Understanding ESMC Quality Level Mapping

Synchronous Ethernet Mode

In Synchronous Ethernet mode, the ESMC quality level is handled in the following way:

• In quality mode:

  • If the quality-mode-enable option at the [show chassis synchronization] hierarchy level is not set, then the configured quality and the priority set for the clock sources are used for the clock selection. The ESMC quality level is based on the configured quality level corresponding to the active clock source.

  • If the quality-mode-enable option at the [show chassis synchronization] hierarchy level is set, then only those clock sources that receive ESMC quality level is higher than or equal to the configured quality are considered for selection. The ESMC quality level value transmitted also depends on the selection mode option as discussed next.

• In selection mode:

  • If the selection-mode option at the [show chassis synchronization] hierarchy level is set to configured-quality, then the configured quality for the selected, active source is used as the system ESMC quality level value that is transmitted out.

  • If the selection-mode option at the [show chassis synchronization] hierarchy level is set to received-quality, then the received ESMC quality level value from the selected clock source is transmitted out.

• When no clock sources are locked:

  1. Do Not Use (DNU)/Don’t Use for Synchronization (DUS) quality level is transmitted.

  2. The ESMC quality level value sent out on the selected, active clock source interface is always DNU/DUS.

Precision Time Protocol Mode

In Precision Time Protocol (PTP) mode, you can transmit ESMC quality level values with the following parameters set:

• The network-option option must be configured at the [edit chassis synchronization] hierarchy level.

• Synchronous Ethernet sources must not be configured at the [edit chassis synchronization] hierarchy level.

• The convert-clock-class-to-quality-level option at the [edit protocols ptp slave] hierarchy level must be enabled so that the PTP clock class received from the selected primary is converted to the appropriate ESMC quality level.

Clock class is a value that ranges from 80 through 109 and is used to map the clock class to the set ESMC quality level. The ESMC quality level value is mapped to the clock class value by one of the following methods:

• Mapping of PTP clock class to ESMC quality level—By default, the standard mappings suggested by ITU-T G.781 specification are used as shown in Table 1 and irrespective of the clock being configured in hybrid mode or pure PTP mode, the outgoing quality level is always based on the PTP clock class mapping. To map the PTP clock class to the ESMC quality level, you must set the convert-clock-class-to-quality-level option at the [edit protocols ptp slave] hierarchy level. For default mapping values, see Table 1.

  Table 1: Default Quality Level to PTP Clock-Class Mapping

  SSM QL (Binary)	Standard Mappings Given in ITU-T G.781 Specification		PTP Clock Class
  	Option I	Option II
  0001	-	QL-PRS	80
  0000	-	QL-STU	82
  0010	QL-PRC	-	84
  0111	-	QL-ST2	86
  0011	-	-	88
  0100	QL-SSU-A	QL-TNC	90
  0101	-	-	92
  0110	-	-	94
  1000	QL-SSU-B	-	96
  1001	-	-	98
  1101	-	QL-ST3E	100
  1010	-	QL-ST3/QL-EEC2	102
  1011	QL-SEC/QL-EEC1		104
  1100	-	QL-SMC	106
  1110	-	QL-PROV	108
  1111	QL-DNU	QL-DUS	110

• User-defined mapping of PTP clock class to ESMC quality level—You can manually override the clock class to ESMC mapping by setting the clock-class option at the [edit protocols ptp slave clock-class-to-quality-level-mapping quality level ql-value] hierarchy level.

Unlike Synchronous Ethernet, the DNU/DUS quality level value is not transmitted on the interface on which the PTP primary is configured. In PTP mode, an interface is configured as part of the [edit chassis esmc-transmit interfaces] hierarchy level, and an appropriate ESMC quality level value is transmitted through it. Note that when the PTP clock class value received from the primary changes, the ESMC quality level transmitted also changes appropriately. If there is no valid clock class value as input, then the DNU/DUS value is transmitted on the interfaces configured under the esmc-transmit option at the [edit chassis synchronization] hierarchy level.

To view the current mapping between the clock class and the ESMC quality level, run the show ptp quality-level-mapping operational mode command.

To display the ESMC quality level currently transmitted by the interface, run the show ptp global-information operational mode command in PTP or hybrid mode. Note that when the convert-clock-class-to-quality-level option is disabled or when there is no valid clock class as input, the show ptp global information command does not display the ESMC quality level value.

To view the ESMC quality level transmitted in all modes, run the show synchronous-ethernet esmc transmit detail operational mode command.

Hybrid Mode

Hybrid mode is a combination of PTP and Synchronous Ethernet modes.

The configuration required for transmitting the ESMC quality level in hybrid mode differs from that in PTP mode in the following ways:

• In hybrid mode, synchronous Ethernet source interfaces must be configured at the [edit chassis synchronization] hierarchy level.

• In hybrid mode, configuring the convert-clock-class-to-quality-level option is optional. When this option is configured, the outgoing ESMC quality level behavior is the same as that in PTP mode. When the convert-clock-class-to-quality-level option is not configured, the outgoing ESMC quality level behavior is the same as that in Synchronous Ethernet mode.

Feature Mode Changes

When the router configuration is changed from one feature mode to another mode—that is from or to Synchronous Ethernet, PTP, or hybrid mode—the following occurs:

1. The ESMC quality level is reset to DNU.

2. Based on the new feature mode, the ESMC quality level is decided:

   • When the reference clock qualifies for Synchronous Ethernet mode.

   • When PTP goes into phase-aligned state or hold-over state in PTP mode.

   • When the hybrid state reaches frequency and phase aligned state in hybrid mode.

Sometimes PTP is required to drive Synchronous Ethernet and ESMC. This scenario occurs when:

• After certain PTP hops, the network branches out, and one branch of the network requires only frequency synchronization while the other branch requires both phase and frequency synchronization.

• A packet-based distribution network is located between a time-division multiplexing (TDM), a SONET, and a Synchronous Ethernet network.

In such situations, the clock recovered by PTP is sent over the Ethernet physical transceiver for Synchronous Ethernet, and the ESMC quality level value mapping with the PTP clock class is sent over the interfaces.