Cisco ASR 1000 Series Aggregation Services Routers Software Configuration Guide, Cisco IOS XE 17
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IEEE 1588v2 Precision Time Protocol (PTP) is a packet-based two-way message exchange protocol for synchronizing clocks between
nodes in a network, thereby enabling an accurate time distribution over a network.This document explains how to configure
IEEE 1588v2 PTP on the Cisco ASR 1002-X Routers.
Restrictions for IEEE 1588v2 PTP
These are the restrictions for configuring IEEE 1588v2 PTP:
Supports IPv4 unicast mode, but not multicast mode.
Does not support Dot1q, Q-in-Q, and port-channel interfaces.
Primary PTP supports only a maximum of 32 secondary PTP.
PTP boundary clock is supported only in unicast negotiation mode.
IPv6 and Multiprotocol Label Switching (MPLS) encapsulation are not supported for PTP packet transfer over Cisco ASR 1002-X
Routers.
The time-of-day recovered from a 1588v2 session does not synchronize with the system clock.
GPS interfaces can be used only for clock recovery. You cannot transmit the system clock on the GPS interface.
Information About IEEE 1588v2 PTP
IEEE 1588v2 PTP is a packet-based two-way message exchange protocol for synchronizing a local
clock with a primary reference clock in a hierarchical primary-secondary architecture.
This synchronization is achieved through packets that are transmitted and received in a
session between a primary reference clock and a secondary clock. IEEE 1588v2 PTP
supports system-wide synchronization accuracy in the sub-microsecond range with little
use of network and local clock-computing resources.
The following sections describe the terminologies used for better understanding of the IEEE 1588v2 PTP.
PTP Clocks
PTP employs a hierarchy of clock types to ensure that precise timing and synchronization is maintained between the source
and the numerous PTP clients that are distributed throughout the network. A logical grouping of PTP clocks that synchronize
with each other using the PTP protocol, but are not necessarily synchronized to the PTP clocks in another domain, is called
a PTP domain.
The three PTP clock types are Ordinary clock, Boundary clock, and Transparent clock.
Ordinaryclock—This clock type has a single PTP port in a domain, and
maintains the timescale used in the domain. It may serve as a source of time, that
is, be a primary, or may synchronize to another clock by being a subordinate. It
provides time to an application or to an end device.
Boundaryclock—This clock type has multiple PTP ports in a domain, and
maintains the timescale used in the domain. It may serve as a source of time, that
is, be a primary, or may synchronize to another clock by being a subordinate. A
boundary clock, that is secondary, has a single slave port, and transfers timing
from that port to the primary ports.
Transparentclock—This clock type is a device that measures the time taken for a PTP event message to pass through the device, and provides
this information to the clocks receiving this PTP event message.
{start cross reference}Table 13-1{end cross reference} shows the 1588v2 PTP support matrix on a Cisco ASR1000 platform.
Table 1. 1588v2 PTP Support Matrix on a Cisco ASR1000 platform
Platform/PTP Clock mode
Ordinary Clock
Boundary Clock
Transparent Clock
Hybrid Clock
ASR1002X
Yes
Yes
No
No
Components of a
PTP-enabled Network
The three key components of a PTP-enabled data network are primary reference, PTP client, and
PTP-enabled router acting as a Boundary clock.
PrimaryReference—An IEEE1588v2 PTP network needs a primary reference
to provide a precise time source. The most economical way of obtaining the precise
time source for the primary reference is through a Global Positioning System (GPS)
because it provides +/- 100 nanosecond (ns) accuracy. First, the PTP primary
reference’s built-in GPS receiver converts the GPS timing information to PTP time
information, which is typically Coordinated Universal Time (UTC), and then delivers
the UTC time to all the PTP clients.
PTPclient—A PTP client has to be installed on
servers, network-monitoring and performance-analysis devices, or other devices
that want to use the precise timing information provided by PTP, and it’s
mostly an ordinary clock. The two kinds of PTP clients are pure software PTP
clients and hardware-assistant PTP clients.
PTPboundaryclock—Any router that is between a PTP primary and PTP
secondary can act as a PTP boundary clock router. It has two interfaces, one facing
the PTP primary and another facing the PTP secondary. The boundary clock router acts
as a secondary on the interface facing the PTP primary router , and
acts as a primary on the interface facing the PTP secondary router .
