Configuring Synchronous Ethernet

Configuring Synchronous Ethernet
CH A P T E R
6
Configuring Synchronous Ethernet
The ME 3800X and ME 3600X switches support Synchronous Ethernet (SyncE), which is the PHY-layer
frequency-synchronization solution for IEEE 802.3 links. It is an evolution of the conventional Ethernet
and Ethernet + SDH and SONET-based synchronization. SyncE is used to synchronize and send clock
information to remote sites on the network. Each network element along the synchronization path must
support SyncE. SyncE provides only frequency synchronization, not related to time or space.
•
Understanding SyncE, page 6-1
•
Configuring SyncE, page 6-5
•
Monitoring SyncE, page 6-11
Understanding SyncE
SyncE provides a method to synchronize the Ethernet network by having all Ethernet ports send data
based on a reference clock. All devices supporting SyncE must send and receive data in cycles of fixed
size and duration. The data size depends on the Ethernet speed. The rate of transmission is 8000 cycles
per second. Each device must be able to support a system timing master, which is the synchronization
source. A sync port is the port on which synchronization information is received. All SyncE frames
coming from the sync port are the source of synchronization for all other ports on the device.
The switch 10 Gigabit Ethernet uplink ports or BITS interface support line clock recovery, sending and
receiving clock information. Downlink ports do not perform clock recovery and can only send clock
signals.
The switch supports TI (1544 kilobits/s) and E1 (2048 kb/s or 2048 KHz) clock timing synchronization.
•
Reference Clocks, page 6-1
•
SyncE Timing Using REP for Loop Prevention and Resiliency, page 6-2
•
BITS Interface, page 6-5
Reference Clocks
A switch comes up in a free-run state, using the internal oscillator (Stratum 3) for synchronization. If
there is a valid clock reference with a set priority, the switch locks to that reference. If there is no reliable
clock source available, the switch remains in free-run mode. If the current clock becomes invalid, the
switch goes into holdover mode and replays the saved clock from the last source. The switch SYNC
LEDs show the status of the internal clock: locked (green), free run (off), or in a holdover state (amber).
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Chapter 6
Configuring Synchronous Ethernet
Understanding SyncE
The reference clock source can be:
•
A Building Integrated Timing Supply (BITS) clock input
•
A PHY-recovered clock from uplink ports. The ME 3800X and 3600X switch supports a
PHY-recovered clock only from the small form-factor pluggable (SFP+) uplink ports with
10 Gigabit SFP+ or 1000BASE-X fiber SFP modules.
All uplink and downlink ports transmit data on the same reference clock.
The switch monitors each input clock for frequency accuracy and activity. An input clock with a
frequency out-of-band alarm or an activity alarm is invalid. Invalid clocks are not selected as the
reference clock.
During normal operation, the reference clock is selected based on an algorithm that uses the priority
rankings that you assign to the input clocks by using the network-clock-select priority priority global
configuration command. Priority 1 is the highest, and priority 15 is the lowest. If you try to assign the
same priority to more than one clock, error message appears. Unused input clocks are given a priority
value of 0, which disables the clocks and makes them unavailable for selection. The clock selection is
based on signal failure, priority, and manual configuration. If you have not manually configured a
reference clock, the algorithm selects the clock with the highest priority that does not experience signal
failure.
With this configuration, pure priority-based mode, an intermittent failure or changes in the network
topology can cause timing loops or a loss of connectivity with the clock reference. The Ethernet
Synchronous Messaging Channel (ESMC) with source-specific multicast (SSM) provides a way to
implement quality in synchronous networks, but this feature is not supported on the ME 3800X and
3600X switches. We recommend configuring the SyncE network as a Resilient Ethernet Protocol (REP)
segment for resiliency and to avoid timing loops when there are any network failures within the segment.
See “SyncE Timing Using REP for Loop Prevention and Resiliency” section on page 6-2
Reference clocks operate in revertive or nonrevertive mode, configured by using the
network-clock-select mode global configuration command.
•
In revertive mode, if an input clock with a higher priority than the selected reference becomes
available, the higher priority reference is immediately selected.
•
In nonrevertive mode, if an input clock with a higher priority becomes available, the higher-priority
clock is selected only when the current clock becomes invalid or unavailable.
You can use the set network-clocks privileged EXEC command to configure the input reference to be
either forced or automatically selected by the selection algorithm based on the highest priority valid
input clock. In revertive mode, the forced clock automatically becomes the selected reference. In
nonrevertive mode, the forced clock becomes the selected reference only when the existing reference is
invalidated or unavailable.
