (below) illustrates how ADSL divides bandwidth

What does ADSL mean

Asymmetric - The data can flow faster in one direction than the other. Data transmission has faster downstream to the subscriber than upstream

Digital - No type of communication is transferred in an analog method. All data is purely digital, and only at the end, modulated to be carried over the line.

Subscriber Line - The data is carried over a single twisted pair copper loop to the subscriber premises

ADSL Loop Architecture

ISP

Central Office

Subscriber premises

Voice Switch

DSL

ADSL Requirements

Phone-line, activated by your phone company for ADSL

Filter to separate the phone signal from the Internet signal

ADSL modem

Subscription with an ISP supporting ADSL

ADSL network components

The modem of the central office (ATU-C)

DSL access multiplexer (DSLAM)

Broadband Access Server (BAS)

Splitter - an electronic low pass filter that separates the analogue voice or ISDN signal from ADSL data frequencies DSLAM.

Advantages Connectivity – always connected Ease of use Reliability Security Speed

ADSL Modem

Distance Limitations ADSL is a distance-sensitive

technology The limit for ADSL service is 18,000 feet

(5,460 meters) At the extremes of the distance limits,

ADSL customers may see speeds far below the promised maximums

customers nearer the central office have faster connections and may see extremely high speeds