The following PTP restrictions apply to the Cisco NCS 5500 Series Router:

• NCS55-RP does not support PTP

• NC55-18H18F line card does not support PTP

• SyncE is not supported on a 1GE copper SFP.

• SyncE is not supported on 25 GE or 100 GE interfaces when they are used in 1G mode.

• Sync2 interface is supported only if 10 MHz, 1 Pulse per Second (PPS) and time-of-day (ToD) ports are configured.

• PTP is not supported with MACSec.

• G.8273.2 Class-A performance is met if CFP2-DCO is configured on either Slave or Master port on the node.

• Transparent Clock is not supported.

• PTP over MPLS is not supported.

Note	We recommend you to configure, and enable Frequency Synchronization selection input on two interfaces per line card. For link aggregation, you must configure and enable Frequency Synchronization selection input on a single bundle member.

Under normal configured conditions, any change in offset triggers an immediate reaction in the servo. With the Slow Tracking feature enabled, the servo corrects the phase offset based on the configured value. If the phase offset exceeds the acceptable range, servo goes into Holdover state. In such a condition, the Slow Tracking feature becomes inactive and the servo corrects itself to the latest offset and goes into Phase locked state. Slow Tracking becomes active again.

Note	The supported slow tracking rate range is from 8-894 nanoseconds per second and must be in multiples of 8. This feature is active only when servo is in Phase locked mode.

Router:# config
ptp
clock
domain 24
profile g.8275.1 clock-type T-BC
!
profile profile1
multicast target-address ethernet 01-1B-19-00-00-00
transport ethernet
sync frequency 16
clock operation one-step
announce frequency 8
delay-request frequency 16
!
physical-layer-frequency
servo-slow-tracking 16
!

G.8265.1 profile fulfills specific frequency-distribution requirements in telecom networks. Features of G.8265.1 profile are:

• Clock advertisement: G.8265.1 profile specifies changes to values used in Announce messages for advertising PTP clocks. The clock class value is used to advertise the quality level of the clock, while the other values are not used.

• Clock Selection: G.8265.1 profile also defines an alternate Best Master Clock Algorithm (BMCA) to select port states and clocks is defined for the profile. This profile also requires to receive Sync messages (and optionally, Delay-Response messages) to qualify a clock for selection.

• Port State Decision: The ports are statically configured to be Master or Slave instead of using state machines to dynamically set port states.

• Packet Rates: The packet rates higher than rates specified in the IEEE 1588-2008 standard are used. They are:

  • Sync/Follow-Up Packets: Rates from 128 packets-per-second to 16 seconds-per-packet.

  • Delay-Request/Delay-Response Packets: Rates from 128 packets-per-second to 16 seconds-per-packet.

  • Announce Packets: Rates from 8 packets-per-second to 64 packets-per-second.

• Transport Mechanism: G.8265.1 profile only supports IPv4 PTP transport mechanism.

• Mode: G.8265.1 profile supports transport of data packets only in unicast mode.

• Clock Type: G.8265.1 profile only supports Ordinary Clock-type (a clock with only one PTP port).

• Domain Numbers: The domain numbers that can be used in a G.8265.1 profile network ranges from 4 to 23. The default domain number is 4.

• Port Numbers: All PTP port numbers can only be one (1) because all clocks in this profile network are Ordinary Clocks.

G.8265.1 profile defines an alternate algorithm to select between different master clocks based on the local priority given to each master clock and their quality levels (QL). This profile also defines Packet Timing Signal Fail (PTSF) conditions to identify the master clocks that do not qualify for selection. They are:

• PTSF-lossSync condition: Raised for master clocks that do not receive a reliable stream of Sync and Delay-Resp messages. Cisco IOS XR software requests Sync and Delay-Resp grants for each configured master clock to track the master clock with this condition.

• PTSF-lossAnnounce condition: Raised for master clocks that do not receive a reliable stream of Announce messages.

• PTSF-unusable condition: Raised for master clocks that receives a reliable stream of Announce, Sync, and Delay-Resp messages, but not usable by slave clocks. Cisco IOS XR software does not use this condition.

G.8275.1 profile fulfills the time-of-day and phase synchronization requirements in telecom networks with all network devices participating in the PTP protocol. G.8275.1 profile provides better frequency stability for the time-of-day and phase synchronization.

Features of G.8275.1 profile are:

• Synchronization Model: G.8275.1 profile adopts hop-by-hop synchronization model. Each network device in the path from master to slave synchronizes its local clock to upstream devices and provides synchronization to downstream devices.

• Clock Selection: G.8275.1 profile also defines an alternate BMCA that selects a clock for synchronization and port state for the local ports of all devices in the network is defined for the profile. The parameters defined as a part of the BMCA are:

  • Clock Class

  • Clock Accuracy

  • Offset Scaled Log Variance

  • Priority 2

  • Clock Identity

  • Steps Removed

  • Port Identity

  • notSlave flag

  • Local Priority

• Port State Decision: The port states are selected based on the alternate BMCA algorithm. A port is configured to a master-only port state to enforce the port to be a master for multicast transport mode.

• Packet Rates: The nominal packet rate for Announce packets is 8 packets-per-second and 16 packets-per-second for Sync/Follow-Up and Delay-Request/Delay-Response packets.

• Transport Mechanism: G.8275.1 profile only supports Ethernet PTP transport mechanism.

• Mode: G.8275.1 profile supports transport of data packets only in multicast mode. The forwarding is done based on forwardable or non-forwardable multicast MAC address.

