 paging, 45/15 microwave, 50/16 RGB television signals, 57/5, 57/7 S service priority status, 25/6 optical, 53/18-22 Ring again, Centrex, 35/5 S/N see Signal to noise ratio paging, 45/4, 45/11-14 Ring architecture, multiple access, 13/13 Sabine (of sound absorption), 8/10 Index/19 SABM (Set Asynchronous Balanced thin route telecommunications, 51/17 Sensors, satellite positioning, 51/8 Mode), 54/9 transmissions for troposphere studies, Sequential scanning, 57/4 SAC (Standards Advisory Committee), Sequential tone signalling, 46/9-10 22/25 trunk telecommunications, 51/15-17 Service bureau, call management, 36/6 SACCH (Slow Associated Control Sawtooth waveform, 10/8 Service distribution, 3/4 Channel), PCN, 48/8 SBC (Sub Band Coding), 57/26 Service grade, network management, 16/5 Safety, SC6 of TC97 (ISDN/ISO relations), 22/13 Service providers, 11/5 earthing, 23/7-8 SC21 of TC97 (ISO seven layer model), Service values and classification, electric shock, 23/5 22/13 telecommunications, 11/16-18 insulation, 23/7 SCADA (Supervisory Control And Data SES (Severely Errored Seconds), 30/8 mains filters, 23/23 Acquisition), 52/11 Session layer, OSI, 12/9, 16/9 published reqirements, 23/8-9 SCAI (Switch to Computer Applications Seven layer OSI model see OSI service priorities, 26/6 Interface), Centrex, 35/5 SGMP (Simple Gateway Monitoring telecom basics, 23/3-4 Scanners, facsimile, 60/5-6 Protocol), TCP, 16/20 TNV circuits, 23/5-8 Scatter diagrams, 1/5 Shallow-water cable, 15/8 Sample-and-hold circuits, PCM, 19/13 Scattering, by ionosphere, 9/6 Shannon, Sampled signals, Laplace transforms, 2/13 Scattering loss, optical fibres, 15/11, applied to digital video, 57/12 Sampling, 1/9-10, 2/7-8 53/5-9 communications and information, 4/5 digital transmission, 19/3 SCC (Standards Council of Canada), modems max speed, 39/4 Nyquist theorem, 18/13-14 22/26 Shannon-Hartley theorem, 4/9 PCM, 19/12-13 SCH (Synchronisation Channel), PCN, Shannon's source coding theorem, 4/8-9 SAMs (Separate Absorption and Shared telephone service, 31/6 Multi