R2 Signalling - Signalling Variants

Signalling Variants

R2 line signalling variants that support R2 line signalling in its electrical-pulse form by dedicated two-wire or four-wire circuits usually represent each signal as two different pulse lengths (e.g., 150 milliseconds versus 600 milliseconds), where the two different meanings of those two different pulse lengths varies by context.

R2 line signalling variants that support R2 line signalling in its digital form via the A, B, C, and D bits in DS0 channel #16 of an E1 fall into two general categories: those that use only the A bit to represent each signal and those that use multiple A, B, C, and D bits to represent each signal, with using only two, the A bit and the B bit being by far the most common. Those that use only the A bit, strongly resemble the analog electrical R2 line signalling, where each signal is a timed pulse that differs by length of time that the pulse is in the high voltage (i.e., one-valued bit) state before returning to the untimed resting voltage state (i.e., zero-valued bit). Those that use multiple bits to represent each signal usually are stateful in that time of exhibition of that bit pattern typically plays no role in conveying meaning.