ABSTRACT
If a CP is used then the cable from the CP to the TO may be referred to as the CP cable. Centralised optical architecture (COA) may combine any of the above three cabling subsystems.
4.2.1 Categories and characteristic impedance One of the most important ways of describing the electrical perfor mance of a copper cable is by its characteristic impedance. Unlike impedance or resistance, the characteristic impedance is not length related, although it uses the same units of measurement, namely the ohm (Q) and has the symbol z0. In any electrical system it is essen tial that the output characteristic impedance of the transmission equipment is the same as the characteristic impedance of the cable system, which also has to be the same as the input characteristic impedance of the receiving equipment. If any of the elements in the transmission system have a different characteristic impedance then there will be electrical energy reflected back towards the source. In a power cable transmission system this could have disastrous effects upon the transmitter. In a communication system it is equivalent to an out-of-phase signal reflected back to the transmitter which will interfere and corrupt the data signal. In the field of structured cabling the amount of energy reflected back is called return loss, and it
can be one of the most troublesome factors to overcome in an installation, especially for the higher frequency Category 6 cable systems.
