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A Technical Analysis of the Common Carrier/User Interconnections Area (1970) / Chapter Skim
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Section 5-- Protective Devices
Pages 40-47

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From page 40...
... Private-line customers obtaining service under FCC tariff 260 are not, in all cases, required to obtain protective devices. This Section discusses this concept of protection along with alternative arrangements.
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From page 41...
... Some of the more complex forms of coupler include a more sophisticated signal limiter designed to reduce distortion of data signals that exceed the allowable limits. Others include arrangements for signaling and supervision, either manual or automatic, answering only, or answering and calling.
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From page 42...
... Since all elements are solid-state, life under normal operating conditions is indefinitely long. Transformerinsulation failure at telephone-line voltage is extremely rare unless the quality of the insulation is initially poor.
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From page 43...
... Redundancy Redundancy, for purposes of this discussion, means that essential functions are duplicated in the coupler and in the devices attached to it and the requirement for protection, in many cases, can cause such a redundant condition. For example, redundancy occurs in some of the couplers provided for use with PBX's; In these cases ,all functions of the coupler are repeated within the PBX itself from transformer isolation to regeneration of subset dial pulses which themselves may meet the dial criteria.
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From page 44...
... A lack of uniform interpretation among the many telephone companies and the various state Public Service Commissions is also a factor. Power Supply Dependence P.otective arrangements (above the simplest level)
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From page 45...
... Presently, the protective device cannot be physically located in the customer's equipment, although the carrier indicates it is willing to discuss this issue. Integrated Protection Assuming a Certification program3to allow direct connection between carrier and users, the following are some factors involved in the inclusion of the protective arrangement within the equipment cabinet.
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From page 46...
... Protection in the central office could, in principle, prevent excessive levels on carrier systems in the trunk plant. Present central-office designs, however, do not provide facilities to limit signals to the levels required to prevent overloading carrier systems or to prevent cross talk in loops or on voice-frequency intertrunks.
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From page 47...
... Existing carrier-provided protective devices are indeed effective in providing protection for hazardous voltages, excessive signal amplitudes, and longitudinal unbalance from users.
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Key Terms

  • protective devices
  • protective arrangement
  • central office
  • hazardous voltages
  • telephone network

  • network control
  • dial pulses
  • isolation transformer
  • providing protection
  • cross talk

  • ideal protective
  • telephone central
  • longitudinal unbalance
  • pbx equipment
  • power supply

  • longitudinal balance
  • normal operating
  • signal amplitudes
  • excessive signal
  • coupling arrangements

  • transformer isolation
  • limit signal
  • operating conditions
  • control signaling
  • obtain protective

  • protective coupler
  • dial pulse
  • prevent cross
  • terminal equipment
  • coupling unit


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