Example: Configuring Centralized Clocking on the Enhanced MX Switch Control Board
These examples show how to configure the following clock sources and features on an Enhanced MX Switch Control Board (SCB): Synchronous Ethernet, ordinary Precision Time Protocol (PTP) slave, hybrid PTP slave, and retiming through the building-integrated timing supply (BITS) external interface.
Requirements
These examples use the following hardware and software components:
- One MX240, MX480, or MX960 router with MPC 16x10GE or MPC2Es (see MPCs Supported by MX240, MX480, and MX960 Routers) for Synchronous Ethernet clock sources, or MPC2E-P for PTP clock sources
- One Synchronous Ethernet clock source device (may be an MX240, MX480, or MX960 router)
- One PTP grandmaster device
- One BITS device (may be the same as the PTP grandmaster device)
- Junos OS Release 12.2 or later for MX240, MX480, or MX960 routers
- Junos OS Release 12.3 or later to configure a BITS interface as an input, output, or I/O clock source for MX240, MX480, or MX960 routers
Before you begin configuring centralized clocking on an interface that uses Synchronous Ethernet, ensure that you have configured the MX Series interface as a chassis synchronization source to the device that provides a Synchronous Ethernet clock source.
- Configure the MX Series interface as a chassis synchronization source to the device that provides a Synchronous Ethernet clock source.
Overview
With the addition of a Stratum 3 (ST3) clock module to the Enhanced MX SCB, an MX240, MX480, or MX960 chassis can perform clock monitoring, filtering, and holdover in a centralized chassis location. Chassis line cards can be configured to recover network timing clocks at the physical layer via Synchronous Ethernet or by a packet-based PTP implementation. These recovered clocks are routed to the Enhanced MX SCB ST3 clock module via the chassis backplane. A clock selection algorithm is run that selects the best quality recovered clock from the list of configured clock sources. The ST3 clock module locks to the selected clock source and fans it out to the chassis line cards. 16x10GE 3D and MPC2Es (see MPCs Supported by MX240, MX480, and MX960 Routers) can distribute this clock to downstream network elements via Synchronous Ethernet.
The ST3 clock module acquires holdover data while locked to the selected clock source. If the clock fails, the ST3 clock module enters holdover mode and replays collected holdover data to maintain its output clock. The ST3 holdover performance depends on the drift of the Enhanced MX SCB OCXO device.
In Junos 12.3, support was added for synchronizing an MX240, MX480, or MX960 chassis with an Enhanced MX SCB to a BITS timing source through an RJ-48 port on the Enhanced MX SCB. The BITS external clock interface (ECI) supports the sending and receiving of Synchronization Status Message (SSM) quality levels. The quality level is used by the chassis clock-selection algorithm. When BITS output is configured, the source-mode default is the selected line clock source.
The BITS external interface can be connected to a retiming device, which cleans up the clock and sends it back in the external BITS interface. The conditioned input BITS clock is selected as the chassis clock and distributed downstream via Synchronous Ethernet interfaces. The tx-dnu-to-line-source-enable option is used to prevent a timing loop. Figure 1 shows the BITS retiming functionality using a Synchronization Supply Unit (SSU). For instructions on how to configure retiming through the BITS external interface, see Configuring Retiming through the BITS External Interface.
Figure 1: BITS Retiming with Synchronization Supply Unit (SSU)
Prior to the Enhanced MX SCB, clock monitoring, filtering, and holdover functions were distributed throughout the chassis and performed on MPC2E line cards. This distributed clocking mode limits the distribution of timing to downstream network elements on MPC2E interfaces only. Centralized clocking mode removes this limitation by supporting the distribution of timing on MPC 16x 10GE line interfaces as well.
Configuration
To configure centralized clocking, perform one or more of these tasks:
- Configuring Centralized Clocking from a Synchronous Ethernet Clock Source
- Configuring Centralized Clocking from an Ordinary PTP Clock Source
- Configuring Centralized Clocking from a Hybrid PTP Clock Source
- Configuring Retiming through the BITS External Interface
Configuring Centralized Clocking from a Synchronous Ethernet Clock Source
CLI Quick Configuration
To quickly configure this example, copy the following commands, paste them into a text file, remove any line breaks, change any details necessary to match your network configuration, and then copy and paste the commands into the CLI at the [edit] hierarchy level.
Step-by-Step Procedure
The following example requires you to navigate various levels in the configuration hierarchy. For instructions on how to do that, see Using the CLI Editor in Configuration Mode in the CLI User Guide.
