Type V is a
modified version of the Type I interface. In the Type V interface, the Cisco
voice equipment (tie-line equipment) supplies battery for the M-lead while the
PBX supplies battery for the E-lead. As in Type I, Type V requires that a common
ground be connected between the PBX and the Cisco voice equipment.
Types II, III, and IV are eight-wire interfaces, where the
eight wires include the voice path. One wire is the E-lead; the other wire is
the M-lead. Two other wires are SG and SB. In Type II, SG and SB are the return
paths for the E-lead and M-lead, respectively.
The Type II interface, depicted in Figure 2-14, exists for applications where a common ground
between the PBX and the Cisco voice equipment (tie-line equipment) is not
possible or practical. For example, the PBX is in one building on a campus and
the Cisco equipment is in another. Because there is no common ground, each of
the signals has its own return. For the E signal, the tie-line equipment permits
the current to flow from the PBX; the current returns to the PBX SG lead or
reference. Similarly, the PBX closes a path for the current to generate the M
signal to the Cisco voice equipment (tie-line equipment) on the SB lead.
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