7.3
SIGNALING TECHNIQUES
153
exchange, its application is E&M signaling. In other words, out-of-band signaling is one
method of extending E&M signaling over a carrier system.
In the short run, out-of-band signaling is attractive in terms of both economy and
design. One drawback is that when channel patching is required, signaling leads have
to be patched as well. In the long run, the signaling equipment required may indeed
make out-of-band signaling even more costly because of the extra supervisory signal-
ing equipment and signaling lead extensions required at each end, and at each time that
the carrier (FDM) equipment demodulates to voice. The major advantage of out-of-band
signaling is that continuous supervision is provided, whether tone on or tone off, dur-
ing the entire telephone conversation. In-band SF signaling and out-of-band signaling
are illustrated in Figure 7.2. An example of out-of-band signaling is the regional sig-
naling system R-2, prevalent in Europe and nations under European hegeonomy (see
Table 7.1).
Figure 7.2
SF signaling (a) in-band and (b) out-of-band.
Summary :
In the long run, the signaling equipment required may indeed make out-of-band signaling even more costly because of the extra supervisory signal- ing equipment and signaling lead extensions required at each end, and at each time that the carrier (FDM) equipment demodulates to voice.
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