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Hybrid Mode

Hybrid Mode Overview

The combined operation of Synchronous Ethernet and Precision Time Protocol (PTP) is also known as hybrid mode.

In hybrid mode, the synchronous Ethernet equipment clock (EEC) on the Modular Port Concentrator (MPC) derives the frequency from Synchronous Ethernet and the phase and time of day from PTP. Time synchronization includes both phase synchronization and frequency synchronization.

Synchronous Ethernet is a physical layer–based technology that functions regardless of the network load. Synchronous Ethernet supports hop-by-hop frequency transfer, where all interfaces on the trail must support Synchronous Ethernet. PTP (also known as IEEE 1588v2) synchronizes clocks between nodes in a network, thereby enabling the distribution of an accurate clock over a packet-switched network. This synchronization is achieved through packets that are transmitted and received in a session between a primary clock (commonly called the primary) and a client clock (also known as the client in PTP terminology).


Router clocks are categorized based on the role of the router in the network. Router clocks are broadly categorized into ordinary clocks and boundary clocks. The primary clock and the client clock are known as ordinary clocks. The boundary clock can operate as either a primary or a client.

Synchronous Ethernet works on the principle of frequency synchronization, whereby the frequencies of all the clocks (intermediate primary and client clocks) in the network are synchronized to the frequency of the primary clock at the starting end of the network trail. PTP works on the principle of phase synchronization and frequency synchronization—it synchronizes both frequency and phase, including time of day. Phase synchronization is achieved either by adjusting the phase of the client clock (the router’s internal clock oscillator) discontinuously by receiving clock signals from the primary clock at irregular periods of time or by adjusting the phase-locked loop of the client internal clock at regular intervals. The accuracy of clock synchronization depends on factors such as packet delay variation, quality of oscillator used, network asymmetry, and so on.

Synchronous Ethernet and PTP provide frequency and phase synchronization; however, accuracy in the order of nanoseconds is difficult to achieve through PTP or Synchronous Ethernet and these technologies do not support a large number of network hops. Hybrid mode resolves these issues by extending the number of network hops and also provides clock synchronization accuracy in the order of tens of nanoseconds. Hybrid mode is configured on the client. On the client, you can configure one or more interfaces as Synchronous Ethernet source interfaces.

Hybrid mode has an internal threshold value of 100 nanoseconds for the PTP phase difference before the PTP phase adjustment can initiate. To understand PTP phase difference and adjustment, consider a scenario involving two PTP sources—PTP1 and PTP2—and one Synchronous Ethernet source. Assume that initially the PTP1 source and the Synchronous Ethernet source are up and the PTP2 source is down. Also, assume that the router clock (client) is synchronized to the available PTP source—PTP1—and the Synchronous Ethernet source. Suppose that after sometime the PTP1 source goes down because of technical issues—during which time the PTP2 source has come up—which, in turn, triggers the best primary clock algorithm to run automatically, latching the router clock to the next available PTP source—that is, the PTP2 source—and the Synchronous Ethernet source. Note that a PTP phase adjustment is triggered when the phase difference between the current actual time of day (TOD) and the TOD as calculated by the algorithm as a result of the communication with the PTP2 source is at least 100 nanoseconds. Although this phase difference can occur anytime during the operation of the router in hybrid mode, this phase difference is more likely to occur only during PTP source switchover. You must always add a measurement error of 10 through 20 nanoseconds to the original internal threshold value. This error adjustment results in a phase difference threshold value of 110–120 nanoseconds.

In hybrid mode, the following show commands display information regarding the hybrid status configuration:

  • The show ptp status details command displays the time and phase plane status.

  • The show chassis synchronization extensive command displays the frequency plane status.

  • The show ptp hybrid status command displays the hybrid (combined status of frequency and phase plane) status.

  • In hybrid mode, the show ptp hybrid status and show ptp lock-status commands indicate the lock status as Phase Aligned in the output.

You can use the show ptp hybrid status operational command to find the current operating mode.


In hybrid mode, the EEC in the MPC derives frequency synchronization from Synchronous Ethernet and the phase and time of day from PTP. However, the show chassis synchronization extensive operational mode command output displays the lock status that is derived from the EEC located on the SCB.

Hybrid Mode Support on Junos OS Devices

Hybrid mode is supported on the Juniper Networks MX104, MX240, MX480, and MX960 Universal Routing Platforms and on the Juniper Networks MX80 Universal Routing Platforms with precision timing support (MX80-P) and with timing support (MX80-T).

The 10GE, 40G, and 100GE WAN ports on MX10003 and MX204 routers support the hybrid mode feature.

On the MX240, MX480, MX960, MX2008, MX2010, and MX2020 routers, the combined operation is possible only when the PTP client and the Synchronous Ethernet source are on the same enhanced MPC and are traceable to the same primary reference clock (PRC). On MX10003, the Synchronous Ethernet source can be from any MPC for the combined operation.

