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In many situations customers' data sources will be low duty factor (e.g. randomly generated control signals, teletype keyboard outputs). Quality of service may be judged by the individual user in terms of overall transmission time as well as by error rate. Three systems are considered: The first is a base-line representing modest terminal equipment. Here each customer pair is multiplexed on a permanent cable time or frequency slot. Secondly, a more sophisticated system is analyzed, adaptive-rate code division multiplex. Here modulator waveforms are synthesized from sequences of phase-modulated and frequency-shifted carrier bursts. The number of bits sent per waveform is variable, dependent upon channel noise and interference observed just prior to message transmission. Lastly, a technique is considered which allows flexible sharing of total power and bandwidth, via status signaling between different customers.