The PTP boundary clock router is deployed to minimize timing delay in cases where
the distance between PTP primary router and the PTP secondary router is more.
Note
Intermediary nodes between PTP primary and secondary should be a PTP-enabled or transparent
clock node.
The following figure
shows the functions of a PTP Enabled device.
Figure 1. 372860.eps
Functions of a PTP-Enabled Device
Clock-Synchronization Process
Clock synchronization is achieved through a series of messages exchanged between the primary
clock and the secondary clock as shown in the figure.
Figure 2. Clock-Synchronization Process
After the primary-secondary clock hierarchy is established, the clock synchronization process
starts. The message exchange occurs in this sequence:
The primary clock sends a Sync message. The time at
which the Sync message leaves the primary is time-stamped as t{start subscript}1{end
subscript}.
The secondary clock receives the Sync message and is time-stamped as t{start subscript}2{end
subscript}.
The secondary sends the Delay_Req message, which is time-stamped as t{start subscript}3{end
subscript} when it leaves the secondary, and as t{start subscript}4{end subscript}
when the primary receives it.
The primary responds with a Delay_Resp message that contains the time stamp t{start
subscript}4{end subscript}.
The clock offset is the difference between the primary clock and the secondary clock, and is
calculated as follows:
IEEE1588 assumes that the path delay between the primary clock and the secondary clock is
symmetrical, and hence, the mean path delay is calculated as follows:
All PTP communication is performed through message exchange. The two sets of messages defined by IEEE1588v2 are General messages
and Event messages.
Generalmessages—These messages do not require accurate time stamps, and are classified as Announce, Follow_Up, Delay_Resp, Pdelay_Resp_Follow_Up,
Management, and Signaling.
Eventmessages—These messages require accurate time stamping, and are classified as Sync, Delay_Req, Pdelay_Req, and Pdelay_Resp.
PTP Clocking Modes
The following are the PTP clocking modes supported on a Cisco ASR 1002-X Router:
UnicastMode—In unicast mode, the primary sends the Sync or
Delay_Resp messages to the secondary on the unicast IP address of the secondary,
and the secondary in turn sends the Delay_Req message to the primary on the
unicast IP address of the primary.
UnicastNegotiationMode—In unicast negotiation mode, the primary does not
know of any secondary until the secondary sends a negotiation message to the
primary. The unicast negotiation mode is good for scalability purpose because
one primary can have multiple secondary.
PTP Accuracy
Accuracy is an
important aspect of PTP implementation on an Ethernet port. For a packet
network, Packet Delay Variation (PDV) is one of the key factors that impacts
the accuracy of a PTP clock. The Cisco ASR 1002-X Router can handle the PDV of
the network with its advanced hardware and software capabilities, such as
hardware stamping and special high-priority queue for PTP packets. It can
provide around 300 ns accuracy in a scalable deployment scenario.
The two methods used
on the same topology to cross-check and verify the results are:
One-pulse-per-second (1PPS) to verify the secondary
PTP.
Maximum Time Interval Error (MTIE)
and Time Deviation (TDEV) to verify the PDV.
The verification topology includes a primary reference with a GPS receiver, a Cisco ASR 1002-X
Router, PTP hardware secondary reference clocks with 1PPS output, and a test equipment
for the measurement.
Figure 3. 1PPS Accuracy
Measurement
The following figure
shows the PPS accuracy, with time of day measured using the test equipment as
per the topology shown in the following figure. The average PPS accuracy value
found is 250 ns.
Figure 4. Graph Showing
PPS Accuracy
{start cross reference}Figure 13-5{end cross reference} shows a topology that includes a primary
reference with a GPS receiver, a Cisco ASR 1002-X Router, PTP hardware secondary
reference clocks, and a test equipment for the MTIE and TDEV measurement.
Figure 5. MTIE and TDEV
measurement
{start cross
reference}Figure 13-6{end cross reference} shows a graph with the MTIE and TDEV
measurements to verify the PDV.
Figure 6. Graph to show
MTIE and TDEV Measurement
IEEE 1588v2 PTP Support
IEEE 1588v2 PTP supports these features on a Cisco ASR1002-X Router:
Two-step Ordinary clock and Boundary clock.
Hardware-assistant PTP implementation to provide sub-300 ns accuracy.
PTP operation on all physical onboard Gigabit Ethernet interfaces.