To configure a Synchronous Ethernet clock source:
- Configure the network option:[edit chassis synchronization]user@host# set network-option option-2
- Configure the priority and quality level of the clock
source on this interface:[edit chassis synchronization source interfaces ge-4/1/0]user@host# set priority 1user@host# set quality-level st3
Results
From configuration mode, confirm your configuration by entering the show chassis synchronization command. If the output does not display the intended configuration, repeat the configuration instructions in this example to correct it.
[edit]
user@host# show chassis synchronization
network-option option-2;
source {
interfaces ge-4/1/0 {
priority 1;
quality-level st3;
}
}
After you configure the device, enter commit from configuration mode.
Configuring Centralized Clocking from an Ordinary PTP Clock Source
Step-by-Step Procedure
To configure a PTP clock source:
- Configure ordinary mode PTP on the ge-4/1/9 interface to the PTP grandmaster device. See Example: Configuring Precision Time Protocol.
Configuring Centralized Clocking from a Hybrid PTP Clock Source
CLI Quick Configuration
To quickly configure this example, copy the following commands, paste them into a text file, remove any line breaks, change any details necessary to match your network configuration, and then copy and paste the commands into the CLI at the [edit] hierarchy level.
Step-by-Step Procedure
The following example requires you to navigate various levels in the configuration hierarchy. For instructions on how to do that, see Using the CLI Editor in Configuration Mode in the CLI User Guide.
To configure a hybrid PTP clock source:
- Configure the network option:[edit chassis synchronization]user@host# set network-option option-2
- Configure the priority and quality level of the clock
source on this interface:[edit chassis synchronization source interfaces ge-4/1/0]user@host# set priority 1user@host# set quality-level st3
- Configure hybrid mode PTP on the ge-4/1/9 interface to the PTP grandmaster device. For the synchronous-ethernet-mapping interface, specify the Synchronous Ethernet interface used in Step 2.
Results
From configuration mode, confirm your configuration by entering the show chassis synchronization command. If the output does not display the intended configuration, repeat the configuration instructions in this example to correct it.
[edit]
user@host# show chassis synchronization
network-option option-2;
source {
interfaces ge-4/1/0 {
priority 1;
quality-level st3;
}
}
After you configure the device, enter commit from configuration mode.
Configuring Retiming through the BITS External Interface
CLI Quick Configuration
To quickly configure this example, copy the following commands, paste them into a text file, remove any line breaks, change any details necessary to match your network configuration, and then copy and paste the commands into the CLI at the [edit] hierarchy level.
Step-by-Step Procedure
The following example requires you to navigate various levels in the configuration hierarchy. For instructions on how to do that, see Using the CLI Editor in Configuration Mode in the CLI User Guide.
To configure retiming through the BITS external interface using an SSU:
- Configure the network option (G.812 type IV clock):[edit chassis synchronization]user@host# set network-option option-2
- Configure the external BITS signal type (T1-coded 1.544-MHz
signal on 100-ohm balanced line):[edit chassis synchronization interfaces external]set signal-type t1
- Configure the external BITS signal line-encoding (B8ZS)
and framing (superframe) options:[edit chassis synchronization interfaces external]user@host# set t1-options line-encoding b8zsuser@host# set t1-options framing sf
- Configure the output external BITS signal properties:
- Disable wander filtering:[edit chassis synchronization output interfaces external]user@host# set wander-filter-disable
- Disable holdover:[edit chassis synchronization output interfaces external]user@host# set holdover-mode-disable
- Select the best line clock source for output:[edit chassis synchronization output interfaces external]user@host# set source-mode line
- Set Tx QL to DNU/DUS on the line source interface to prevent
a timing loop:[edit chassis synchronization output interfaces external]user@host# set tx-dnu-to-line-source-enable
- Set minimum quality level:[edit chassis synchronization output interfaces external]user@host# set minimum-quality st3
- Disable wander filtering:
- Configure the incoming clock source and quality level:[edit chassis synchronization source interfaces ge-4/0/1]user@host# set quality-level st3
- Configure the external clock source and quality level:[edit chassis synchronization source interfaces external]user@host# set quality-level prs
Results
From configuration mode, confirm your configuration by entering the show chassis synchronization command. If the output does not display the intended configuration, repeat the configuration instructions in this example to correct it.
[edit]
user@host# show chassis synchronization
network-option option-2;
interfaces external {
signal-type t1;
t1-options {
line-encoding b8zs;
framing sf;
}
}
output {
interfaces external {
wander-filter-disable;
holdover-mode-disable;
source-mode line;
tx-dnu-to-line-source-enable;
minimum-quality st3;
}
}
source {
interfaces ge-4/0/1 {
quality-level st3;
}
interfaces external {
quality-level prs;
}
}
After you configure the device, enter commit from configuration mode.
