Hybrid Mode

Hybrid Mode Overview

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).

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.

For information about configuring hybrid mode, see Configuring Hybrid Mode and ESMC Quality Level Mapping. You can use the show ptp hybrid status operational command to find the current operating mode.

Supporting Platforms

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).

Starting in Junos OS Release 17.4R1, 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:

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.