T1T3 Applications and Subscriber Loop Carrier Systems

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Chapter 3

• T1/T3 Applications and Subscriber Loop Carrier
  Systems

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Chapters Outline

• 1- T1/T3 Applications
• Channel banks
• Multiplexers

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• T1 Applications and Equipment
• T3 Applications and Equipment

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Introduction

• 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

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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

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T1/T3 equipment selection criteria

• 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
  example
• 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

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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
  supported
• 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.

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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

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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

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Channel banks

• The first devices used by customers to interface
  to a T1 circuit
• Was initially designed customers using voice-only
  services
• 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

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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

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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

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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 is
  able to integrate serial bit streams into an
  integrated bit stream (DS1). A video call may
  require 384, a voice call may require 32 kbps.

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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
  ADPCM
• 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

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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
  equipment
• Its functions are required by the FCC, and they
  are

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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
  occurs

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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
  direction
• ensures 1s density, bipolar signaling, extract
  timing
• New implementations integrates the CSU and DSU
  into T1 equipment

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Digital Service Unit - DSU
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T1 - Equipment, Private Business Exchange
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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.

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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

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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
  ports

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DACS

• 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
  channels.
• They can support very large amount of bandwidth,
  up to 960 T3 ports.

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Digital Access Crossconnect System - DACS
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Digital Access Crossconnect System - DACS
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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

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Digital Access Crossconnect Systems - DACS
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Digital Access Crossconnect System - DACS