Nokia 7210 SAS-M User Manual

System Management
270
7210 SAS-M, T, R6, R12, Mxp, Sx, S Basic System
Configuration Guide
3HE 16132 AAAB TQZZA Edition: 01
The synchronization network is designed so a clock always receives timing from a
clock of equal or higher stratum or quality level. This ensures that if an upstream
clock has a fault condition (for example, loses its reference and enters a holdover or
free-run state) and begins to drift in frequency, the downstream clock will be able to
follow it. For greater reliability and robustness, most offices and nodes have at least
two synchronization references that can be selected in priority order (such as primary
and secondary).
Further levels of resiliency can be provided by designing a capability in the node
clock that will operate within prescribed network performance specifications without
any reference for a specified timeframe. A clock operating in this mode is said to hold
the last known state over (or holdover) until the reference lock is once again
achieved. Each level in the timing hierarchy is associated with minimum levels of
network performance.
Each synchronization capable port can be independently configured to transmit data
using the node reference timing. In addition, some TDM channels can use adaptive
timing or loop timing.
Transmission of a reference clock through a chain of Ethernet equipment requires
that all equipment supports Synchronous Ethernet. A single piece of equipment that
is not capable of performing Synchronous Ethernet breaks the chain. Ethernet
frames will still get through but downstream devices should not use the recovered
line timing because it will not be traceable to an acceptable stratum source.
6.5.1 Central Synchronization Subsystem
The timing subsystem has a central clock located on the CPM. The timing subsystem
performs several functions of the network element clock as defined by Telcordia
(GR-1244-CORE) and ITU-T G.781 standards.
The central clock uses the available timing inputs to train its local oscillator. The
number of timing inputs available to train the local oscillator varies per platform. The
priority order of these references must be specified. This is a simple ordered list of
inputs: (ref1, ref2, BITS (if available)).
The CPM clock output can drive the clocking for all line cards in the system. The
routers support selection of the node reference using Quality Level (QL) indications.
The recovered clock can derive its timing from one of the references available on that
platform.
The recovered clock can derive the timing from any of the following references (also
shown in Figure 24):

Nokia 7210 SAS-M Specifications

General

Brand	Nokia
Model	7210 SAS-M
Category	Cell Phone
Language	English