SyncE Timing Using REP for Loop Prevention and Resiliency
In pure priority-based mode, there is a risk of timing loops if the network topology changes. You can use
a REP workaround to avoid timing loops and to ensure timing resiliency. REP is a Cisco protocol used
to control network loops, to respond to link failures, and to improve convergence time. See Chapter 16,
“Configuring Resilient Ethernet Protocol.” REP controls a group of ports connected to each other in a
segment to ensure that the segment does not create any bridging loops and to respond to link failures
within the segment.
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Configuring Synchronous Ethernet
Understanding SyncE
A REP segment is a chain of ports connected to each other and configured with a segment identifier. Each
segment consists of standard (non-edge) ports and two user-configured edge ports. A switch can have no
more than two ports in the same REP segment and each segment port can have only one external
neighbor. REP is supported only on Layer 2 trunk interfaces.
You can use REP in the SyncE network with a REP no-edge segment or with REP VLAN load balancing.
You cannot configure SyncE as a REP segment and configure a BITS interface at the same time.
SyncE uses REP only for failure detection, and not for timing topology discovery or timing loop
prevention. These SyncE features are achieved through correct configuration of port priorities. Timing
loops can occur if priority is not correctly configured.
Configuring REP allows the segment to automatically respond to a failure in the ring and avoid timing
loops by changing the direction of the reference clock path. Figure 6-1 shows how you can configure a
REP segment in a SyncE network. The 10 Gigabit ports are used to connect the switches.
After you have configured switch network clock priority and configured the REP network, enter the
ql-enabled rep-segment segment-id command to identify the REP segment to with SyncE.
Figure 6-1
SyncE REP Segment
Switch 4
Priority 2
Router 1
Priority 1
Switch 3
REP Edge
Port
Priority 1
Priority 2
Blocked
Data path
Timing path
Router 2
Priority 2 Switch 1
281356
Priority 1
Clock
Reference
REP Edge
Port
Priority 2
Switch 2
Priority 1
Figure 6-2 shows a failure in the timing network, a broken link in the REP segment between Switch 4
and Router 1.
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Chapter 6
Configuring Synchronous Ethernet
Understanding SyncE
Figure 6-2
Broken Network Link
Priority 2
Switch 4
Router 1
Priority 1
Switch 3
REP Edge
Port
Priority 1
Priority 2
Blocked
Data path
Timing path
281357
Router 2
Priority 2 Switch 1
Priority 1
Clock
Reference
REP Edge
Port
Priority 2
Switch 2
Priority 1
Figure 6-3 shows how the REP segment handles the broken link to avoid timing loops in the SyncE
network.
Figure 6-3
SyncE REP Segment
Priority 2
Switch 4
Router 1
Priority 1
Switch 3
REP Edge
Port
Priority 1
Priority 2
Router 2
Priority 2 Switch 1
Data path
Timing path
281358
Priority 1
Clock
Reference
REP Edge
Port
Priority 2
Switch 2
Priority 1
When you configure the SyncE REP workaround, you can configure these SyncE features:
•
Hold-off timeout—If a clock source goes down, the switch holds the fail signal for a specific time
period before removing the source and restarting the synchronization process. Configure the
hold-off timeout by entering the network-clock-select hold-off timeout global configuration
command.
•
Wait-to-restore timeout—If a failed SyncE source comes up, the switch waits for a specific time
period of time before considering the source as available in the selection process. The default time
is 300 seconds. Configure wait-to-restore timeout by entering the network-clock-select
wait-to-restore global configuration command.
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Chapter 6
Configuring Synchronous Ethernet
Configuring SyncE
•
Holdover time or hold timeout—You can specify how long the switch replays the saved clock from
the last source if there is the clock source becomes unavailable before it moves from holdover state
to free run. Configure holdover time by using the network-clock-select hold-timeout global
configuration command. You can configure the time as infinite or as a range from 0 to 86,400
seconds.
When you do not configure REP with clock selection, the time is always infinite; the saved clock
replays forever. In pure priority-based mode, when the switch goes to holdover, it stays in this state
forever and does not transition to free-run state (even after the holdover value is exceeded and the
clock accuracy becomes like free run).
BITS Interface
The ME 3800X and ME 3600X switch supports a BITS interface through an RJ-45 connector. The
connection can be used for sending and receiving T1 and E1 timing signals.
