Line Card Redundancy for PTP

Line card redundancy is one the PTP redundancy scenarios possible in a mobile backhaul solution. Multiple timeReceiver streams are configured across line cards and if the currently active timeReceiver line card crashes or all streams on that line card lose their timing packets another timeReceiver line card can take over if it has been primed to do so.

When you configure line card redundancy, timeReceiver streams are created on appropriate line cards. At this time all of the line cards are in DPLL mode. All of the timeReceiver streams are primed to receive and process announce messages.

Each line card executes the BTCA algorithm and identifies the best timeTransmitter and the stream serving the best timeTransmitter. The line card sends the best timeTransmitter information to the RE. After receiving best timeTransmitter information from individual line cards, the RE selects the best timeTransmitter to serve the BC node. This information is propagated to all of the line cards. Once the best timeTransmitter is selected by the RE, the regular PTP state machine will be executed.

If the BTCA algorithm results in a stream switchover and the new stream falls on a different line card, a hitless switchover will be triggered. The new timeReceiver card may be configured in pure PTP or Hybrid mode. The old timeReceiver card may in pure PTP timeReceiver or Hybrid timeReceiver mode. The line cards need to go through following steps:

• A timeReceiver line card transition needs to happen via holdover state on the timeTransmitter line card.

• FSM needs to convert the old timeReceiver line card to pure PTP timeTransmitter mode.

• On the new timeReceiver card, FSM needs to be triggered based on pure PTP or hybrid mode of operation. All these transitions need to be hitless.