PTP over IRB for G.8275.2 Enhanced Profile
PTP over IRB for G.8275.2 enhanced profile enables precise timing synchronization in Remote PHY deployments by allowing PTP timeTransmitter configuration on IRB interfaces. This feature supports clustered RPD environments with a single PTP timeTransmitter serving multiple timeReceivers, AE integration within bridge domains, and redundancy through primary/secondary link configuration. It ensures telecom-grade synchronization for DOCSIS and emerging services like wireless backhaul.
Overview
Timing and synchronization are essential for Data-over-Cable Service Interface Specification (DOCSIS) based cable deployments and advanced services such as wireless backhaul. In Remote PHY architectures, subscribers connect through DOCSIS cable modems to Remote PHY Devices (RPD) via coaxial cables, which aggregate at the Converged Cable Access Platform (CCAP) connected to the core network. While downstream and upstream PHY timing remain aligned because they are co-located, DOCSIS upstream scheduling requires accurate timestamp exchange between the CCAP core and RPD. To achieve this, Remote Dynamic Threat Intelligence (R-DTI) leverages IEEE 1588v2 Precision Time Protocol (PTP), supporting both basic synchronization for DOCSIS/video/OOB services and precision timing for advanced applications.
PTP Deployment
For deployments using the G.8275.2 enhanced PTP profile, multiple RPDs are grouped in clusters requiring synchronization from a single PTP timeTransmitter to multiple timeReceivers. This is implemented using Integrated Routing and Bridging (IRB), which enables Layer 2 bridging and Layer 3 routing on the same interface. The PTP timeTransmitter uses an IRB IP address, while each timeReceiver operates with an individual IP. This design allows a single local IP on the timeTransmitter to serve multiple nodes efficiently.
When configuring the PTP timeTransmitter on an IRB interface, the user must also specify the Layer 2 IFL (l2_ifl) name along with the clock client configuration. This ensures that PTP timeTransmitter streams are created only on the line card corresponding to the specified l2_ifl, avoiding redundant stream creation on unrelated line cards. The datapath for PTP packets remains consistent with the standard IPv4/IPv6 mode of operation.
AE Support over IRB
The feature also supports Aggregated Ethernet (AE) configuration within the bridge domain associated with an IRB. AE groups can span child interfaces across multiple line cards. To manage configuration complexity, PTP support will be restricted to two child interfaces per AE bundle. This provides flexibility while maintaining operational simplicity.
Active/Secondary Link Configuration
For PTP streams configured over an AE bundle, users can designate primary and secondary member links for redundancy. Each AE IFL configured as a PTP timeTransmitter must have one member link set as primary and another as secondary. To achieve both link-level and FPC-level redundancy, it is recommended that primary and secondary links reside on separate line cards. If both links are on the same line card, redundancy will be limited to link-level only.
Benefits
- Enables scalable and precise timing synchronization for clustered RPD deployments.
- Meets stringent requirements of the G.8275.2 enhanced profile for telecom-grade synchronization.
- Provides flexibility with IRB and AE configurations across multiple line cards.
- Supports redundancy for high availability in critical deployments.
CLI Configuration
A sample configuration to enable PTP over IRB for G 8275.1 enhanced profiles is given below:
set protocols ptp clock-mode boundary set protocols ptp profile-type g.8275.2.enh set protocols ptp domain 44 set protocols ptp unicast-negotiation set protocols ptp phy-timestamping set protocols ptp slave interface xe-0/1/14.0 unicast-mode transport ipv4 set protocols ptp slave interface xe-0/1/14.0 unicast-mode clock-source 50.0.0.1 local-ip-address 50.0.0.2 set protocols ptp master interface irb.8 unicast-mode transport ipv4 set protocols ptp master interface irb.10 unicast-mode transport ipv4 set protocols ptp master interface irb.10 unicast-mode clock-client 70.0.0.1/32 local-ip-address 70.0.0.2 l2-ifl xe-0/1/16.0 set bridge-domains bd3 vlan-id none set bridge-domains bd3 interface xe-0/1/16.0 set bridge-domains bd3 routing-interface irb.10
A sample configuration to enable PTP over IRB for G 8275.1 enhanced profiles with AE enabled is given below:
set chassis aggregated-devices ethernet device-count 10 set interfaces ge-4/1/1 gigether-options 802.3ad ae0 set interfaces ge-4/1/2 gigether-options 802.3ad ae0 set interfaces ge-4/1/0 unit 0 family inet address 50.0.0.2/24 set interfaces ae0 encapsulation ethernet-bridge set interfaces ae0 unit 0 set interfaces irb unit 0 family inet address 90.0.0.2/24 set protocols ptp clock-mode boundary set protocols ptp profile-type g.8275.2.enh set protocols ptp phy-timestamping set protocols ptp unicast-negotiation set protocols ptp slave delay-request -7 set protocols ptp slave interface ge-4/1/0.0 unicast-mode transport ipv4 set protocols ptp slave interface ge-4/1/0.0 unicast-mode clock-source 50.0.0.1 local-ip-address 50.0.0.2 set protocols ptp master interface irb.0 unicast-mode transport ipv4 set protocols ptp master interface irb.0 unicast-mode clock-client 90.0.0.1/32 local-ip-address 90.0.0.2 l2-ifl ae0 primary ge-4/1/1 set protocols ptp master interface irb.0 unicast-mode clock-client 90.0.0.1/32 local-ip-address 90.0.0.2 l2-ifl ae0 primary ge-4/1/2 set protocols ptp frequency-lock-threshold 15 set bridge-domains bd1 vlan-id none set bridge-domains bd1 interface ae0.0 set bridge-domains bd1 routing-interface irb.0
Monitoring and Verifying
Use the following CLI commands to monitor and verify the PTP over IRB setup.
