Overview
The Precision Time Protocol (PTP), as defined in the IEEE 1588 standard, synchronizes with nanosecond accuracy the real-time clocks of the devices in a network. The clocks are organized into a master-slave hierarchy. PTP identifies the port that is connected to a device with the most precise clock. This clock is referred to as the master clock. All the other devices on the network synchronize their clocks with the master and are referred to as members. Constantly-exchanged timing messages ensure continued synchronization. PTP ensures that the best available clock is selected as the source of time (the grandmaster clock) for the network and that other clocks in the network are synchronized to the grandmaster.
Network Element |
Description |
---|---|
Grandmaster (GM) |
A network device physically attached to the primary time source. All clocks are synchronized to the grandmaster clock. |
Ordinary Clock (OC) |
An ordinary clock is a 1588 clock with a single PTP port that can operate in one of the following modes:
|
Boundary Clock (BC) |
The device participates in selecting the best master clock and can act as the master clock if no better clocks are detected. Boundary clock starts its own PTP session with a number of downstream slaves. The boundary clock mitigates the number of network hops and results in packet delay variations in the packet network between the Grand Master and Slave. |
Transparent Clock (TC) |
A transparent clock is a device or a switch that calculates the time it requires to forward traffic and updates the PTP time correction field to account for the delay, making the device transparent in terms of time calculations. |
PTP consists of two parts:
-
The port State machine and Best Master Clock Algorithm: This provides a method to determine the ports in the network that will remain passive (neither master nor slave), run as a master (providing time to other clocks in the network), or run as slaves (receiving time from other clocks in the network).
-
Delay-Request/Response mechanism and a Peer-delay mechanism: This provides a mechanisms for slave ports to calculate the difference between the time of their own clocks and the time of their master clock.
Note
Cisco ASR 9000 Series routers do not support Peer-delay mechanism.
The implementation of PTP on Cisco IOS XR software is designed to operate effectively in Telecommunication networks, which are different from the networks for which PTP was originally designed.
PTP is configurable on Gigabit Ethernet interfaces (1G, 10G, 40G, and 100G), Bundle Ethernet interfaces, and sub-interfaces. PTP is not configurable on LAG Ethernet sub-interfaces.
Frequency and Time Selection
The selection of the source to synchronize the backplane clock frequency is made by frequency synchronization, and is outside of the scope of PTP. The Announce, Sync, and Delay-request frequencies must be the same on the master and slave.
Delay-Response Mechanism
The Delay Request-response mechanism (defined in section 11.3 of IEEE Std 1588-2008) lets a slave port estimate the difference between its own clock-time and the clock-time of its master. The following options are supported:
-
One-step mechanism - The timestamp for a Sync message is sent in the Sync message itself.
-
Two-step mechanism - The timestamp for a Sync message is sent later in a Follow-up message.
When running a port in Slave state, a router can send Delay-request messages and handle incoming Sync, Follow-up, and Delay-response messages. The timeout periods for both Sync and Delay-response messages are individually configurable.
Hybrid Mode
Your router allows the ability to select separate sources for frequency and time-of-day (ToD). Frequency selection can be between any source of frequency available to the router, such as: BITS, GPS, SyncE or IEEE 1588 PTP. The ToD selection is between the source selected for frequency and PTP, if available (ToD selection is from GPS, DTI or PTP). This is known as hybrid mode, where a physical frequency source (BITS or SyncE) is used to provide frequency synchronization, while PTP is used to provide ToD synchronization.
Frequency selection uses the algorithm described in ITU-T recommendation G.871, and is described in the Configuring Frequency Synchronization module in this document. The ToD selection is controlled using the time-of-day priority configuration. This configuration is found under the source interface frequency synchronization configuration mode and under the global PTP configuration mode. It controls the order for which sources are selected for ToD. Values in the range of 1 to 254 are allowed, with lower numbers indicating higher priority.
