This part of IEC 61334 describes the requirements of S-SFK (frequency shift keying modulation) in conjunction with the services provided by the physical layer entity and the MAC sublayer. The transmission medium is assumed to be the distribution network on both MV or LV level. The MAC sublayer described in this standard interfaces with the logical link control layer described in IEC 61334-4-32. The three parts – modulation, physical layer and MAC sublayer – are matched to each other so that an optimum cost-performance relation can be achieved. The profile described in this standard is one of several profiles (described in series IEC 61334-5) which are all designed for data transmission via the distribution network. Considering the ongoing technical development in this field, the profiles are published first as technical specifications with the intention to transform into standards those profiles which are successful in practice.