You can configure all Ethernet ports to send data referenced to the BITS recovered clock. The BITS
signal is used as long as it does not have these faults:
•
loss of signal
•
out of frame
•
alarm-indication signal
•
remote alarm indication
The switch supports BITS IN and BITS OUT, and recovers and sends BITS timing, T1, E1, or
2.048 KHz. The switch does not support T1 or E1 data transmission. You can configure the BITS
interface input and output, including line coding and line buildout (output). You can also shut down the
BITS controller.
The switch supports these BITS configurations:
•
E1 Mode:
– 2048 KHz
– Framing mode: FAS, MFAS, FASCRC4, MFASCRC4 with line coding: AMI, HDB3
•
T1 Mode:
– Framing mode: D4 and ESF
– Line coding: AMI, B8ZS
– Line buildout (output): 0 to 133 feet, 133 to 266 feet, 266 to 399 feet, 399 to 533 feet, or 533 to
655 feet
Configuring SyncE
SyncE limitations on copper ports:
•
To receive clock data from an ME 3600X-TS 1 Gigabit Ethernet copper SFP interface, the link
partner must not be the 802.3 master port when 802.3 Clause 28 autonegotiation completes.
•
On ME3600X-FS or ME3800X switches, SyncE is not supported on 1 Gigabit Ethernet copper SFPs
for the first release.
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Chapter 6
Configuring Synchronous Ethernet
Configuring SyncE
•
Default SyncE Configuration, page 6-6
•
Configuring the Network Clock Selection, page 6-6
•
Configuring the BITS Interface, page 6-7
•
Selecting the Network Clock, page 6-9
•
Configuring REP for the SyncE Network, page 6-10
Default SyncE Configuration
Synchronous Ethernet is not configured on 10 Gigabit Ethernet interfaces.
1 Gigabit Ethernet interfaces transmit SyncE with no configuration required. No configuration is needed
to send clock timing in uplink or downlink interfaces.
Clock recovery is not configured on an uplink interface, which could be a 10 GigabitEthernet port or a
1 Gigabit- Ethernet fiber SFP.
Configuring the Network Clock Selection
Beginning in privileged EXEC mode, follow these steps to configure the SyncE network clock.
Command
Purpose
Step 1
configure terminal
Enter global configuration mode.
Step 2
network-clock-select priority {BITS | SYNCE port
number}
Configure the input clock and its priority.
•
For priority, the range is from 1 to 15, with 1 being
the highest priority and 15 the lowest. Unused input
clocks are given a priority value of 0.
•
BITS—Select the BITS port clock.
•
SYNCE—Select the Synchronous Ethernet clock.
•
For port number:
– Enter 0 for TenGigabitEthernet 0/1
– Enter 1 for TenGigabitEthernet 0/2
Step 3
network-clock-select output priority SYNCE port
Configure the 10 Gigabit Ethernet ports for SYNC output:
•
For priority, the range is from 1 to 15, with 1 being
the highest priority and 15 the lowest.
•
For port number:
– Enter 0 for TenGigabitEthernet 0/1
– Enter 1 for TenGigabitEthernet 0/2
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Configuring Synchronous Ethernet
Configuring SyncE
Step 4
Command
Purpose
network-clock-select mode {nonrevert | revert}
(Optional) Configure the reference switching mode to
determine the action to be taken if an input clock with a
higher priority than the selected reference becomes valid.
•
nonrevert—The new clock does not immediately
become valid but is selected only if the current
reference becomes invalid.
•
revert— The higher priority reference is
immediately selected as the reference clock. This is
the default.
Step 5
end
Return to privileged EXEC mode.
Step 6
show network-clocks
Verify the configuration.
Step 7
copy running-config startup config
(Optional) Save your entries in the switch startup
configuration file.
Enter the no network-clock-select priority or network-clock-select output to remove the selected
priority. Enter the no network-clock-select mode revert or the no network-clock-select mode
nonrevert to select the other mode.
This example configures the BITS clock with a priority of 2 and the SyncE input port as 10 Gigabit
Ethernet port 0/1 with the switching mode as nonrevertive.
Switch
Switch
Switch
Switch
(config)#
(config)#
(config)#
(config)#
network-clock-select priority 2 BITS
network-clock-select output 2 SYNCE 0
network-clock-select mode nonrevert
end
Configuring the BITS Interface
Beginning in privileged EXEC mode, follow these steps to configure the BITS interface. The Ethernet
Equipment Clock (EEC) mode of operation is based on the area of deployment.
