This section of 60835-2 deals with measurements pertaining to the service channels used in digital microwave radio-relay systems. In digital radio-relay systems, two basic methods are commonly used for the transmission of service channel signals (that is voice, supervisory and control signals)(see annex A, ref. (6)). The first transmission method uses analogue transmission techniques where the i.f. or r.f. carrier signal of the digital modulator is directly frequenxy.modulated by the analogue service channel signal, which is then recovered atthe receive end by an f.m. demodulator (for example in the carrier recovery circuit of a coherent digital demodulator). In the second method of transmission, digital transmission is used and the service channel signal is transmitted in the form of separate bits inserted into the main bit stream by a multiplexer (possibly together with a bit stream carrying additional information).