Verilink PRISM 3030 (34-00208.L) Product Manual - Manual (Page 96)

86 A PPENDIX B: FXS V OICE A PPLICATION M ODULE
Loop Start
Signalling (FXS)
Idle The application module has ground applied to the tip conductor and has
−
48 VDC
applied to the ring conductor towards the 2 -wire loop. The 2 -wire loop is open
(no DC path between the tip and ring conductors). The transmit A bit is set to 0
and the B bit is set to 1. The receive A bit (from the FXO application module) is
set to 0 and the B bit is set to 1.
Ringing During ringing, the office end (FXO) changes the state of the B bit from a 1 to a 0
and holds the A bit to a 0. The FXS application module detects the change in state
of the B bit and reacts by applying the ring generator to the 2-wire loop.
The ringing cadence (typically two seconds on and four seconds off) is provided
from the office end and is controlled by the 0 or 1 state of the B bit. The phone
rings until the call is abandoned by the calling party (FXO end) or the called party
goes off-hook.
Off-Hook/
Ring Trip
During ringing, the FXS application module is looking for an off-hook (loop
closure) condition. When the FXS detects the off-hook, the FXS application
module sets the A bit from a 0 to a 1. The B bit remains set at 1.
FXO Answer
Supervision
The change in the state of the receive A bit status from a 0 to a 1 causes the FXO
to place a loop closure on the 2 -wire path toward the CO switch. This loop closure
trips the CO ringing and cuts through the voice path. The call is now complete.
Call
Request
The user goes off-hook at the FXS end. The FXS unit detects the off-hook and
signals the office end by changing the state of the A bit from a 0 to a 1. The B bit
remains set at 1. The FXO application module responds by placing a loop closure
on the 2 -wire towards the CO switch. The CO switch responds by returning dial
tone to the FXS end. The user detects a dial tone and dials out using either dial
pulse or DTMF. The dial pulse toggles the state of the A bit at a rate of 10 pulses
per second (60 percent make and 40 percent break).
Ground Start
Signalling (FXS)
Idle The FXS application module has the tip conductor open and
−
48 VDC applied to
the ring conductor toward the 2 -wire loop. The 2 -wire loop is open (no DC path
between the tip and ring conductors). The transmit A bit is set to 0 and the
transmit B bit is set to 1. The receive A bit equals 1 and the receive B bit is
ignored.
Outgoing Call
(toward T1
Carrier)
The ring conductor is grounded by the CPE equipment on the 2 -wire loop. This
causes the FXS application module to transmit both A and B signalling bits equal
to a 0. The network equipment responds and the FXS application module receives
a signalling bit equal to 0 and a B signalling bit equal to 1.