Command
Purpose
Step 1
configure terminal
Enter global configuration mode.
Step 2
network-clock-select option {option1 | option2}
Configure the EEC option.:
•
option1—Select E1 as the input clock rate.
•
option2—Select T1 as the input clock rate
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Configuring SyncE
Step 3
Command
Purpose
controller BITS input applique E1 {2048KHz |
framing option linecode {ami | hdb3}
(Optional) Configure the controller BITS input framing
and coding options.
or
For E1 input:
controller BITS input applique T1 framing {d4 | esf}
linecode {ami | b8zs}
•
2048KHz—Select 2048 KHz input.
•
framing option—Select one of these options:
– fas_crc4—FASCRC4
– fas_nocrc—FAS
– mfas_crc4—MFASCRC4
– mfas_nocre—MFAS
For T1 input:
Step 4
•
d4 linecode—D4
•
esf linecode—Extended superframe
•
linecode ami—AMI encoding
•
linecode b8zs—B8ZS encoding
controller BITS output applique E1 {2048KHz |
framing options} linecode {ami | hdb3}
(Optional) Configure the controller BITS output framing
and coding options.
or
For E1 output:
controller BITS output applique T1 framing {d4 | esf}
linecode {ami | b8zs} line-build-out length
•
2048KHz—Select 2048 KHz input.
•
framing—Select one of these options:
– fas_crc4—FASCRC4
– fas_nocrc—FAS
– mfas_crc4—MFASCRC4
– mfas_nocre—MFAS
For T1 framing output:
•
d4 linecode—D4
•
esf linecode—Extended superframe
•
linecode ami—AMI encoding
•
linecode b8zs—B8ZS encoding
•
line-build-out length—Select a line length:
– 0-133ft
– 133-266ft
– 266-399ft
– 399-533ft
– 533-655ft
Step 5
controller BITS shutdown
Shut down the BITS controller.
Step 6
end
Return to privileged EXEC mode.
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Configuring SyncE
Command
Purpose
Step 7
show controller BITS
Verify the configuration.
Step 8
copy running-config startup config
(Optional) Save your entries in the switch startup
configuration file.
Enter the no network-clock-select mode option option 1 or the no network-clock-select mode option
option 2 to select the other option. mode with the default E1 or T1 values.
Use the no form of each command to remove the configuration or return to the default.
This example configures EEC as T1 with ESF framing, B8ZS line coding, and 1 to 133 foot.line buildout.
Switch (config)# network-clock-select option option2
Switch (config)# controller BITS input applique T1 framing esf linecode b8zs
Switch (config)# controller BITS output applique T1 framing esf linecode b8zs
line-build0-out 0-133ft
Switch (config)# end
Switch# show controllers BITS
Applique type is T1
Line Coding is B8ZS(Rx), B8ZS(Tx)
Framing is ESF(Rx), ESF(Tx)
Line Build Out is 0-133ft
No alarms detected.
Selecting the Network Clock
You can force selection of a particular network clock or select automatic clock selection where the
switch uses the selection algorithm based on the priority and the validity of the input.
Beginning in privileged EXEC mode, use this step to set the SyncE network clock.
Step 9
Command
Purpose
set network-clocks {automatic | force-reselect |
next-select}
Select one of these options:
•
automatic—Use the clock selection algorithm to
select the clock.
•
force-reselect—Force the system to select the valid
input clock with the highest priority and to always
keep this clock as the reference clock.
•
next-select—Force selection of the next valid input
clock with the highest priority.
If the switch is in nonrevertive mode, the clock input does
not change unless the current clock becomes invalid.
Step 10 show network-clocks
Verify the configuration.
Step 11 copy running-config startup config
(Optional) Save your entries in the switch startup
configuration file.
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Configuring Synchronous Ethernet
Configuring SyncE
Configuring REP for the SyncE Network
Beginning in privileged EXEC mode, use this procedure to configure a REP segment to avoid timing
loops when a failure occurs. In SynceE ring topologies, we recommend that you configure REP.
Command
Purpose
Step 1
configure terminal
Enter global configuration mode.
Step 2
network-clock-select priority SYNCE port number
Configure the input clock and its priority.
•
For priority, the range is from 1 to 15, with 1 being
the highest priority and 15 the lowest. Unused input
clocks are given a priority value of 0.
•
SYNCE—Select the Synchronous Ethernet clock.
