Specifications

Chapter 7 Battery Reversal FXS/DPO
7-2
OVERVIEW OF OPERATION
The reversible-battery FXS channel card is designed to provide twelve 2-wire analog interfaces to the
digital T1 (DS1) line. Currently, the analog loops (also called CPE loops in this document) must always
be loop-start.
One of the main features of the analog interface is that the polarity of the battery feed towards the
customer-premise equipment (CPE) can be reversed in response to the signaling bits coming from the T1
line.
• The basic operation is selected by setting Switch A off so that no ringing voltage is applied towards
the CPE. If desired, Switch B can be turned on to give a cadenced (2-second/4-second) ringback
tone to the T1 line during incoming calls. The battery to the CPE loop will be reversed to indicate
an incoming call. The battery will return to forward polarity again when the call has ended.
• Also included in this channel card is a setting to provide cadenced ringing voltage (if needed by
other customer-premise equipment). This option is enabled by setting Switch A on so that
cadenced ringing voltage will be applied to the CPE loop during an incoming call. The battery is
reversed during this time. If desired, Switch B can be turned on to give a cadenced (2-second/4-
second) ringback tone to the T1 line during incoming calls, that is synchronized to the ringing
voltage present on the loop.
Note: During a two-way call, the CPE -loop battery is reversed. To disconnect the call either the CPE loop
current ceases or the network sends A/B bits = 0/0. The reversed state of the CPE loop, however,
will be maintained until the network terminates (releases) the call.
BRFXS/DPO APPLICATIONS
As explained above, the two major applications for the BRFXS/DPO card are FXS with battery reversal
“wink” to signal a PBX timer to start billing a call and Dial Pulse Origination (DPO) termination for
transport of Direct Inward Dialing (DID) lines. Refer to Figure 8-1 and Figure 8-2 for pictorial
representations of these two applications.
PBX
BRFXS
T1
FXS Loop-Start Lines
Battery Reversal
to PBX
Optional Cadenced
Ringback
Tone to T1 during
Incoming Calls
Optional Cadenced Ringing
Voltage applied to CPE
During Incoming Call
Figure 8-1. Battery Reversal FXS Loop-Start for Starting PBX Billing Timer