Port States
State machine indicates the behavior of each port. The possible states are:
State |
Description |
---|---|
INIT |
Port is not ready to participate in PTP. |
LISTENING |
First state when a port becomes ready to participate in PTP: In this state, the port listens to PTP masters for a (configurable) period of time. |
PRE-MASTER |
Port is ready to enter the MASTER state. |
MASTER |
Port provides timestamps for any Slave or boundary clocks that are listening. |
UNCALIBRATED |
Port receives timestamps from a Master clock but, the router’s clock is not yet synchronized to the Master. |
SLAVE |
Port receives timestamps from a Master clock and the router’s clock is synchronized to the Master. |
PASSIVE |
Port is aware of a better clock than the one it would advertise if it was in MASTER state and is not a Slave clock to that Master clock. |
PTP Support Information
This table lists different types of support information related to PTP:
Transport Media |
|
Messages |
|
Transport Modes |
|
PTP Hardware Support Matrix
Note |
The table also contains support details of upcoming releases. You can read this table in context of the current release and see relevant Release Notes for more information on supported features and hardware. |
This table provides a detailed information on the supported hardware:
Hardware Variant |
1588/PTP |
Cisco IOS XR |
Cisco IOS XR 64 bit |
Comments |
A9K-8X100GE-L-SE/TR (10GE and 100GE) |
Default & G.8265.1 |
5.3.3 |
6.3.2 6.4.1 |
PTP over Ethernet does not work on 100G ports on Cisco IOS XR until 6.4.1. Support was introduced in 6.4.1. |
G.8275.1 & G.8275.2 |
6.2.1 |
6.3.2 6.4.1 |
||
G.8273.2 |
6.2.1 |
6.3.2 |
||
PTP Multiprofile |
6.5.1 |
6.5.1 |
||
A9K-RSP880-SE/TR |
1588/PTP Default & G.8265.1 |
5.3.3 |
6.3.2 6.4.1 |
- |
1588/PTP G.8275.1 & G.8275.2 |
6.2.1 |
6.3.2 6.4.1 |
||
1588/PTP G.8273.2 |
6.2.1 |
6.3.2 6.4.1 |
||
PTP Multiprofile |
6.5.1 |
6.5.1 |
||
A9K-8X100GE-L-SE/TR (40-GE) |
1588/PTP Default & G.8265.1 |
6.0.1 |
6.3.2 6.4.1 |
- |
1588/PTP G.8275.1 & G.8275.2 |
6.2.1 |
6.3.2 6.4.1 |
||
1588/PTP G.8273.2 |
NA |
NA |
||
PTP Multiprofile |
6.5.1 |
6.5.1 |
||
A9K-4X100GE-SE/TR A9K-8X100GE-SE/TR |
1588/PTP Default & G.8265.1 |
6.2.1 |
6.4.1 |
PTP over Ethernet does not work on 100G ports on Cisco IOS XR until 6.4.1. Support was introduced in 6.4.1. In 6.2.1, only G.8275.1 PTP profile is supported on the cards; No support for G.8273.2 PTP profile. |
1588/PTP G.8275.1 & G.8275.2 |
6.2.1 |
6.4.1 |
||
1588/PTP G.8273.2 |
6.4.1 |
6.4.1 |
||
PTP Multiprofile |
6.5.1 |
6.5.1 |
||
A9K-MOD400-SE/TR & A9K-MOD200-SE/TR with Legacy MPAs |
1588/PTP Default & G.8265.1 |
6.1.3 |
6.4.1 |
- |
1588/PTP G.8275.1 & G.8275.2 |
6.2.2 |
6.4.1 |
- |
|
1588/PTP G.8273.2 |
- |
- |
- |
|
PTP Multiprofile |
6.5.1 |
6.5.1 |
- |
|
A9K-MOD400-SE/TR & A9K-MOD200-SE/TR with MPA 20x10GE , A9K-MPA-1X100GE and A9K-MPA-2X100GE |
1588/PTP Default & G.8265.1 |
6.1.3 |
6.4.1 |
PTP over Ethernet does not work on 100G ports on Cisco IOS XR until 6.4.1. Support was introduced in 6.4.1. In 6.2.2, only G.8275.1 PTP profile is supported on the cards. No support for G.8273.2 PTP profile until 6.5.1. |
1588/PTP G.8275.1 & G.8275.2 |
6.2.2 |
6.4.1 |
||
1588/PTP G.8273.2 |
6.5.1 |
6.5.1 |
||
PTP Multiprofile |
6.5.1 |
6.5.1 |
||
A99-12X100GE |
1588/PTP Default & G.8265.1 |
6.3.2 |
6.3.2 |
- |
1588/PTP G.8275.1 & G.8275.2 |
6.3.2 |
6.3.2 |
||