•
For port number:
– Enter 0 for TenGigabitEthernet 0/1
– Enter 1 for TenGigabitEthernet 0/2
Step 3
rep administration vlan vlan-id
Specify the REP administrative VLAN. The range is 2 to
4094. The default is VLAN 1. To set the admin VLAN to
1, enter the no rep admin vlan global configuration
command.
Step 4
network-clock-select mode revert
(Optional) Configure the reference switching mode so
that if an input clock with a higher priority than the
selected reference becomes valid, the higher priority
clock is immediately selected. This is required in a ring
topology.
Step 5
ql-enabled rep-segment segment-id
Identify a REP segment to use for the REP workaround.
The segment-id range is from 1 to 1024.
Step 6
network-clock-select hold-off-timeout value
(Optional) Configure the time that a switch waits if a
clock source goes down before removing it as the
reference clock. The values are 0 or 50 to 10000 ms . The
default is 300 ms.
This command is valid only when SyncE is
configured with the REP workaround.
(Optional) Configure the time that the switch should
remain in holdover mode and replay the saved clock
information when no reliable clock source is available.
Note
Step 7
network-clock-select hold-timeout {value | infinite}
•
For value, the range is 0 to 86400 seconds.
•
Enter infinite for no timeout.
The default is infinite.
Step 8
network-clock-select wait-to-restore value
(Optional) Configure the time that a switch waits if a
failed SyncE interface comes back up before considering
the interface as a synchronization source.
The range is 0 to 720 seconds. The default is 300 seconds.
Note
This command is valid only when SyncE is
configured with the REP workaround.
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Monitoring SyncE
Step 9
Command
Purpose
show network-clocks
Verify the configuration.
Step 10 copy running-config startup config
(Optional) Save your entries in the switch startup
configuration file.
Use the no versions of the commands to disable the REP workaround segment selection or return to the
default settings.
This example configures the REP workaround and sets the clock input ports:
Switch
Switch
Switch
Switch
Switch
Switch
Switch
Switch
Switch
Switch
Switch
Switch
Switch
Switch
Switch
Switch
Switch
(config)# rep administrative vlan 2
(config)# network-clock-select output 2 SYNCE 0
(config)# interface tengigabitethernet 0/1
(config-if)# switchport mode trunk
(config-if)# rep segment 2
(config-if)# exit
(config)# ql-enabled rep-segment 3
(config)# network-clock-select 1 SYNCE 0
(config)# network-clock-select 2 SYNCE 1
(config)# interface tengigabitethernet 0/2
(config-if)# switchport mode trunk
(config-if)# rep segment 2
(config-if)# exit
(config)# network-clock-select mode revert
(config)# network-clock-select wait-to-restore-timeout 300
(config)# network-clock-select hold-off-timeout 300
(config)# end
Monitoring SyncE
Use these privileged EXEC commands to view SyncE configuration on a switch:
•
show controller BITS
Switch# show controller BITS
Applique type is T1
Line Coding is B8ZS(Rx), B8ZS(Tx)
Framing is ESF(Rx), ESF(Tx)
Line Build Out is 0-133ft
No alarms detected.
•
show network-clocks
Switch# show network-clocks
Network Clock Configuration
Input Clock BITS: valid
Input Clock SYNCE Te0/1: valid
Input Clock SYNCE Te0/2 : valid
System Clock Lock Status (T0DPLL) : Locked
Output Clock Generated from T4 DPLL
T4 DPLL Lock Status : Locked
System Clock Selected Ref: Te0/2
T4 DPLL Selected Ref: Te0/1
System Clock (T0 DPLL) Info:
Priority Source
Type
--------------------------------------------------------------01
Te0/2
SYNCE
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Monitoring SyncE
T4 DPLL Clock Info:
Priority Source
Type
--------------------------------------------------------------02
Te0/1
SYNCE
--------------------------------------------------------------System Clock Mode : Non Revertive
EEC Option Configured : Option 2
System Clock State is Automatic
--------------------------------------------------------------hold-timeout : infinite
ESMC/SSM workaround using REP not configured
--------------------------------------------------------------Measured offset freq for input BITS is +0.0ppm (3.8 ppm resolution)
Measured offset freq for input Te0/1 is +0.0ppm (3.8 ppm resolution)
Measured offset freq for input Te0/2 is +0.0ppm (3.8 ppm resolution)
Measured offset freq for current path (T4 DPLL) is +0.0ppm
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