Junos OS supports hybrid mode over link aggregation group (LAG) for MPC2E NG, MPC3E NG, MPC5E, MPC6E, MPC7E-10G, MPC7E–MRATE, MPC8E, MPC9E, and MPC10E line cards. The hybrid operation over LAG is supported only when primary and secondary Synchronous Ethernet interfaces are present on the same line card. The MPC2E NG, MPC3E NG, MPC5E, MPC6E, MPC7E-10G, MPC7E–MRATE, MPC8E, and MPC9E line cards support both PTP over IPv4 and PTP over Ethernet in hybrid mode over LAG. The MPC10E line cards support PTP over Ethernet in hybrid mode over LAG.

This table summarizes the first Junos OS release that supports hybrid mode over LAG on various Juniper Networks devices:

Table 1: Hybrid mode over LAG Support

Juniper Network Devices

PTP over IPv4 in hybrid mode over LAG

PTP over Ethernet in hybrid mode over LAG



























When acting as PTP slaves, MX80-P routers can accept any external Synchronous Ethernet clock as reference and do not support building-integrated timing supply (BITS) input as frequency source in hybrid mode of operation. Only Synchronous Ethernet sources are allowed in hybrid mode. Note that when the selected Synchronous Ethernet reference fails, the router continues to work in PTP mode.

Unified in-service software upgrade (unified ISSU) is not supported when clock synchronization is configured for hybrid mode on MX80-P, MX80-T, MX10003, MX2008, MX2010, MX2020 routers, and on the MICs and enhanced MPCs on MX240, MX480, and MX960 routers.


To switch between PTP and Synchronous Ethernet modes, you must first deactivate the configuration for the current mode and then commit the configuration. Wait for 30 seconds and then configure the new mode and its related parameters, and then commit the configuration.

Guidelines to Configure Hybrid Mode

Keep the following points in mind while configuring hybrid mode on ACX Series routers:

  • In a Hybrid Operation, the Frequency module derives frequency from the Synchronous Ethernet or BITS (T1/E1) clock or 10 MHz clock and Phase from the IEEE-1588v2 (PTPv2). The current deployments are all LTE-TDD based and require a phase accuracy of only 1.5us and it is expected that this performance can be achieved without requiring frequency assist.

  • Frequency Plane (Synchronous Ethernet, BITS (T1/E1), 10 MHz) is not impacted by the phase or time plane. The frequency plane derives the frequency from Synchronous Ethernet, BITS (T1/E1) and 10 MHz.

  • Phase/Time Plane uses the Frequency which is derived locally from the equipment (Synchronous Ethernet, BITS (T1/E1), 10 MHz). To achieve phase accuracy of less than 1.5us, both Frequency Input source and PTP sources traceable to a primary reference source (PRS) or primary reference clock (PRC). Hybrid mode is supported in a ring topology.

  • You can configure the following frequency sources for hybrid node:

    • Synchronous Ethernet 1G, 10G with/without ESMC

    • BITS T1 Clock

    • BITS E1 Clock

    • 10 MHz Clock

    • T1 Interface

    • E1 Interface

  • You can configure the following phase sources for hybrid node:

    • PTP IPv4 with or without unicast negotiation

    • PTPoE with or without stateful port

  • By enabling the hybrid mode, the convergence time period is reduced and locking happens quickly.

  • You can configure the PTP Source as phase or time source for hybrid mode.

  • You can configure Layer 2 rings for PTPoE with stateful ports and Synchronous Ethernet with ESMC for Layer 2 ring topologies.

  • When you enable hybrid mode, each node generates a phase error of or plus or minus 100 nanoseconds (without Phy Timestamping) or plus or minus 50 nanoseconds with Phy timestamping feature. This phenomenon requires Frequency (SyncE/BITS/10 MHz) source and PTP source must be traceable to same PRC/PRS source.

  • Fully redundant and resilient ring based configurations of up to 10 nodes are supported, targeting the 1 microsecond phase requirement for a form of 4G known as Long-Term Evolution-Time Division Duplex (LTE-TDD). A single node or link failure is accommodated and all nodes are able to maintain phase accuracy to be +/- 1us accurate to a common source.

  • Hybrid mode for PTP IPv4 rings is not supported.

  • Dynamic switchover from Hybrid to PTP mode is not supported in ACX routers.

  • BITS T1 Clock with SSM is not supported. BITS E1 Clock with SSM is not supported.

  • Hybrid Mode: Time Of Day (TOD) as Phase and Frequency as SyncE/BITS/10 MHz is not supported. Simultaneous PTP IPv4 Ring and SyncE Hybrid Mode are not supported.

  • Hybrid Mode with Phy Timestamping feature is not supported only on ACX500 series routers.

  • Dynamic Switchover from Hybrid to the PTP Mode feature is not supported.

  • The hybrid feature on aggregated Ethernet (ae-) interfaces is not supported.

  • When you configure hybrid mode, the following processes take place.

    • The best of the configured PTP time sources is selected by the PTP Best Primary Clock Algoritm (BMCA).

    • The best of configured chassis synchronization sources is selected by the synchronization source selection algorithm.

    • During the boot-up process, if valid sources are configured at the [edit chassis synchronization] hierarchy level and chassis synchronization mode in free-running mode, valid PTP source available case, system continues to operate in hybrid mode (In this case, chassis synchronization is in free-run mode, whereas PTP is in locked mode). When both primary and secondary frequency sources fail, system still works under hybrid mode (In this case, chassis synchronization is in hybrid mode and PTP is in locked mode).