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Residential Broadband

Residential Broadband. Jacek Ilow Dalhousie University. Why High Speed Access?. Broadband Services large data files real time applications multimedia WWW Quality of Service bandwidth, end-to-end delay, loss of infromation Broadband Services to home. The Last Mile.

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Residential Broadband

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  1. Residential Broadband Jacek Ilow Dalhousie University Residential Broadband

  2. Why High Speed Access? • Broadband Services • large data files • real time applications • multimedia • WWW • Quality of Service • bandwidth, end-to-end delay, loss of infromation • Broadband Services to home Residential Broadband

  3. The Last Mile • High bandwidth demand • Best use of existing coper • Traditional telephone services without interruption • Minimal line engineering and testing installation • Off-load network switches Residential Broadband

  4. Copper Cable • Collective assets of millions of dollars • Central Office- home interconnection by copper twisted pair local loop telephone lines • T1/E1 lines from the backbone between Cos • Early 1980’s T1/E1 migrate to local loop • expensive to install, reconfigure and maintain Residential Broadband

  5. The x in DSL • Copper Access Technologies • voice band modems (V.22, V.32, V.34), xDSL • DSL: Digital Subscriber Line • refers to a modem not the line (Belcore) • transmission scheme designed for high speed data networking over twisted pair • xDSL: wide variation of DSL technologies • ADSL, VDSL, HDSL, SDSL, BDSL Residential Broadband

  6. Digital Subscriber Line • Modem used for basic rate ISDN (128kbps) • Characteristics • duplex transmission, 160kbps, 18,000 feet, 24 gauge wire multiplexing • demultiplexing into two B channels (64kbps each), one D channel (16 kbps) plus overhead • Twisted-pair bandwidth 0-80kHz • Simultaneously provisioning of analog POTS - Plain Old Telephone System Residential Broadband

  7. High Speed DSL • Introduced in late 1980’s (Bellcore) • Reliable cost effective, provision of repear free T1/E1(1.544 / 2.048 Mbps) service • HDSL creates mathematical model of copper wire, allowing the transmission device to compensate for copper-base distortions • Immune to cross-talk, quality comparable to fibre optics, BER=10E-10+ Residential Broadband

  8. Wavelet DSL • Symmetric DSL • Supports one or two pair lines • Supports 1-4 Mbps, 12,000-18,000 feet • Uses Discrete Wavelet Multi-tone Technology • dynamic bandwidth access • immunity to narrow-band impulse noise • simple instalation of line cards • no interference with other equipment Residential Broadband

  9. Single Line DSL • Symmetric data rates over a single twisted pair • Reliable, cost effective, provision of repeatless T1/E1 (1.544/2.048 Mbps) services • Duplex, no line conditioning • Advantages of HDSL, plus lower equipment and installation cost • one transceiver instead of two Residential Broadband

  10. VDSL/VASDL • Introduced in mid-1995 • Designed to work in conjuction with fiber to the curb (FTC) • Provides higher rates • 51-55 Mbps upstream, 1000 feet • 26.6-27.6 Mbps, 3000-4000 feet • 12.96-13.8 Mbps, 4500 feet • 13 Mbps upstream • Lower cost than ADSL Residential Broadband

  11. VDSL • Still in definition state • preliminary products exist • little known about line characteristics, RFI emission for the used frequency • Forward error control and interleaving • Multiplexing of data stream • Services environment: ATM, other traffic format • Integration with existing modem technologies Residential Broadband

  12. Rate Adaptive DSL • Rate adaptive based on • line length • transmission quality • Selects the higher operational speed automatically • Downstream 640 kbps-7.168Mbps, Upstream 90.6kbps-1.008Mbps • Reliable, less complex than ADSL Residential Broadband

  13. Cable Modem • What is cable modem? • Device that provides high speed data transfer via cable TV networks • External device connected to the PC via a 10BASE-T Ethernet • How fast is cable modem? • Speeds vary widely based on cable modem system, cable network architecture, traffic load • downstream up to 27 Mbps aggregated (1-5Mbps) • upstream up to 10Mbps (500kbps-2.5Mbps) Residential Broadband

  14. How Does it Work? • Modulates/Demodulates digital signals • More complicated than dial-in modem • Part modem, tuner, encryption/decryption device, router, network interface, SNMP agent, Ethernet hub • Downstream modulated digital data on a 6MHz TV channel • 50-450 KHz, coaxial cable • up to 750 MHz, hybrid fiber coax • Upstream 5-42 MHz Residential Broadband

  15. Modulation Schems • Upstream • QPSK (up to ~10Mbps) • 64 QAM (up to ~30Mbps) • no interference with TV signal • Downstream, reverse channel • 5-42 MHz • QPSK or similar to reduce interference effects • QPSK more robust but slower than QAM Residential Broadband

  16. ADSL Technology Description • It uses state of the art technology in more then one area. • Challenges • Full use of the copper line frequency spectrum (1.1Mhz) . • An advanced coding/decoding method. • Ability to work simultaneously with POTS on the same copper line. Residential Broadband

  17. Discrete MultiTone • The lower 4Khz are being used by the POTS. • The amplification isn't the same in all frequencies. • DMT divides the frequency rang to 256 sub-frequencies from 64Khz to 1.1Mhz Each subferqency is an independent channel and has it own stream of signals . The ADSL protocol defines a basic stream of data which is known to both endpoints in advanced and enables them to find the specific SNR for each sub-frequency , and uses this information to split the data over the sub-frequencies Residential Broadband

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  21. Error Correction Coding • Constellation encoding and decoding the information on the line can be damaged and yet the decoder rebuild the information in a very high reliability. • To improve the performance of ADSL system some companies use 16 state 4 dimensional trellis code on top of the constellation encoding. • Another useful method to increase the ADSL systems reliability is Forward Error Correction (FEC) , which is based on Reed Solomon coding method . Residential Broadband

  22. Framing and Scrambling • DSL uses a specific framing method . • The main frame is called Superframe and it is composed of 68 ADSL data frames , • the ATU-C sends a superframe every 17 msec . • Each data frame gets his information from two data buffers (interleaved buffer and fast buffer) which are scrambled at a specific sequence , this scrambling method makes the error correction and coding more efficient. Residential Broadband

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  24. Summary • The end-user does not really care which technology is used: he is looking at the bottom line, that is how much he will have to pay and whether what he pays is worth paying for. • Solution: • offer the subscriber connectivity at varying costs and QoS Residential Broadband

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