363-206-285
Circuit Pack Descriptions
Issue 3 June 2001
7-95
Timing Circuitry 7
The BBG20 TMUX recovers DS3 clock from the DSX-3 incoming signal. In the
transmit direction, a 44.736 MHz clock is recovered from the incoming DS3 signal
and is used to recover DS3 data and to generate the clocks needed by the M13
device to convert the DS3 into 28 DS1s. The circuit pack provides a 44.736 MHz
clock to time the DS3 output signal.
In addition to the recovered DS3 clock, the BBG20 TMUX circuit pack requires
STS-1 timing supplied, via the circuit pack edge connector, from the backplane.
Protection Circuitry 7
Optional 1x1 nonrevertive BBG20 TMUX circuit pack protection is provided.
Switch points for the STS-1 side of the pack are located on the OLIU circuit packs.
Switch points for the DS3 side are implemented with relays on the BBG20 TMUX
circuit pack. To ensure that the relays can be operated when the circuit pack fails,
the relay is controlled by the SYSCTL via the control interfaces. Also, if power to
the board is lost, the relay switches autonomously to the standby state. When a
new board is inserted, it defaults to the standby state until provisioned active by
the SYSCTL.
On the DS3 side, a single DS3 input from a DSX-3 is sent to both the active and
standby BBG20 TMUX circuit packs. Only the active unit selects the DS3 input.
The SYSCTL supervises the state of the active and standby units so that the relay
state of each is always the inverse of the other. The hybrid on the active unit splits
the DS3 input signal and sends it to the standby unit and to its own receiver. To
implement a protection switch on the DS3 side, the SYSCTL switches the relays
on each unit to their opposite state.
When a BBG20 TMUX is removed, shorting contacts on the backplane connector
operate so that the DS3 input signal from its companion unit is returned for proper
termination.
Fault Detection Circuitry 7
The BBG20 TMUX circuit pack has in-service and out-of-service built-in test
capability. In-service testing is continuous and errors are reported when they
occur to the SYSCTL via the intra-shelf control bus. An out-of-service test is
performed whenever the BBG20 TMUX circuit pack is inserted or recovers from a
transient failure.
The incoming DS3 signal is monitored for parity threshold crossings in excess of
10
-3
or 10
-6
, LOS, DS3 OOF, and DS3 AIS. Incoming STS/VT signals are
monitored for STS/VT AIS, STS/VT LOP, STS/VT Unequipped, and yellow.
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