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DIGITAL SUBSCRIBER LINE

DIGITAL SUBSCRIBER LINE. DSL BLOCK DIAGRAM. Asymmetrical DSL (ADSL). ADSL divides up the available frequencies in a line on the assumption that most Internet users look at, or download, much more information than they send, or upload.

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DIGITAL SUBSCRIBER LINE

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  1. DIGITAL SUBSCRIBER LINE

  2. DSL BLOCK DIAGRAM

  3. Asymmetrical DSL (ADSL) • ADSL divides up the available frequencies in a line on the assumption that most Internet users look at, or download, much more information than they send, or upload. • Under this assumption, if the connection speed from the Internet to the user is three to four times faster than the connection from the user back to the Internet, then the user will see the most benefit (most of the time).

  4. Asymmetrical DSL (ADSL) • ADSL is an adaptive technology. • The system uses a data rate based on the condition of the local loop line. • Speed: Most existing local loops can handle bandwidths up to 1.1 MHz.

  5. ADSL Modem

  6. Two standards for ADSL • Discrete multitone (DMT) • Carrierless amplitude/phase (CAP)

  7. CAP - three distinct bands: • Voice channel - 0 to 4 KHz • Upstream channel - 25 and 160 KHz • Downstream channel - 1.5 MHz

  8. Carrierless amplitude/phase (CAP) • Advantage: Minimizes the possibility of interference between the channels on one line, or between the signals on different lines

  9. Discrete multitone (DMT) • Constantly shifts signals between different channels, searching for the best channels for transmission and reception

  10. Discrete multitone (DMT)

  11. Asymmetrical DSL (ADSL) • ADSL is an asymmetric communication technology designed for residential users; it is not suitable for businesses.

  12. 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

  13. OTHER TYPES OF DSL: • Symmetric DSL (SDSL) • High-bit-rate DSL (HDSL) • Very high bit-rate DSL (VDSL)

  14. Symmetric DSL (SDSL) • Used mainly by small businesses & residential areas • Bit rate of downstream is higher than upstream

  15. High-bit-rate DSL (HDSL) • Used as alternative of T-1 line • Uses 2B1Q encoding • Less susceptible to attenuation at higher frequencies • Unlike T-1 line (AMI/1.544Mbps/1km), it can reach 2Mbps @ 3.6Km

  16. Very high bit-rate DSL (VDSL) • Uses DMT modulation technique • Effective only for short distances(300-1800m) • Speed: downstream : 50 - 55 Mbps upstream : 1.5-2.5 Mbps

  17. Question! • Distance is a limitation for DSL, why it's not also a limitation for voice telephone calls ?

  18. Answer! • The answer lies in small amplifiers called loading coils that the telephone company uses to boost voice signals • these loading coils are incompatible with ADSL signals, so a voice coil in the loop between your telephone and the telephone company's central office will disqualify you from receiving ADSL.

  19. ADSL :customer disqualifying factors • Bridge taps - These are extensions, between you and the central office, that extend service to other customers. While you wouldn't notice these bridge taps in normal phone service, they may take the total length of the circuit beyond the distance limits of the service provider. • Fiber-optic cables - ADSL signals can't pass through the conversion from analog to digital and back to analog that occurs if a portion of your telephone circuit comes through fiber-optic cables. • Distance - Even if you know where your central office is (don't be surprised if you don't -- the telephone companies don't advertise their locations), looking at a map is no indication of the distance a signal must travel between your house and the office.

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