Supports built-in Gigabit Ethernet links in two-step clock mode.
Configuring IEEE
1588v2 PTP
You can configure
IEEE 1588v2 PTP features on the Cisco ASR 1002-X Router by performing the
following procedures:
Configuring Input or
Output Network Clocking
We recommend that you configure a stable input clock source from a GPS device before configuring
primary PTP. The GPS device acts as a PTP primary reference, and the BITS or 10-MHz port
of a Cisco ASR 1002-X Router can be used to input or output the network clock. Perform
these tasks to configure network clocking on a Cisco ASR 1002-X Router:
Configuring an
Ordinary Clock
You can configure a Cisco ASR 1002-X Router in Ordinary clock mode as either primary or
secondary.
Figure 7. Ordinary Clock Scenario with a GPS Device as Primary Reference
Perform these tasks to configure an ordinary clock as either primary or secondary:
Configuring an Ordinary Clock as Primary PTP
This section describes how to configure an ordinary clock as primary PTP.
Specifies the IP version, transmission mode, and interface that a PTP clock port uses to exchange timing packets.
The negotiationkeyword specifies the unicast negotiation mode where the secondary
and primary clock exchange negotiation messages before establishing a
relationship.
Specifies the IP address of a PTP clock destination.
If the clock port is set to primary mode with unicast negotiation, you need not use this command
because the device uses negotiation to determine the IP address of PTP slave
devices.
Step 6
syncintervalinterval
Example:
Router(config-ptp-port)# sync interval -4
(Optional) Specifies the interval used to send PTP synchronization messages.
The default value is -5.
Step 7
end
Example:
Example:
Router(config-ptp-port)# end
Exits global configuration mode.
Examples
The following example shows how to configure an ordinary clock as primary PTP:
Specifies the IP version, transmission mode, and interface that a PTP clock port uses to exchange timing packets.
The negotiationkeyword specifies the unicast negotiation mode where the secondary
and primary clock exchanges negotiation messages before establishing a
relationship.
Note
Only Loopback interface type is supported.
Step 5
clocksourceip-address
Example:
Router(config-ptp-port)# clocksource10.10.10.10
Specifies the source IP address of a primary PTP clock.
Note
You can specify only 1 primary clock IP address. Priority-based clock source selection is not
supported.
Step 6
end
Example:
Router(config-ptp-port)# end
Exits global configuration mode.
Examples
The following example shows how to configure an ordinary clock as secondary PTP:
You can configure the primary PTP and secondary PTP in a boundary clock topology as shown in
the figure in the same way that you configure a primary and secondary in ordinary
clock mode. This section describes how to configure a Cisco ASR 1002-X Router in
boundary clock mode.
Note
Currently,
boundary clock supports only unicast negotiation mode.
Specifies the
IP version, transmission mode, and interface that a PTP clock port uses to
exchange timing packets.
The negotiationkeyword specifies the unicast negotiation mode where the secondary
and primary clock exchange negotiation messages before establishing a
relationship.
Note
Only
Loopback interface type is supported.
Step 5
clocksourceip-address
Example:
Router(config-ptp-port)# clocksource10.10.10.10
Specifies the
source IP address of a PTP master clock.
Note
You can specify only one primary clock IP address. Priority-based clock source selection
is not supported.
Step 6
exit
Example:
Router(config-ptp-port)# exit
Exits clock
port configuration mode.
Step 7
clock-port
name master
Example:
Router(config-ptp-clk)# clock-port MASTER master
Specifies the
clocking mode of a PTP port and enters clock port configuration mode.
Specifies the
IP version, transmission mode, and interface that a PTP clock port uses to
exchange timing packets.
The negotiationkeyword specifies the unicast negotiation mode where the secondary
and primary clock exchange negotiation messages before establishing a
relationship.
Note
Only
Loopback interface type is supported.
Step 9
end
Example:
Example:
Router(config-ptp-port)# end
Exits global
configuration mode.
Examples
The following example shows how to configure a boundary clock:
A Cisco ASR 1002-X
Router can exchange time of day and 1PPS input with an external device, such as
a GPS receiver, using the time of day and 1PPS input and output interfaces on
the router.
Perform these tasks
to configure Time of Day (ToD) messages on the Cisco ASR 1002-X Router:
Configuring Input Time-of-Day Messages
This section describes how to configure input time-of-day messages.
