COMPUTER NETWORKING 2 LECTURE 3: BROADBAND TECHNOLOGY & DSL

o CONTENTS I. INTRODUCTION II. (POST) DIAL-UP MODEMS III. INTEGRATED SERVICE DIGTAL NETWORK (ISDN) IV. CABLE MODEM V. DSL VI. STAELLITES TECHNOLOGY VII. CELLUULAR COMMUNCATION TECHONOLOGY

Introduction The 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 Technology Introduction 1. Broadband Technology A kind of wide-spread, high-speed Internet access 2. Broadband Connections Cable model, DSL (ADSL, SDSL), T1& ISDN, and Satellite

5 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 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 Data D Channel Kbps B Channels 64 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

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. ADSL ADSL Lite HDSL SDSL VDSL 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

22 : 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

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