| Description | Network clock status and statistics for sources of network
clock identified by entPhysicalIndex and used by the managed
system when the value of cncDistributionMethod is 'ncdp'.
A source of network clock for the device may be an
oscillator local to the device, a Building Integrated Timing
Supply (BITS) port or an interface that supports synchronous
clock recovery.
(BITS is explained in more detail in Bell Communications
Research, GR-436-CORE, 'Digital Network Synchronization
Plan'.)
The NCDP protocol entity selects one entry in this table to
advertise as the best available clock source for the device.
Cooperating NCDP protocol entities select the best available
clock source among those advertised within the cooperating
group and build a clock distribution tree rooted at that
clock source. When the value of cncRootClockSource is used
as an index into this table and the indicated clock source
has cncNcdpBestClockSource with value 'true' then the
indicated clock source is the root of some clock
distribution tree. If only one such root exists on all
participating devices in the network, then it is the root of
a network wide clock distribution tree.
When the managed system initializes it creates a row for the
device's default source of network clock. This row cannot be
destroyed by a management station. Within this row a write
operation is only allowed on the cncNcdpPriority object; only
read operations are allowed on all other columnar objects
within this specific row. The status of this row is always
active. The default source can always be found by issuing a
read operation on the row within cncManualSourceTable indexed
by 'default' (as the value of cncManualSourcePriority). The
cncManualSourceId object contains the entPhysicalIndex of the
default source of network clock and identifies it within this
table.
Other rows are created or destroyed by a management station
or through the device's local management interface when a
source of network clock is configured or removed. When a
management station creates a row it creates it explicitly
using RowStatus with either createAndGo or createAndWait.
A row is not made active until all read-create objects not
having default values are properly initialized.
The values of cncNcdpPriority, cncNcdpStratum and
cncNcdpPRSReference collectively describe a source of network
clock, that is they are three components of a vector used as
an input to the NCDP algorithm to make clock source selection
decisions. The management station must make the row
notInService before changing the values of any of these
objects. |