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T1/T3 Applications and Subscriber Loop Carrier Systems


... /T3 Applications Channel banks Multiplexers 2- Subscriber Loop Carrier Systems SLC 96 SLC 5 3- Fiber to the home 4- Wave Division Multiplexing Lecture 6: ... – PowerPoint PPT presentation

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Title: T1/T3 Applications and Subscriber Loop Carrier Systems

Chapter 3
  • T1/T3 Applications and Subscriber Loop Carrier

Chapters Outline
  • 1- T1/T3 Applications
  • Channel banks
  • Multiplexers
  • 2- Subscriber Loop Carrier Systems
  • SLC 96
  • SLC 5
  • 3- Fiber to the home
  • 4- Wave Division Multiplexing

Lecture 6 Summary
  • T1 Applications and Equipment
  • T3 Applications and Equipment
  • Operations of Digital Loop Carrier (DLC)
  • SLC 96 (Bellcore TR08) system
  • ATT SLC Series 5 Carrier system
  • Testing customer loops in a digital environment
  • Litespan 2000 system,
  • Fiber to the home
  • Wave division multiplexing - brief outline

  • In this lecture, we will change gear from bits
    and bytes to seeing the application of digital
    transmission in the public telephone system
  • T1/T3 found their ways into customer applications
    in addition to being integral parts of the
    backbone networks
  • Selecting T1/T3 equipment require a good
    understanding of the technical features as well
    as the economic implications

T1 Equipment and Applications
  • Selecting T1 equipment can be complex - some of
    the factors are
  • equipment growth limitations
  • financial considerations
  • ongoing maintenance and operation
  • The dynamic of the market new companies entering
    and others going out of business, less stable
    companies are barely hanging on

T1/T3 equipment selection criteria
  • friends Price Initial cost is only a fraction of
    the overall system price
  • Functions Functions of today may not be suitable
    for future growth of the organization upgrading
    from voice only service to voice and data for
  • Emotion It could become a problem if the user
    become enamored with the bills and whistles of
    a hardware vendor, or if the seller and buyer
    become very close

T1/T3 Selection Criteria
  • End of life cycle often when a new product is
    about to be introduced, old product are heavily
    pushed. How long the old product will be
  • Technological Changes As new features are
    developed such as ISDN, broadband ISDN, ATM,
    frame relay, and introduced, the hardware must be
    able to grow with the technology. If not
    limitations may exist for future uses of the
    system and the network.

T1/T3 Selection Criteria
  • Standards Standards are constantly changing,
    newer systems must be able to work with older
    ones, and current systems must still work with
    future ones

Examples of T1 equipment
  • Channel banks
  • Multiplexers
  • Network processors
  • Digital Access Crossconnect Systems (DACS)
  • Electronic Switching Systems
  • LAN connectivity bridges
  • WAN connectivity router and gateways

Channel banks
  • The first devices used by customers to interface
    to a T1 circuit
  • Was initially designed customers using voice-only
  • Combined 24 voice signals onto a single DS1 bit
    stream, transmitted either over a customers
    private network or a carrier (public) network
  • Data transmission was handled using modems

Channel Banks
  • The evolution to a D4 (superframe) allowed voice
    and data. A DSU (Data Service Unit) can be
    plugged in the D4 channel bank cage to carry data
    at up to 56 kbps digitally
  • D4 channel banks are the least expensive, from
    2500 to 5000

T1 Multiplexers
  • They are the next step above channel banks
  • They provide more flexibility
  • channelized services (24 fixed time slot for each
    DS1 stream)
  • non-channelized services
  • Support multiple interfaces using a wide range of
    plug-in cards for
  • superrates gt 64 kbps
  • subrates lt 64 kbps

T1 multiplexers
  • General features
  • Terminal Interface, unlike D4 channel bank where
    configuration takes place by setting jumpers - T1
    MUXs use a dumb terminal and an RS232
    interface. The terminal is also used to run
    diagnostic tests and on the fly changes.
  • Voice, Data, and Video Handling, It can handle
    signals from different types of sources. It I
    sable to integrate serial bit streams into an
    integrated bit stream (DS1). A video call may
    require 384, a voice call may require 32 kbps.

T1 Multiplexers
  • Support for Different Standards, It is possible
    to select companding laws U-law, and A-law, type
    of modulation standard PCM, delta modulation, or
  • Vendor Specific Voice Compression, It may allow
    high-compression rates voice multiplexing at 16
    and 8 kbps. One 64 kbps timeslot can be used by 8
    telephone users

T1 Multiplexers
  • General Architecture
  • Power panel
  • Frame
  • Common control logic, to provide control
    functions such as configuration, modes of
    operation, diagnostics. That is why the MUX needs
    only a dumb terminal
  • Card cage, to house service cards

T1 Multiplexers
  • Interface cards (voice, data, aggregate cards)
  • Backplane, an internal digital bus over which
    digital traffic flows internally until possible
    conversion and formatting is done for
    transmission over the T1 line or lines
  • Equipment interfaces circuits and devices such
    as T1 interfaces, voice to connect to telephone,
    data interfaces to connect to computers and
    possibly interfaces such as V.35 and RS336 to
    enable video calls.
  • Management and diagnostics software
  • Special interface cards (LAN, bridges, and

Channel Service Unit - CSU
  • Although not a major expense, it provides the
    interface between the the customer equipment and
    the network - Older implementations had it as a
    separate piece of equipment. Newer design
    integrates into the MUX, PBX or other T1
  • Its functions are required by the FCC, and they

