System information

FCD 901 48
Issue R2A, 07.2009
XMP1 Release 5.5 System Description
SCU redundancy
Aastra Proprietary Information Page 3-13
The SSM value of outgoing STM-N signals can be set to 1111 (“Don´t use
for sync”) manually. Otherwise these signals will be assigned the SSM value
of the current clock quality of the internal T0 clock.
In case of plesiochronous signals, a SSM value is not transmitted. However,
for incoming plesiochronous signals configured as T2 reference timing
source , the operator can enter a SSM value and thus define the quality
manually. The same applies to the T3 clock which can be applied to the
external clock input.
In addition, each reference timing source can be assigned any priority
between 0 and 7: “0” means high priority, whereas “7” means low priority.
For all types of reference timing sources, the priority is assigned manually
by the user. This applies also to STM-N signals. The priority regarding the
use of T0 (internal system clock) and T4 (clock output) can be adjusted
separately.
The SETS selects the reference clock to be used according to the highest
clock quality (SSM). In case of identical quality, the higher priority
determines as to which reference clock will be selected.
3.6.3 SCU redundancy
The SETG functionality is doubled with the use of a second SCU module.
The active SCU then provides the SETG Master function and supplies the
internal system clock (for the SDH section) and T4 clock signal. The T4
clock signal can be selected using certain quality criteria.
The T1 timing sources of the active SCU (Master) are applied to the second
SCU (Slave).
The external timing interfaces T3 and T4 of the SCUs are connected via
Y-cables.
The following diagram shows the clock structure of the SCU.