show ptp lock-status detail
regress@integer> show ptp lock-status detail Lock Status: Lock State : 5 (PHASE ALIGNED) Phase offset : 0.000000003 sec State since : 2025-12-02 02:26:48 PST (2d 19:09 ago) Selected Master Details: Upstream Master address : 50.0.0.1 Slave interface : xe-0/1/14.0 Clock reference state : Clock locked 1pps reference state : Clock qualified
show ptp timeTransmitter detail
root@integer> show ptp master detail
PTP Master Interface Details:
Interface : irb.0
Status : Master, Active
Clock Info :
Local Address: 90.0.0.2 Status: Configured, Master, Active
Remote Address: 90.0.0.1 (ge-4/1/1.0) Status: SECURE AUTO SLAVE, Sig State: Ann + Sync
Total Remote Slaves: 1
show ptp timeReceiver detail
root@integer> show ptp slave detail
PTP Slave Interface Details:
Interface : ge-4/1/0.0
Status : Slave, Active
Clock Info
Local Address : 50.0.0.2 Status: Configured, Slave, Active
Remote Master: 50.0.0.1 Status: Configured, Master, Active
Total Remote Masters: 1
show ptp statistics detail
root@integer> show ptp statistics detail
Local Clock Remote Clock Role Stream Received Transmitted
ge-4/1/0.0 50.0.0.1 Slave 0 56436 28028
Signalling Announce Sync Delay Error
Rx: 6 442 27972 28022 0
Tx: 6 0 0 28024 0
Local Clock Remote Clock Role Stream Received Transmitted
irb.0 90.0.0.1 Master 4 28010 59619
ge-4/1/1.0
Signalling Announce Sync Delay Error
Rx: 9 0 0 28001 0
Tx: 9 3506 28103 28001 0
show ptp port detail
root@integer> show ptp port detail PTP port-data: Local Interface : ge-4/1/0.0 Local Address : 50.0.0.2 Remote Address : 50.0.0.1 Clock Stream : 0 Clock Identity : d4:04:ff:ff:fe:7e:5d:a2 Port State : Slave Delay Req Interval: -6 Announce Interval : 0 Announce Timeout : 3 Sync Interval : -6 Delay Mechanism : End-to-end Port Number : 2 Operating Mode : BMC Mode Local Priority : 128 Foreign Master Clock Details: Master Clock Id : 00:00:00:00:00:00:00:01 Previous Announce Messages : 0 Current Announce Messages : 0 Local Interface : irb.0 Local Address : 90.0.0.2 Remote Address : 90.0.0.1 Clock Stream : 4 Clock Identity : d4:04:ff:ff:fe:7e:5d:a2 Port State : Master Delay Req Interval: -6 Announce Interval : -3 Announce Timeout : 3 Sync Interval : -6 Delay Mechanism : End-to-end Port Number : 1 Operating Mode : Master Only Local Priority : 128
show ptp aggregated-ethernet-interfaces detail
root@integer# run show ptp aggregated-ethernet-interfaces detail Aggregated Interfaces status LAG-Mode : Revertive LAG-Link-BIND : FALSE AE: ae0.0 State: Up Role: Slave Primary: ge-4/0/0(active) Secondary: ge-4/0/1(secondary)