363-206-285
Circuit Pack Descriptions
7-70 Issue 3 June 2001
Control Circuitry 7
The BBG4/BBG4B DS3 circuit pack interfaces with the SYSCTL via the intra-shelf
control bus. Redundancy in the intra-shelf control bus assures the level of control
required to perform protection switching and alarming of a faulty circuit pack. The
BBG4/BBG4B DS3 provides maintenance elements for reporting the status of the
circuit pack, status of the incoming STS-1 and DS3 signals, as well as the circuit
pack inventory information (
CLEI
code, date of manufacture, etc.). These
maintenance elements are used by the SYSCTL for fault detection and isolation.
Conversely, the BBG4/BBG4B DS3 responds to control signals from the SYSCTL
(such as active and fault LED controls).
Timing Circuitry 7
The BBG4/BBG4B DS3 derives its timing information from the recovered 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.
In the receive direction, a smoothed 44.736 MHz clock is generated by a phase-
locked loop to accompany the DS3 signal extracted from the STS-1 payload.
In addition to the recovered DS3 clock, the BBG4/BBG4B DS3 circuit pack
requires STS-1 timing supplied, via the circuit pack edge connector, from the
backplane.
Protection Circuitry 7
Optional 1x1 nonrevertive BBG4/BBG4B DS3 circuit pack protection is provided.
Switch points for the STS-1 side of the DS3 are located on the OLIU circuit packs.
Switch points for the DS3 side are implemented with relays on the BBG4/BBG4B
DS3 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 BBG4/BBG4B DS3 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 BBG4/BBG4B DS3 is removed, shorting contacts on the backplane
connector operate so that the DS3 input signal from its companion unit is returned
for proper termination.
To Next Page
Loading...
Need help?
General
