ul. Reservation Aloha (R-ALOHA). Short stack. Implementation of only some of the lower layers of Return loss. Difference, measured in decibels, between the inci- the full OSI seven layer model (stack) within an equipment. dent energy and the reflected energy, at a signal reflecting point. Sideband. Signals generated above and below the central carrier Residual error rate. The error rate remaining after going through frequency, during modulation, the extent of the sideband being error correction systems. determined by the modulating signal used. Response time. In a real time system it is the delay between the Sidelobes. Refers to the response of an antenna off its axis. end of a message and the beginning of the response to that Sidetone. Transmission of sound from the microphone to receiver message. of the same telephone. Two customers may therefore see quite Ringback. The signal which is fed back to a caller to indicate that different sidetone conditions at their respective ends. the called telephone is ringing. Signal ground. A common reference potential for all signal Ringing signal. Signal sent over the line to the called party, to ring carrying circuits within the equipment. his telephone, to indicate that he is being called. Signalling. The transmission of information relating to switching, Ring network. A network topology in which each node is con- such as address, between switching systems or between sub- nected to two other adjacent nodes, so as to form a ring. scriber and switching system. Rise time. The time needed for a signal pulse to rise from 10% to Signal skew. Offset between two signals. 90% of its maximum value. See also fall time. Signal to noise ratio. Measure of the strength of a transmitted Roaming. Ability of a mobile communications device to switch signal relative to the background noise, measured in decibels. from one transmitter to another. Simplex. System in which transmission can occur in one direction Robbed bit signalling. Signalling system, used in North America, at a time only. in w