1000BaseT Ethernet interfaces

[niloda]

1000BaseT electrical Ethernet interfaces implicitly create a clock loop. In accordance with the IEEE 802.3-2018 standard (§1.4.456 slave Physical Layer (PHY)), when they are configured as slaves (see rx-sync-preference of wire-interface-configuration), the transmission clock is equal to the reception clock. This feature could create problems in a ring controlled by the SSM protocol.

As shown in the following figure, the clock runs counterclockwise giving LAN-1 a higher priority than LAN-2.

In case of failure between Ne-2 and Ne-3, Ne-3 is synchronized by changing the clock direction between Ne-1, Ne-2 and Ne-3. The role of the LAN-2 port of Ne-2 and Ne-3 must be forced to slave so that the clock direction can be reversed.

Of course, for the clock direction to be consistent in the ring, the master/slave roles of the 1000BaseT Ethernet interfaces should be driven by the SSM protocol. For this purpose, some devices provide a parameter to choose whether the role of the Ethernet interface is static and defined by the interface configuration (rx-sync-preference of wire-interface-configuration) or whether it must be driven by the SSM protocol.

The current model doesn't seem to provide a parameter like that.

[niloda]

According to this morning's discussion, the clockDirectionDrivenBySssm parameter (boolean with default set to true) is fine for us if only added to the fcPort augmentation.

[openBackhaul]

Decision during the LF ONMI x-haul call on 3rd of April 2024: Two attributes to be added to the FcPort::SyncFcPortSpec class:

• FcPort::SyncFcPortSpec::ssmBasedClockDirectionIsAvail : boolean = false (ro) with comment "If true, the device supports the clock direction being determined by SSM protocol, if enabled by ssmBasedClockDirectionIsOn attribute."
• FcPort::SyncFcPortSpec::ssmBasedClockDirectionIsOn : boolean = false (r/w) with comment "If true, this parameter allows the clock direction on the 1Gbit/s electrical interface to be automatically chosen by the SSM protocol to avoid loops."