Channel Service Unit - CSU
  • Electrical isolation from the line
  • Signal generation compatible with the line
  • Assures 1s density, B8ZS or ZCS, if necessary
  • Bipolar violation correction
  • Responds to carrier (interface exchange carrier)
    loopback requests
  • It has an interface for local loopback
  • Collection of ESF data, if equipped
  • Test pattern generation for error checking
  • Framed 1s pattern sent if equipment failure

The Digital Service Unit - DSU
  • Its primary function is to
  • convert a unipolar signal from customer data
    terminal equipment (DTE) into a bipolar signal
    for the network
  • and from bipolar to unipolar in the opposite
  • ensures 1s density, bipolar signaling, extract
  • New implementations integrates the CSU and DSU
    into T1 equipment

Digital Service Unit - DSU
T1 - Equipment, Private Business Exchange
T1 Equipment, private business exchange
  • Will be discussed later in more detail
  • It provides a direct termination of T1 line into
    a digital a trunk interface
  • T1 in a PBX environment is typically a shelf. The
    T1 line can interconnect two PBXs or connect a
    PBX to a central office switch.

T1 Equipment, PBX
  • The PBX offers some features that are not
    accessible the multiplexers such as
  • station message recording
  • queuing a channel on a T1
  • least cost routing
  • redialing a busy number
  • call transfer
  • conferencing
  • call forwarding
  • hunting
  • and others

Digital Access Crossconnect System- DACS
  • A switching system (mainly static), by using
    time-division multiplexing scheme, switches or
    crossconnects digital bit streams.
  • The number of inputs the number of outputs
  • Non-blocking connectivity - for each input there
    is a rout on the output side
  • Was initially designed to simplify the Telephone
    Companys administration and testing procedures,
    network grooming, and dynamic reconfiguration of

  • Although was originally designed for use in the
    carrier network, larger corporations have
    implemented DACS configurations.
  • it allows drop and insert capabilities, drop some
    channels off and insert new bit streams into
  • They can support very large amount of bandwidth,
    up to 960 T3 ports.

Digital Access Crossconnect System - DACS
Digital Access Crossconnect System - DACS
DACS in T3 Environment
  • New generation DACS may include
  • Digital services for customer or carrier
  • network administration
  • port-by-port, channel-by-channel reconfiguration
  • changes to user networks on demand
  • network recovery and switching
  • local balancing

Digital Access Crossconnect Systems - DACS
Digital Access Crossconnect System - DACS
T3 Multiplexers
Digital Loop Carrier (DLC) Systems
  • A transport system in the local loop
  • Let us look at the public network hierarchy and
    where the subscriber loop carrier (SLC) system
  • The most popular DLC is the SLC96, also known as
    TR08 system.
  • TR08, a Bellcore document issued in 1987
    describing the operations of SLC96
  • ATT was ordered to make SLC 96 public after the

Generic DLC system
Digital Loop Carrier (DLC) Systems
  • SLC96 technology is not at the cutting edge,
  • There is large base of SLC 96 installed
  • Also there is a large base of SLC96 channel units
    and SLC96 clone channel units in use.
  • Example of channel units
  • POTS
  • Ring down
  • special service - for data communications

SLC 96
  • Remember, the idea of the SLC96 is to reduce the
    number of cables between the central office and
    the customer locations, while maintaining an
    economic advantage
  • for example if it costs the telephone company
    500 to install each line using SLC96 and 180
    using regular copper, what would you do if you
    have to make the decision - SLC96 the plain old
    twisted pairs.

SLC 96
  • The name implies 96 voice grade line
  • With concentration, this can be increased to 192
    voice grade lines per a single SLC96 bank.
  • All TR08 systems include two boxes, the COT and
    the RT
  • The COT is located next to the switching
    equipment in the local exchange
  • The RT is usually located near the subscribers

SLC 96
SLC 96
  • Protection switching
  • 5 T1 lines (D4 format)
  • 4 for normal operation and 1 for protection
  • if any of the 4 T1 lines fails, its bit stream is
    switched onto the protection line
  • If more than one line fail, what do you think
    will happen

SLC 96
Review of the SLC 96 System
  • Two banks The COT and the RT
  • The COT resides near the Central Office equipment
  • The RT location is near the customers premises
  • The COT and the RT are interconnected via 5 T1
    lines 4 lines supporting 96 And 1 line for
    protection switching

Limitations of SLC 96
  • Uses D4 superframe framing format
  • Each POTS channel unit card support tow
    telephones and thus uses two time slots and one
    physical slot for two connections
  • If special services channel units are used, one
    physical slot and two time slots for one
  • No system level maintenance testing for special
    service channel units. Uses D1D assignment of
    time slots.

SLC Series 5
  • Enhanced Features over SLC 96
  • Various feature packages to support different
  • In normal modes of operations, it also uses a COT
    and RT.
  • Each of the COT consist of two banks, thus
    doubling the capacity of the SLC96
  • The banks are called literally the blue and the
    white banks.

SLC Series 5
  • Offer a variety of feature packages ( out of
    which one that makes a SLC Series 5 operate just
    like a SLC 96)
  • Offer a wide range of special services units FXO
    channel units to connect to foreign exchange
    switches, data services channel units, Support
    for ISDN services, Support for different types
    compression techniques (PCM and ADPCM) -

SLC Series 5
  • It can double its operation capacity by using
    concentration ( 32 kbps per each voice
    connection). How many bits in a PCM word in this
    mode will be used.
  • Feature packages to incorporate development
    tailored for particular customer needs Feature
    package A, B, C, I, G.
  • Offers advanced maintenance features such as
    craft interface (CIU), centralized operation
    procedures (COP) and support for PGTC and XTC

SLC Series 5
  • Provision and testing of special service channel
    unite at the remote terminal using the craft
    interface unit.
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