• Clock Type: G.8275.1 profile supports the following clock types:

  • Telecom Grandmaster (T-GM): Provides timing for other network devices and does not synchronize its local clock to other network devices.

  • Telecom Time Slave Clock (T-TSC): A slave clock synchronizes its local clock to another PTP clock, but does not provide PTP synchronization to any other network devices.

  • Telecom Boundary Clock (T-BC): Synchronizes its local clock to a T-GM or an upstream T-BC clock and provides timing information to downstream T-BC or T-TSC clocks.

• Domain Numbers: The domain numbers that can be used in a G.8275.1 profile network ranges from 24 to 43. The default domain number is 24.

The G.8275.1 supports the following:

• T-GM: The telecom grandmaster (T-GM) provides timing to all other devices on the network. It does not synchronize its local clock with any other network element other than the Primary Reference Time Clock (PRTC).

• T-BC: The telecom boundary clock (T-BC) synchronizes its local clock to a T-GM or an upstream T-BC, and provides timing information to downstream T-BCs or T-TSCs. If at a given point in time there are no higher-quality clocks available to a T-BC to synchronize to, it may act as a grandmaster.

• T-TSC: The telecom time slave clock (T-TSC) synchronizes its local clock to another PTP clock (in most cases, the T-BC), and does not provide synchronization through PTP to any other device.

The following figure describes a sample G.8275.1 topology.

Route Processor Fail Over

The Route processor fail over (RPFO) or stateful switchover (SSO) feature is supported on the Profile G.8275.1 on the Telecom Boundary Clock. Over a switchover, the time error might jump to a high value after losing lock with the T-GM clock. With this feature enabled, the time error will not increase by more than 400 nanoseconds over a switchover.

Note	You must wait for a specific time duration to lapse to build holdover.

The G.8275.2 is a PTP profile for use in telecom networks where phase or time-of-day synchronization is required. It differs from G.8275.1 in that it is not required that each device in the network participates in the PTP protocol. Also, G.8275.2 uses PTP over IPv4 in unicast mode.

Effective Cisco IOS XR Software Release 7.8.1, the G.8275.2 is capable of using PTP over IPv6 as well. You can now use the transport ipv6 command to set this encapsulation type.

The G.8275.2 profile is based on the partial timing support from the network. Hence nodes using G.8275.2 are not required to be directly connected.

The G.8275.2 profile is used in mobile cellular systems that require accurate synchronization of time and phase. For example, the fifth generation (5G) of mobile telecommunications technology.

Note

G.8275.2 profile is supported on Cisco NCS 5500 Series Routers. However, the performance standards of this profile is not aligned with any of the ITU-T standards because performance specifications for G.8275.2 profile has not yet been made available by ITU-T. For more information on hardware that supports G.8275.2 profile configurations, refer to Supported Hardware section in this chapter.

Features of G.8275.2 profile are:

• Clock Selection: G.8275.2 profile also defines an alternate BMCA that selects a clock for synchronization and port state for the local ports of all devices in the network is defined for the profile. The parameters defined as a part of the BMCA are:

  • Clock Class

  • Clock Accuracy

  • Offset Scaled Log Variance

  • Priority 2

  • Clock Identity

  • Steps Removed

  • Port Identity

  • notSlave flag

  • Local Priority

  Note	See ITU-T G.8275.2 document to determine the valid values for Clock Class parameter.

• Port State Decision: The port states are selected based on the alternate BMCA algorithm. A port is configured to a master-only port state to enforce the port to be a master for unicast transport mode.

• Packet Rates:

  • Synchronization/Follow-Up—minimum is one packet-per-second and maximum of 128 packets-per-second.

  • Packet rate for Announce packets—minimum of one packet-per-second and maximum of eight packets-per-second.

  • Delay-Request/Delay-Response packets—minimum is one packet-per-second and maximum of 128 packets-per-second

• Transport Mechanism: G.8275.2 profile supports only IPv4 PTP transport mechanism.

• Mode: G.8275.2 profile supports transport of data packets only in unicast mode.

• Clock Type: G.8275.2 profile supports the following clock types:

  • Telecom Grandmaster (T-GM): Provides timing for other network devices and does not synchronize its local clock to other network devices.

  • Telecom Time Slave Clock (T-TSC): A slave clock synchronizes its local clock to another PTP clock, but does not provide PTP synchronization to any other network devices.

  • Telecom Boundary Clock (T-BC): Synchronizes its local clock to a T-GM or an upstream T-BC clock and provides timing information to downstream T-BC or T-TSC clocks.

• Domain Numbers: The domain numbers that can be used in a G.8275.2 profile network ranges from 44 to 63. The default domain number is 44.

Starting from Release 7.2.1, PTP Multi-profile is supported for the below combination of PTP profiles:

• G8275.1

• G8275.2

With an increase in diversification in deployment of backhaul networks, there is a need to have the ability to select and advertise the best clock source between a PTP server and other local timing sources connected to the device. ITU-T G.8275 specifies associating a virtual PTP port to an external clock input of the device. This allows the external clock inputs to participate in PTP protocol to select the best clock source between a PTP server and other local timing sources connected to the device.

G.8275.1 introduces the concept of a virtual port on the T-BC. A virtual port is an external frequency, phase,and time input interface on a T-BC, which can participate in the source selection.

The Assisted Partial Timing Support (APTS) enables you to deliver accurate timing and synchronization in mobile backhaul networks. ITU-T G.8275 specifies the APTS architectures where PTP is used as a backup timing source to a local time reference. The local time reference is generally a GNSS-based PRTC clock.