Note
You can configure time-of-day input only in a primary PTP clock port.
Specifies the IP version, transmission mode, and interface that a PTP clock port uses to exchange timing packets.
The negotiationkeyword specifies the unicast negotiation mode where the secondary
and primary clock exchange negotiation messages before establishing a
relationship.
Specifies the IP address of a PTP clock destination.
If the clock port is set to primary mode with unicast negotiation, you need not use this command
because the device uses negotiation to determine
the IP address of secondary PTP devices.
Step 8
end
Example:
Router(config-ptp-port)# end
Exits global configuration mode.
What to do next
Examples
The following example shows how to configure input time-of-day messages:
Specifies the IP version, transmission mode, and interface that a PTP clock port uses to exchange timing packets.
The negotiationkeyword specifies the unicast negotiation mode where the secondary
and primary clock exchange negotiation messages before establishing a
relationship.
Note
Only Loopback interface type is supported.
Step 7
clocksourceip-address
Example:
Router(config-ptp-port)# clocksource10.10.10.10
Specifies the source IP address of a PTP master clock.
Note
You can specify only 1 primary clock IP address. Priority-based clock source selection is not
supported.
Step 8
end
Example:
Example:
Router(config-ptp-port)# end
Exits global configuration mode.
What to do next
Examples
The following example shows how to configure output time-of-day messages:
Use the following commands to verify the IEEE 1588v2 PTP configuration:
Use the showptpclockrunningdomain0command to display the output:
Router# show ptp clock running domain 0
On the MASTER:
PTP Ordinary Clock [Domain 0]
State Ports Pkts sent Pkts rcvd Redundancy Mode
FREQ_LOCKED 1 31522149 10401171 Hot standby
PORT SUMMARY
PTP Master
Name Tx Mode Role Transport State Sessions Port Addr
MASTER unicast master Lo1 Master 1 -
SESSION INFORMATION
MASTER [Lo1] [Sessions 1]
Peer addr Pkts in Pkts out In Errs Out Errs
11.11.11.11 10401171 31522149 0 0
On the SLAVE:
PTP Ordinary Clock [Domain 0]
State Ports Pkts sent Pkts rcvd Redundancy Mode
PHASE_ALIGNED 1 4532802 13357682 Track one
PORT SUMMARY
PTP Master
Name Tx Mode Role Transport State Sessions Port Addr
SLAVE unicast slave Lo20 Slave 1 10.10.10.10
SESSION INFORMATION
SLAVE [Lo20] [Sessions 1]
Peer addr Pkts in Pkts out In Errs Out Errs
10.10.10.10 13357682 4532802 0 0
Use the showplatformsoftwareptptodcommand to check the time-of-day information:
PTPd ToD information:
Time: 06/24/14 02:06:29
Use the showplatformptptodallcommand to check the time-of- day state:
Router# show platform ptp tod allOn the MASTER
--------------------------------
ToD/1PPS Info for : R0
--------------------------------
RJ45 JACK TYPE : RS422
ToD CONFIGURED : YES
ToD FORMAT : NTPv4
ToD DELAY : 0
1PPS MODE : INPUT
1PPS STATE : UP
ToD STATE : UP
--------------------------------
On the SLAVE:
--------------------------------
ToD/1PPS Info for : R0
--------------------------------
RJ45 JACK TYPE : RS422
ToD CONFIGURED : YES
ToD FORMAT : NTPv4
ToD DELAY : 0
1PPS MODE : OUTPUT
OFFSET : 0
PULSE WIDTH : 0
--------------------------------
Additional References
MIBs
MIB
MIBs Link
None
To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at this
URL:
The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use
these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products
and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password.
{start cross reference}Table 13-2{end cross reference} lists the features in this module and provides links to specific configuration
information.
Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator
enables you to determine which software images support a specific software release, feature set, or platform. To access Cisco
Feature Navigator, go to {start hypertext}http://www.cisco.com/go/cfn{end hypertext}. An account on Cisco.com is not required.
Note
{start cross reference}Table 13-2{end cross reference} lists only the software release that introduced support for a given
feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also
support that feature.
Table 2. Feature Information for Network Synchronization Support
Feature Name
Releases
Feature Information
IEEE 1588v2 PTP Support
Cisco IOS XE 3.13S
In Cisco IOS XE Release 3.13S, this feature was introduced on the Cisco ASR 1002-X Routers.