Verification
Confirm that the configuration is working properly.
- Verifying the Synchronous Ethernet Clock Source
- Verifying the Ordinary PTP Clock Source
- Verifying the Hybrid PTP Clock Source
- Verifying the Retiming through the BITS External Interface
Verifying the Synchronous Ethernet Clock Source
Purpose
Verify that the MX Series router recovers, selects, qualifies, and locks to the configured Synchronous Ethernet clock source.
Action
From operational mode, enter the show chassis synchronization clock-module command.
user@host> show chassis synchronization clock-module
Clock module on SCB0
Current role : master
Current state : locked to ge-4/1/0
State for : 0 days, 00 hrs, 00 mins, 15 secs
State since : Mon Jun 6 07:28:47 2011
Monitored clock sources
Interface Type Status
ge-4/1/0 syncE qualified-selected
Meaning
The Monitored clock sources field shows that the ge-4/1/0 interface has the Synchronous Ethernet type and is the qualified and selected centralized clock source.
Verifying the Ordinary PTP Clock Source
Purpose
Verify that the MX Series router recovers, selects, qualifies, and locks to the configured PTP clock source.
Action
From operational mode, enter the show chassis synchronization clock-module command.
user@host> show chassis synchronization clock-module
Clock module on SCB0
Current role : master
Current state : locked to ge-4/1/9
State for : 0 days, 00 hrs, 00 mins, 45 secs
State since : Wed Jun 29 10:52:05 2011
Monitored clock sources
Interface Type Status
ge-4/1/9 ptp qualified-selected
Meaning
The Monitored clock sources field shows that the ge-4/1/9 interface has the ptp type and is the qualified and selected centralized clock source.
Verifying the Hybrid PTP Clock Source
Purpose
Verify that the MX Series router recovers, selects, qualifies, and locks to the configured hybrid PTP clock source.
Action
From operational mode, enter the show chassis synchronization clock-module command.
user@host> show chassis synchronization clock-module
Clock module on SCB0
Current role : master
Current state : locked to ge-4/1/9
State for : 0 days, 00 hrs, 00 mins, 15 secs
State since : Wed Jun 29 11:19:25 2011
Monitored clock sources
Interface Type Status
ge-4/1/9 ptp-hybrid qualified-selected
Configured sources:
Interface : ge-4/1/0
Status : Primary Index : 218
Clock source state : Clk qualified Priority : 1
Configured QL : ST3 ESMC QL : DUS
Clock source type : ifd Clock Event : Clock locked
Kernel flags : Up,sec,
Meaning
The Monitored clock sources field shows that the ge-4/1/9 interface has the ptp-hybrid type and is the qualified and selected centralized clock source. The Configured sources field shows that the ge-4/1/0 interface has the Clock locked Clock Event .
Verifying the Retiming through the BITS External Interface
Purpose
Verify that the MX Series router recovers, selects, qualifies, and locks to the configured clock source, and that the external clock is locked to the configured clock source.
Action
From operational mode, enter the show chassis synchronization extensive command.
user@host> show chassis synchronization extensive Current clock status : Locked Clock locked to : Primary Configured interfaces: Name : external Signal type : t1 (sf b8zs) Rx status : active Tx status : active LED color : green Configured outputs: Interface : external Tx status : active Minimum QL : ST3 Tx QL : ST3 Holdover mode : disabled Wander filter : disabled Source mode : line Source Tx DNU : enabled Holdover data : valid Current state : locked to ge-4/0/1 State for : 0 days, 00 hrs, 24 mins, 47 secs State since : Thu Sep 6 13:01:07 2012 Configured sources: Interface : external Status : Primary Index : 0 Clock source state : Clk qualified Priority : Default(6) Configured QL : PRS ESMC QL : PRS Clock source type : extern Clock Event : Clock locked Interface State : Up,pri, Interface : ge-4/0/1 Status : Secondary Index : 152 Clock source state : Clk qualified Priority : Default(8) Configured QL : ST3 ESMC QL : DUS Clock source type : ifd Clock Event : Clock qualified Interface State : Up,sec,ESMC TX(QL DUS/SSM 0xf),
Meaning
The Configured interfaces field shows that the external interface receive and transmit statuses are active. The Configured outputs field shows that the current state is locked to ge-4/0/1. The Configured sources field shows that the external interface is the qualified and selected centralized clock source, and has the Clock locked Clock Event. The Configured sources field shows that the ge-4/0/1 interface is the secondary clock source, and has the Clock qualified Clock Event.
