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    Broadband Access Networks

    Chapter 2

    Twisted-Pair based Access Networks

    Byeong Gi Lee

    Seoul National University

    EE4541.759 Spring 2006

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    BGL 2

    2. TP-based Access Network

    Limitation of POTS and ISDN

    Digital Loop Carrier

    DSL TechnologiesIDSL, HDSL, SDSL,

    ADSL, G.Lite, VDSL, and Comparisons ADSL Access Network, Architecture,

    Components, and Protocol Model

    Spectrum Allocations Modulation Techniques

    Applications, Challenges, and Penetration

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    BGL 3

    Structure of Access NetworkADSL: Asymmetric Digital Subscriber Line

    DBS: Direct Broadcast SatelliteDMB: Digital Multimedia Broadcast

    FTTC: Fiber To The Curb

    HFC : Hybrid Fiber Coaxial

    LMDS: Local Multipoint Distribution System

    MMDS: Multi-channel Multipoint Distribution System

    MSO: Multiple Service Operator

    Digital DBS

    DMB

    HFC

    FTTC/FTTO

    ISDN Line (DSL)

    VDSL Modem

    ADSL Modem

    Cable Modem

    Analog

    Modem

    ISDN Adaptor

    DBS STB/MMDS/LMDSSTB

    Coax

    MMDS/LMDS

    56Kbps

    6Mbp

    s 640Kbps

    FiberONU Coax or

    CopperFiber

    52Mbps

    3Mbps

    30Mbps

    3Mbps

    64Kbps

    LMDS only

    HomeTerminal

    MSO

    /CO

    Hub

    StationFiber or

    Wireless

    Twisted-pair

    WMAX

    WiBro

    TP-based AN

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    BGL 4

    Access and Backbone Infrastructure

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    BGL 5

    Subscriber Line

    Central

    Office

    (CO)

    5.5 km

    Twisted-pair

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    BGL 6

    Limitation in existing subscriber lines Restrictive for high-speed service

    Limited data-carrying capacity of 56kbps using V.90

    Analog mode and suppressing filters above 3,400Hz

    Limitation of POTS Customer connected over thin-wire pairs (26guage, 24guage)

    Local loops are bundled in binder groups (feeder part)

    Limitation of ISDN services

    Not possible to provision ISDN and POTS in same local loop

    Problems in providing Internet services

    POTS and ISDN carry data in circuit mode (voice switch)

    Limitation of POTS and ISDN

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    BGL 7

    Advanced modulation technology basedbandwidth expansion (128kbps ~ 52Mbps)

    xDSL easier to install than ISDN

    needs inside wiring work and copper line cleaning

    Variations depending on symmetry ofupward/downward data rates (ADSL vs HDSL)and the location of equipment (ADSL vs VDSL)

    Supports POTS using splitter (split flter). ButG.Lite can eliminate splitter.

    HDSL can replace T1/E1 without repeaters (DLC).

    xDSL

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    BGL 8

    Digital Loop Carrier (DLC)

    Central

    Office

    (CO)

    Remote

    Termina

    l (RT)

    Carrier Serving Area

    (CSA)

    Feeder Line

    Multiple T1 Lines

    Fiber

    Distribution/

    Drop Wire

    Fiber LoopCarrier (FLC)

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    BGL 9

    Configuration of xDSL

    Central

    Office

    (PSTN)

    Central

    Office

    (PSTN)

    EndUser

    (POTS)

    Headend

    (Video)

    End

    User

    (Video)

    Headend

    (Video)

    End

    User

    (Video)

    PSTN POTS

    Optical

    Network

    Unit

    POTS

    ADSL

    CO UnitADSL

    RT Unit

    HDSL

    RT Unit

    HDSL

    CO Unit

    VDSL

    RT Unit

    VDSL

    CO Unit

    Line

    Repeater

    Line

    Repeater

    CO

    Repeater

    End

    User

    (POTS)

    PSTN

    T1/E1

    HDSL

    ADSL

    VDSL

    TP (2 pairs)

    TP (1 pair)

    TP (2 pairs)

    0.3~1km 1~1.8 km 0.3~1km

    TP (1 pair)

    SPF

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    BGL 10

    xDSL Genealogy

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    BGL 11

    ISDN Digital Subscriber Line is a cross pointbetween ISDN and xDSL

    Made available with the introduction of ISDN

    Circuit mode based integration of voice and dataNeeds ISDN terminals/adapters in the user side

    2B + D basic rate access(BRA),144kbps+16kbps

    B: 64kbps for voice or data

    D: 16kbps for call control or packet data

    Subscribers direct connection to CO

    IDSL

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    BGL 12

    23B + Dprimary rate access(BRA),1.544Mbps

    for the connections of PBXs, host computers, andLANs

    Transmission

    rate of 80 ksps

    2B1Q modulated,

    duplexing by TCM (time compressed multiplexing)ping pong

    Travels over 5.4 km over 24 gauge (.5mm)

