ZL30461MGG ZARLINK [Zarlink Semiconductor Inc], ZL30461MGG Datasheet - Page 34

• Manufacturer Part Number: ZL30461MGG
• Description: COMPACT STRATUM 3 TIMING MODULE
• Manufacturer: ZARLINK [Zarlink Semiconductor Inc]

Two types of transitions are possible:
•
•
In both cases, the change of references provides “hitless” switching.
3.2
Carrier-Class Telecommunications Equipment deployed in today’s networks guarantee better than 99.999%
operational availability (equivalent to less than 7 minutes of downtime per year). This high level of uninterrupted
service is achieved by fully redundant architectures with hot swappable cards. Timing for these types of systems
can be generated by the ZL30461, which supports Master/Slave Timing Protection Switching, shown in Figure 11.
The redundant architecture shown in this figure is based on the ZL30461 being deployed on two separate timing
cards; the Master Timing Card and the Slave Timing Card. In normal operation, the Master Timing Card receives
synchronization from the network and provides timing for the whole system. All Line Cards in the system are
configured to receive from the backplane a reference clock generated by the Master Timing Card. The redundant
Slave Timing Card is phase locked (through the SEC input) to one of the backplane clocks supplied by the Master
Timing Card. The ZL30461 on the Slave Timing Card is programmed for 12 Hz loop filter operation (FCS2=1,
FCS=0) which allows it to track the Master Timing Card clocks with minimal phase error.
When the Master Timing card fails unexpectedly, (this failure is not related to reference failure), then all Line Cards
will detect this failure and they will switch to the timing supplied by the Slave Timing Card. At this moment the
ZL30461 on the Slave Timing Card must be switched from 12 Hz to the same loop filter characteristic (e.g. 1.5 Hz
filter for SDH networks) as the Master Timing Card.
Semi-automatic transition, which involves changing RefSel input to select a secondary reference clock
without changing the mode select inputs MS2, MS1 = 00 (Normal Mode). This forces ZL30461 to
momentarily transition through the Holdover state and automatically return to Normal state after
synchronizing to a secondary reference clock.
Manual transition, which involves switching into Holdover Mode (MS2, MS1 = 01), changing references with
RefSel, and manual return to the Normal Mode (MS2, MS1 = 00).
Master/Slave Timing Protection Switching
Reset
_____
Reset == 1
unconditional return from
MS2, MS1 == 10 forces
any state to FreeRun
FreeRun
10
MS2, MS1 != 10
Figure 10 - Manual Reference Switching
MS2, MS1 == 01 or
RefSel change
Zarlink Semiconductor Inc.
Holdover
ZL30461
01
MS2, MS1 == 00
Ref: OK &
34
{Auto}
RefSel change
(Locked)
Normal
00
Ref: OK --> Fail &
MS2, MS1 == 00
{Auto}
Holdover
Auto
Ref: Fail --> OK &
MS2, MS1 == 00
& AHRD=1 &
MHR 0 --> 1
{Manual}
Ref: Fail --> OK &
MS2, MS1 == 00
& AHRD=0 &
{Auto}
Data Sheet