1588/PTP G.8273.2 |
NA |
- |
||
PTP Multiprofile |
6.5.1 |
6.5.1 |
||
A9K-24X10GE-1G-SE/TR A9K-48X10GE-1G-SE/TR |
1588/PTP Default & G.8265.1 |
6.2.2 6.3.1 |
6.3.2 |
- |
1588/PTP G.8275.1 & G.8275.2 |
6.2.2 6.3.1 |
6.3.2 |
||
1588/PTP G.8273.2 |
6.3.1 |
6.3.2 |
||
PTP Multiprofile |
6.5.1 |
6.5.1 |
||
A99-RSP-SE/TR (Cisco ASR 9910 Series Routers) |
1588/PTP Default & G.8265.1 |
6.3.1 |
6.3.2 |
- |
1588/PTP G.8275.1 & G.8275.2 |
6.3.1 |
6.3.2 |
||
1588/PTP G.8273.2 |
6.4.1 |
6.3.2 |
||
PTP Multiprofile |
6.5.1 |
6.5.1 |
||
A9K-RSP880-LT-SE/TR |
1588/PTP Default & G.8265.1 |
6.2.2 |
6.4.1 |
- |
1588/PTP G.8275.1 & G.8275.2 |
6.2.2 |
6.4.1 |
||
1588/PTP G.8273.2 |
6.4.1 |
6.4.1 |
||
PTP Multiprofile |
6.5.1 |
6.5.1 |
||
A9K-RSP440-TR/SE A99-RP-SE Enhanced Ethernet Linecards |
1588/PTP Default & G.8265.1 |
4.3.4 |
NA |
Enhanced Ethernet linecards do not support G.8273.2 with G.8275.1 PTP profile. . |
1588/PTP G.8275.1 & G.8275.2 |
NA |
NA |
||
1588/PTP G.8273.2 |
NA |
NA |
||
A99-RP2-TR/SE |
1588/PTP Default & G.8265.1 |
5.3.3 |
6.3.2 6.4.1 |
- |
1588/PTP G.8275.1 & G.8275.2 |
6.2.1 |
6.3.2 6.4.1 |
||
1588/PTP G.8273.2 |
NA |
NA |
||
Cisco ASR 9001 Series Routers |
1588/PTP Default & G.8265.1 |
4.3.4 |
NA |
Enhanced Ethernet based hardware does not support G.8273.2 with G.8275.1 PTP profile. |
1588/PTP G.8275.1 & G.8275.2 |
NA |
NA |
||
1588/PTP G.8273.2 |
NA |
NA |
||
Cisco ASR 9901 Series Routers |
1588/PTP Default & G.8265.1 |
NA |
6.4.1 |
- |
1588/PTP G.8275.1 & G.8275.2 |
NA |
6.4.1 |
||
1588/PTP G.8273.2 |
NA |
6.6.1 |
||
PTP Multiprofile |
NA |
6.5.1 |
||
A99-RSP-SE/TR (Cisco ASR 9906 Series Routers) |
1588/PTP Default & G.8265.1 |
6.3.1 |
6.3.2 |
- |
1588/PTP G.8275.1 & G.8275.2 |
6.3.1 |
6.3.2 |
||
1588/PTP G.8273.2 |
6.4.1 |
6.3.2 |
||
PTP Multiprofile |
6.5.1 |
6.5.1 |
||
A9K-RSP5-SE |
1588/PTP Default & G.8265.1 |
NA |
6.5.15 |
- |
1588/PTP G.8275.2 |
NA |
6.5.15 |
||
1588/PTP G.8275.1 & G.8273.2 |
NA |
6.6.1 |
||
PTP Multiprofile |
NA |
6.5.15 |
||
A9K-RSP5-TR |
1588/PTP Default & G.8265.1 |
NA |
6.5.15 |
- |
1588/PTP G.8275.2 |
NA |
6.5.15 |
||
1588/PTP G.8275.1 & G.8273.2 |
NA |
6.6.1 |
||
PTP Multiprofile |
NA |
6.5.15 |
||
A99-RP3-SE |
1588/PTP Default & G.8265.1 |
NA |
6.5.15 |
- |
1588/PTP G.8275.2 |
NA |
6.5.15 |
||
1588/PTP G.8275.1 & G.8273.2 |
NA |
6.6.1 |
||
PTP Multiprofile |
NA |
6.5.15 |
||
A99-RP3-TR |
1588/PTP Default & G.8265.1 |
NA |
6.5.15 |
- |
1588/PTP G.8275.2 |
NA |
6.5.15 |
||
1588/PTP G.8275.1 & G.8273.2 |
NA |
6.6.1 |
||
PTP Multiprofile |
NA |
6.5.15 |
||
A9K-8X100GE-X-TR |
1588/PTP Default & G.8265.1 |
NA |
6.5.15 |
- |
1588/PTP G.8275.2 |
NA |
6.5.15 |
||
1588/PTP G.8275.1 & G.8273.2 |
NA |
6.6.1 |
||
PTP Multiprofile |
NA |
6.5.15 |
||
A9K-16X100GE-TR |
1588/PTP Default & G.8265.1 |
NA |
6.5.15 |
NA |
1588/PTP G.8275.2 |
NA |
6.5.15 |
||
1588/PTP G.8275.1 & G.8273.2 |
NA |
6.6.1 |
||
PTP Multiprofile |
NA |
6.5.15 |
||
A9K-32X100GE-TR |
1588/PTP Default & G.8265.1 |
NA |
6.5.15 |
- |
1588/PTP G.8275.2 |
NA |
6.5.15 |
||
1588/PTP G.8275.1 & G.8273.2 |
NA |
6.6.1 |
||
PTP Multiprofile |
NA |
6.5.15 |
Restrictions
-
PTP Grandmaster (GM) is not supported with all the PTP profiles.
-
RSP IEEE 1588 port on RSP/RP is not supported.
-
Two-step clock operation is recommended over one-step clock operation for a PTP Master.
-
1 Pulse per Second (1PPS) output is not supported on Cisco ASR 9000 Series Routers.