Avaya 03-300430 User Manual

The Switch Node Clock (SNC) TN572 circuit pack is part of the Center Stage Switch (CSS) 
configuration. It resides in a switch node carrier that alone or with other switch nodes make up a 
CSS. In a high-reliability system (duplicated server and control network, unduplicated PNC), 
each SNC is duplicated such that there are two SNCs in each switch node carrier. In a 
critical-reliability system (duplicated server, control network, and PNC), each switch node is fully 
duplicated, and there is one SNC in each switch node carrier. SNCs are placed in slots 10 and 
12 of the switch node carrier.
The active SNC communicates with each circuit pack in the switch node carrier over the serial 
channel bus on the backplane. In addition, the active SNC provides timing to the circuit packs in 
the switch node carrier via the clock buses. The active SNC uses Timing Priority Number (TPN) 
links with each Switch Node Interface (SNI) and the other SNC to receive and distribute TPNs. 
TPNs are used for setting up the correct timing distribution for the switch node carrier. The 
active SNC receives timing for the switch node carrier from each SNI circuit pack in the carrier 
and chooses the SNI with the best timing reference for the switch node carrier timing signal the 
SNC puts out on the clock buses. The timing reference for each SNI is derived from the fiber 
signal to each SNI. The active SNC chooses the SNI to receive timing from by choosing the SNI 
with the lowest numbered TPN which means that the SNI is closest to the system timing source. 
The active SNC also verifies that the SNI reference signal is good before using that SNI as the 
timing reference for the switch node carrier. The active SNC then supplies this timing over the 
clock buses on the backplane to every SNI and SNC circuit pack in the carrier. For more 
information about timing synchronization (including how the SNC fits into the overall 
synchronization configuration), see 

The SNC circuit packs are associated with three MOs:

●

The 

on page 2000 MO covers general SNC 

board errors and errors with the serial communication channel between the active and 
standby SNCs.

●

The 

on page 2039 MO covers errors between the 

active SNC and SNIs over the serial channel (Aux Data is 1). Also, the SNC-LINK MO 
covers TPN Link errors between the active SNC and SNIs (Aux Data is 2).

●

The 

on page 2043 MO covers errors the active 

SNC detects with SNI reference signals.

SNC circuit packs are part of port-network connectivity (PNC). For background information 
about PNC, refer to the Maintenance Architecture and Hardware Configurations chapters.

SNC-BD

MAJ

test board location s

SNC Circuit Pack

SNC-BD

MIN

test board location s

SNC Circuit Pack