Telecommunication Systems Spring 2010

Telecommunication Systems Spring 2010

DSL What is DSL (Digital Subscriber Line)? • A broadband access technology • An uninterrupted high speed internet connection • One can use applications that need higher speeds, even if high performance (fiber) cable networks are not available • Examples include Video-on-demand, Online education etc. • A DSL connection can eliminate the frustrating delays associated when waiting to download information and graphics from the Internet • A DSL connection is always-on-line (like a LAN connection) with no waiting time for dialing or connecting • DSL provides higher transmission rates on existing twisted pair copper loop (from customer to the exchange) • In other words, DSL is used to obtain more bandwidth over existing copper telephone cabling

Splitter DSL Modem DSL DSL Network Architecture • Customer Premises Equipment (CPE)

DSL DSL Network Architecture • Customer Premises Equipment (CPE) • DSL Modem • Both internal and external modems are there

DSL DSL Network Architecture • Customer Premises Equipment (CPE) • DSL Modem working principle • To create multiple channels, ADSL modems divide the available bandwidth of a telephone line in one of two ways: Frequency-division multiplexing (FDM) or echo cancellation • FDM assigns one band for upstream data and another band for downstream data. The downstream path is then may be divided by time-division multiplexing into one or more high-speed channels and one or more low-speed channels. The upstream path may also be divided into corresponding low-speed channels • Echo cancellation assigns the upstream band to overlap the downstream, and separates the two by means of local echo cancellation

DSL DSL Network Architecture • Customer Premises Equipment (CPE) • DSL Modem working principle • Echo cancellation assigns the upstream band to overlap the downstream, and separates the two by means of local echo cancellation • With either technique, DSL splits off a 4-kHz region for basic telephone service.

DSL • DSL utilizes frequencies above 4,000 Hertz • The use of higher frequencies to support higher speed services also results in shorter loop reach • This is because high frequency signals transmitted over copper loops attenuate energy faster than the lower frequency signals • CAP (Carrierless Amplitude Phase) Modulation and DMT (Discrete Multi-tone) Modulation use a lower range of frequency spectrum than earlier alternative line coding techniques • They have reduced signal attenuation and enabled desired loop reach to be achieved

DSL • That's why CAP and DMT have become the most popular line coding techniques to be used to support DSL technology • CAP treats the entire frequency spectrum as a single channel and optimizes the data rate while DMT divides it into 256 sub-channels and optimizes the data rate for each sub-channel and each sub-channel is then modulated with QAM 64 • CAP is a single-carrier modulation technique and is susceptible to narrowband interference • DMT uses multiple carriers • DMT is capable of more speed than CAP • CAP has been tested longer than DMT, but DMT has been accepted as the standard by ANSI and ETSI

DSL • Splitters

DSL DSL Network Architecture • Customer Premises Equipment (CPE) • The Splitter • Splitters/Micro-filters are used to separate the two different frequency bands used over the telephone line (voice and data) • Splitters prevent the analogue devices from interfering with the broadband frequency ranges used by DSL modem

DSL DSL Network Architecture • Customer Premises Equipment • DSL Ethernet Modem

DSL DSL Network Architecture • Exchange Side

DSL • Patch Pannels and DSLAM

DSL What is xDSL? • xDSL is a generic abbreviation for a number of DSL variations/flavors • The different variations of DSL technology have been implemented to meet the specific needs of any home users, small and medium size businesses, schools and colleges, and corporate sectors • What is Asymmetric DSL or ADSL? • Higher downstream rate compared to upstream rate • Applications include web-browsing, video downloads etc. • What is SDSL? • Symmetric Digital Subscriber Line • It is symmetrical (an equal amount of bandwidth is available on the upstream and the downstream)

DSL • What is RA-DSL? • Rate Adaptive Digital Subscriber Line (R-ADSL) technology can automatically adjust the speed of the line by conducting a series of initial tests to determine the maximum speed possible on a particular line • In areas where there is a large variance in the length of the local loop (distance between the service user and the central office), the gauge of the wire, and the condition of the line, it becomes difficult to determine what speeds should be provisioned over each line • Weather condition further acts to change the maximum possible throughput on a given line

DSL • What is VDSL? • Very High Bit-rate Digital Subscriber Line provides provision for shorter local loops, perhaps up to 4,000ft with downstream speeds of up to a 52 Mbps • VDSL comes in two variants, a "symmetrical" and an "asymmetrical" version • What is IDSL? • ISDN Digital Subscriber Line (IDSL) permits data transmission at speeds of 128 Kbps over a single copper pair specifying loops up to 18,000 feet • Because IDSL uses the same industry-standard line coding technique as ISDN, customers with ISDN BRI terminal adapters can use their current TAs/ routers for connecting to IDSL lines • ISDN can be used for data-only applications

DSL • What is M-SDSL? • Multirate Symmetrical Digital Subscriber Line • M-SDSL can automatically adjust the speed of the line • It supports eight distinct rates and permits data transmission speeds between 64 Kbps and 128 Kbps specifying loops up to 29,000 ft and stepping down to 15,000 ft at a full 2 Mbps rate • M-SDSL uses Carrierless Amplitude Phase modulation (CAP) modulation

DSL • Summary of different variations of DSL

DSL-Review • Which of the following statements about DSL is not true? • DSL is a broadband access technology • DSL provides high speed internet connection • It is an “always-on” connection • A DSL connection can eliminate the frustrating delays associated when waiting to download information and graphics from the Internet • A DSL line can support only one telephone number • DSL increases the download times

DSL-Review • What are the two line coding schemes used in the DSL technology? CAP DMT • Which of the following line coding scheme has been adapted as standard by the ANSI and ETSI? CAP DMT • In the DSL terms, what does CAP stand for? • Carrier Amplitude Phase Modulation

DSL-Review • Which of the following statements about CAP (Carrierless Amplitude Phase Modulation) is not true? • CAP enables the use of lower range of frequency spectrum • SDSL used CAP line coding • RA-DSL uses the CAP line coding • MSDSL uses CAP • CAP treats the entire frequency spectrum as a single channel • CAP is immune to narrow-band interference

DSL-Review • High frequency signals transmitted over copper loops attenuate energy faster than the lower frequency signals TRUE FALSE • Why CAP and DMT have become the most popular line coding techniques to be used to support DSL technology? • They have reduced signal attenuation by using a lower range of frequency spectrum than earlier alternative line coding techniques

DSL-Review • Why DMT is a better choice than CAP? • Speed • Bandwidth efficiency • Immunity to interference • Power consumption • What is DMT? • Discrete Multi Tone modulation • Where is DSLAM located? • Customer Premises • Exchange side

DSL-Review • A DSLAM, receives signals from multiple customer Digital Subscriber Line (DSL) connections and puts the signals on a high-speed backbone line using multiplexing techniques TRUE FALSE • At the other end of each transmission DSLAM demultiplexes the signals and forwards them to appropriate individual DSL connections TRUE FALSE

DSL-Review • A modulation technique and is susceptible to narrowband interference • CAP • DMT • Each of the sub bands can support QAM-64 modulation • DMT • CAP

Thank You 27

Telecommunication Systems Spring 2010