    IDSL (contd)

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    BGL 13

    IDSL based Access System

    PSTN/ISDN

    Data Network

    ISP

    Voice Carrier

    System

    Switch

    Router

    ISDNNetwork

    Termina

    tion

    (NT1)

    Local Exchange Office Subscriber Premise

    Twisted-pair

    Subscriber Line

    ISDNNetwork

    Termina

    tion

    (NT1)AdapterAdapter

    Adapter

    PSTN/ISDN

    Data Network

    ISP

    Voice Carrier

    System

    Switch

    Router

    ISDNNetwork

    Termina

    tion

    (NT1)

    Local Exchange Office Subscriber Premise

    Twisted-pair

    Subscriber Line

    ISDNNetwork

    Termina

    tion

    (NT1)AdapterAdapterAdapterAdapter

    AdapterAdapter

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    BGL 14

    Comparable with T1/E1 lines Carrier level subscriber lines

    Beneficial to business users

    PRA at 1.544Mbps (T1) or 2.048Mbps (E1) rate

    Can replace T1/E1 lines without repeaters Can be used as feeder lines (for DLC systems)

    Transmission with 2 twisted pairs For T1 rate (1.5Mbps), two TP wires necessary

    For E1 rate (2Mbps), three TP wires necessary

    2B1Q Modulated, CAP, DMT

    2B1Q: 3.6km, CAP:5.5km over 24 gauge (.5mm)

    Interference problem when bundled in large size

    HDSL

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    BGL 15

    HDSL -- a simple means for loop transmission Transmits signals at normal power levels

    Equalizer can compensate for the TP signal distortion,

    Helps to restore the signal in the receiver regardless of

    changes in environmental conditions.

    Can maintain signal integrity even if TP wires are not perfect.

    Does not require cable conditioning or bridged tap removal.

    Becomes immune to crosstalk and polarity reversal.

    Overall system reliability and transmission performance

    improve.

    HDSL (contd)

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    BGL 16

    Symmetric (or Single-line)HDSL(SHDSL,SDSL)

    Single TP wire implementation of 2B1Q or CAP

    Enabled by advanced electronics for echocancellation and adaptive equalization

    Data rate of 192kbps~2.3Mbps (Sub-T1/E1 ratesobtainable)

    HDSL2 (G.SHDSL) standards

    Symmetric 2.3 Mbps over a single loop pair

    Symmetric 4.6 Mbps over two loop pair

    SDSL

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    BGL 17

    Up/down asymmetric bandwidth 1.5/2 ~6/8 Mbps down

    16~820 kbps up

    For use in Internet, VoD like applications

    One TP - good for residential use Up to 5.4km without repeaters (0.5mm)

    Uses advanced modulation techniques DMT (standardized)

    CAP (market)

    Enhancements Rate-Adaptive DSL (RADSL) - line condition

    Universal ADSL (UADSL) - without split filter

    ADSL

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    BGL 18

    TP diameter important to distance 1.5 or 2-Mbps channel

    Reaches 5.4-km over 0.5-mm, 4.6-km over 0.4-mm TP

    6-Mbps channel

    Reaches 3.6-km over 0.5-mm, 2.7-km over 0.4-mm TP

    POTS split through split filter (SF), or splitter

    Analog telephone service and the high-speed data service are

    FDM multiplexed

    300-3,300Hz band for voice, 26-1,100kHz band for data

    Splitter separates the two bands

    Protocol stacks for ADSL (see the figure)

    ADSL (contd)

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    BGL 19

    ADSL based Access System

    Receiving filterHybridcouplerHybridcoupler

    Demod/equalization/detection

    Ethernet

    Modulator

    Coder/decoder

    Pulseshaper

    Voice filter

    Subscriber line

    26 138 KHz

    .138 1.1 MHz

    Splitter

    0.3 3.3 KHz

    Transmitting filter

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    BGL 20

    Example Protocol Stack for ADSL

    TCP/UDP

    Computer(or appliance)ADSL terminal

    DSLAMDatanetworkterminal

    IP

    PPPEthernet

    Ethernet

    ADSL

    ATM(optional)

    ADSL

    ATM(optional)

    SONET

    ATM(optional)

    IP IP

    ISP

    SONET

    ATM(optional)

    IP

    PPP

    TCP/UDP Protocol servicessuch as DHCP

    Central Office Subscriber Premise

    Twisted pair

    subscriber line

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    BGL 21

    ITU G.992.2 standard

    Splitter set up is a hurdle in wide-spreading ADSL.

    Requires technicians labor for installation

    G.Lite is designed not to require splitter set up.

    Designed not to use splitter Uses customer-installable ADSL modems.

    G.Lite modem senses voice activity and controls power

    G.Lite modem cuts ba

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