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Section 3-- Transmission and Protection Considerations
Pages 21-32

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From page 21...
... , THE :PANEl HAS CONCLUDED THAT THE SIGNAL CRITERIA rN THE TARrF:fS ARE REASON ABLE. SrGNALS WHICH VIO LATE THESE CRITERIA CAN CAUSE HARM BY INTERFERING WITH SERVICE TO OTHER USERS We discuss next the sources and effects of harmful voltages on personnel and plant, the exposures of the telephone system to these .
From page 22...
... and energy distribution introduced by this e~uipment must continue to conform to the parameters used in the overall netWork design. Even a single user, whose signals are such as to cause cross talk or interference in multi-pair cable systems or cause overload in broadband carrier systems, can cause serious deterioration of service to a group of users.
From page 23...
... Telephone cables are very carefully manufactured to minimize unwanted pickup of interference -- either from other telephone circuits or from nearby power systems. It is necessary to maintain this longitudinal balance at all times on all pairs, If this balance is degraded by some attached equipment, not only will interference be present on the unbalanced pair, but also other pairs in the same cable will be disturbed.
From page 24...
... . These restrictions safeguard the6periition of the 2,600 Hz in-band signa1~ng system, which is a1~ost universally used in long-distance telephone service, False operation of the in-band signaling system has serious results: improper billing, intermittentinter'i;uptions, insertion of a band-elimination filter in the transmission path, or evencrnnp1ete disconnection of a call, As a part of this study, the Panel has examined the structure of the te1ephone-crnnpany plant and has determined'that it does not provide protective mechanisms by either level 1imite;rs or filters to co;rrect for signals exceeding criteria limits, We have also examinedtheoperiition of the te1ephone-crnnpany plant and have determined that the system is designed to operate in accordance with the criteria.
From page 25...
... The selected location was the serving central office and the usual loss between this point and the equivalent network reference transmission level point is ldB. Thus, the maximum signal power that may be permitted at the central office is -12dBm when measured over any three-second interval.
From page 26...
... Comlllete loss of serVice caused by catastrophic overload of Une facilities, The netWork of 10ng"distancefaci1ities to which the in"band power criterion is applicable is used on a1~ost all long"distance connections (over 200' miles' in length) , 1'h±.s network provides ~any diverse paths over which voice and data calls ~ay be carried, NetWo:tk""lllanagement techniques plus dynamic alternate Touting plans vary the specific path (and specific broadband facility)
From page 27...
... Using this limit, the 4 to 10kHz criterion is calculated as follows: -47dBm Maximum. noise Correction for measuring techniques 5 and allowance for maintaining margin -10dBm Correction for multiple disturbers - 3dB System equalization -25dB Cross-talk coupling loss at 8kHz 6.9dB Allowable 4 to 10kHz power on disturbing pair -16dBm 5Broadcasters normally use nonweighted noise measurements and align their equipment at 400Hz, while the Telephone Company uses weighted noise measurements and aligns audio channels at 1,000 Hz.
From page 28...
... However, . 1ooking ahead to increased copper costs and reduced electronic costs, it is expected that loop systems operating in this frequency range will likely be used to an increased extent.
From page 29...
... Signal Criteria (Criteria for Distribution of In-Band Power) The tariff requirements concerning distribution of power within the transmission band are: FCC 259, FCC 260, FCC 263 -- to prevent the interruption or disconnection of a call, or interference ~nth network control signaling, it is necessary that the signal applied by the userprovided equipment to the Telephone Company interface located on the user's premises at no time have energy solely in the 2.450-to-2,750 Hz band.
From page 30...
... As explained, the telephone companies provide service to customers by means of physical conductors in the exchange plant. Each time service is installed, removed or repaired, telephone servicemen make physical contact with wire pairs and terminals at one or more points in the station equipment or at the terminal appearances of the wire pairs on customer premises in outside manholes or on poles, and in the central office building.
From page 31...
... Effects of Interconnection on· the· Harmful-Voltage· Problem The direct electrical connection of user-provided equipment and communications systems to telephone company lines adds an add it iorta1 source for the introduction of potentially harmful voltages into the telephone plant. This can come about by a faulty equipment design or manufacture, or a faulty installation, both of which could cause 110 V AC or higher to appear on the loop.
From page 32...
... to maintain balance and reduce cross talk, these controls become ineffective if equipment attached to the cable pairs is itself improperly designed, installed,or maintained. Cross talk will result if user-provided equipment is unbalanced to ground.


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