Chapter 6. Center Office Noise and the End Section of a Repeatered Line

As stated earlier, in the end section next to the central office, maximum loss is limited to 50 to 70% of the normal loss limit (32 dB), or about 23 dB. The 23 dB limit includes the loss in the tip cable and in the office wiring to the line terminating shelf for office repeaters. If exchange service is mixed in the same cable with T1, then an extra safety factor of 8 dB should be allowed to tolerate impulse noise. This brings down the end section to a maximum of 15 dB. An end section of 15 dB represents approximately 3700 feet of cable, depending on the exact type. If this cable distance is too short to be economically tolerable, then consider leaving out the exchange service pairs to gain back the 8 dB safety margin.