User guide

3-16
Configuration Guide for Cisco DSLAMs with NI-2
OL-2074-03
Chapter 3 Initially Configuring the Cisco DSLAM
Configuring Network Clocking
Note By default, the network clock is nonrevertive. Nonrevertive means that once a network clock source fails
and the DSLAM switches to the clock source with the next highest priority, manual intervention is
required to force the DSLAM to switch back to a higher-priority clock source. The algorithm to switch
to the highest priority best clock only runs if you configure the network-clock-select command as
revertive.
Figure 3-4 Transmit Clocking Priority Configuration Example
These sections describe network clocking:
• Configuring Network Clock Priorities and Sources, page 3-16
• Configuring the Transmit Clocking Source, page 3-17
• Providing Clock Synchronization Services, page 3-18
Configuring Network Clock Priorities and Sources
To configure the network clocking priorities and sources, use the following commands in global
configuration mode:
DSLAM #1 DSLAM #2
Reference clock
source
ATM 0/1
ATM 0/2
(Priority 1TX
clock source)
Reference clock signal
(Priority 2 TX clock
source)
TX
Data
Primary Clocking
Secondary Clocking
27156
Command Task
DSLAM(config) network-clock-select priority
{BITS | system | atm slot/port}
Configure the priority of a timing source. Priority
values are 1 to 4.
DSLAM(config) network-clock-select BITS
{T1 | E1} margin}
Configure the type and margin, in decibels, of the
BITS line for a T1 or an E1 line. Margin values vary
according to the length of the T1 or E1 line.
DSLAM(config) network-clock-select
revertive
Configure the system to revert to a higher priority
timing source when it becomes available.