To name a source to provide timing for the network clock and to specify the selection priority for this clock source, use
the
network -clock
select command in global configuration mode. To cancel the network clock selection, use the
no form of this command.
Cisco ASR 1000 Series
network-clock select {priority [bits [R0 | R1] {e1 [crc4 | no-crc4 | unframed] | t1 [esf | sf | unframed]} | controller type number | global | interface type number | local | system] | option {1 | 2}}
no network-clock select priority [global | local]
Cisco 7600 Series and Cisco 10000 Series
network-clock select priority {controller type number | interface type number | slot number | system} [global | local]
no network-clock select priority [global | local]
Syntax Description
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priority
|
Selection priority for the clock source (1 is the highest priority). The range is 1 to 6.
The clock with the highest priority is selected to drive the system time division multiplexing (TDM) clocks. When the higher-priority
clock source fails, the next-higher-priority clock source is selected.
|
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bits
|
(Optional) Derives network timing from the central office (CO) Building Integrated Timing Supply (BITS) clock.
|
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R0
|
(Optional) Specifies Route Processor 0 BITS as the source slot.
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R1
|
(Optional) Specifies Route Processor 1 BITS as the source slot.
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e1
|
(Optional) Configures the BITS interface to use an E1 connection.
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crc4
|
(Optional) Configures the E1 BITS interface framing with Cyclic Redundancy Check 4 (CRC4).
|
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no-crc4
|
(Optional) Configures the E1 BITS interface framing with no CRC4.
|
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unframed
|
(Optional) Configures the BITS interface with clear channel.
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t1
|
(Optional) Configures the BITS interface to use a T1 connection.
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esf
|
(Optional) Configures the T1 BITS interface with the Extended Super Frame (ESF) framing standard.
|
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sf
|
(Optional) Configures the T1 BITS interface with the Super Frame (SF) framing standard.
|
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controller
type
number
|
Specifies the controller to be the clock source.
|
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interface
type
number
|
Specifies the interface to be the clock source.
|
|
slot
number
|
Specifies the slot to be the clock source. The range is 1 to 6.
|
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global
|
(Optional) Configures the source as global.
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local
|
(Optional) Configures the source as local.
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system
|
Specifies the system clock as the clock source.
|
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option
|
Specifies the standards for the network option. The applicable values are as follows:
- 1—Network option I is the ITU G-813 standard.
- 2—Network option II (Gen1) is the Bellcore GR-1244/GR-253 (stratum 3) and ITU G-813 standard. This is the default value.
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Note
|
The network options are available only in the RP2 platform.
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Command Default
The router uses the system clock (also called free-running mode).
Note
|
Because default clock values are derived from an external source, they can fall outside the configurable range.
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Command Modes
Global configuration (config)
Command History
|
Release
|
Modification
|
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11.3 MA
|
This command was introduced on the Cisco MC3810.
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12.0(3)XG
|
The BVM as a possible network clock source was added.
|
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12.1(5)XM
|
This command was implemented on the Cisco 3660. The keywords
t1 and
e1 were introduced.
|
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12.2(4)T
|
This command was integrated into Cisco IOS Release 12.2(4)T.
|
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12.2(2)XB
|
This command was implemented on the Cisco 2600 series and Cisco 3660 with AIMs installed.
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12.2(8)T
|
This command was integrated into Cisco IOS Release 12.2(8)T.
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12.2(15)T
|
This command was implemented on the Cisco 2600XM, Cisco 2691, Cisco 3725, and Cisco 3745.
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12.3(8)T4
|
This command was integrated into Cisco IOS Release 12.3(8)T4 and the
bri keyword was added. Support was also added for the Cisco 2800 series.
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12.3(11)T
|
This command was integrated into Cisco IOS Release 12.3(11)T and the
atm keyword was added. Support was also added for the Cisco 3800 series.
|
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Cisco IOS XE Release 2.1
|
This command was introduced in a release earlier than Cisco IOS Release 2.1.
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15.0(1)S
|
This command was integrated into a release earlier than Cisco IOS Release 15.0(1)S.
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Cisco IOS XE Release 3.1
|
This command was modified. This command was implemented on the Cisco ASR 1000 platform. The
option keyword was added.
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Usage Guidelines
When an active clock source fails, the system chooses the next-lower-priority clock source that is specified by this command.
When a higher-priority clock source becomes available, the system automatically reselects it.
You can specify up to five clock priorities. The highest-priority active interface in the router supplies the primary reference
source to all other interfaces that require network clock synchronization services.
For timing sources, the Route Processor can receive timing information through its BITS interface or through a TDM-based
Shared Port Adapter (SPA). For some telecommunications deployments, BITS clocking is required to provide global clocking synchronization
of network equipment in the end-to-end data path. A BITS clock can be supplied to the network clock module using a T1 or E1
connection.
If a controller is specified in the clock source hierarchy, you must configure that controller for line timing (by using
the appropriate
clock
source
line command for the controller). Any controller that is not currently acting as the clock source will automatically operate in
loop timing mode. Both controllers can be given different clock source priority values. For more information, see the
Cisco IOS Interface and Hardware Component Command Reference .
Note
|
To minimize backplane clock shifts, the
no
network-clock
select command does not take effect until you return to EXEC mode by entering
exit or
end . This process minimizes the number of times that clock sources are configured.
|
Use the
show
network-clocks command to display clock priorities that are configured on the router.
Examples
The following example shows how to configure the network clock as revertive and assign clock sources to two priorities:
Router> enable
Router# configure terminal
Router(config)# network-clock revertive
Router(config)# network-clock select 1 bits R0 e1
Router(config)# network-clock select 2 interface GigabitEthernet 0/0/1
The following example shows how to configure the network option for network clock.
Router(config)#
network-clock
select
option
1
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