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Network Node Reference Overview


Network node reference (NetRef) is an extension of the CTP adaptive port clocking. NetRef can be used to provide node level synchronization across a network. NetRef is supported in CTPOS release 5.4R1 and later.

NetRef operates in two modes.

  • Primary or backup operation— When NetRef is configured for primary or backup operation, the primary node sends clocking information to the backup node. The backup node uses an algorithm similar to that used for adaptive port clocking to control the local node clock so that it follows the clocking of the remote node. To operate in primary or backup mode, the remote primary node must be configured as a NetRef primary node with the IP address of the NetRef slave configured. The backup node must be configured as a NetRef backup node with the IP address of the NetRef primary node configured.

  • Adaptive bundle operation— Normally, the adaptive clocking algorithm is used to control the port clock, but when NetRef is configured for adaptive bundle operation, the adaptive clocking algorithm instead controls the node clock. The clocking for the whole node is then derived from the clock that drives the remote port. If the remote port is configured for TT, then the local node is clocked to the remote port's external clock. If the remote port is configured for configured rate, then the local node clock is derived from the remote node clock.

When a node is configured for NetRef backup or adaptive bundle operation, all the external references must be disabled. If timing packets stop arriving at a NetRef backup node , the backup node waits until packets start arriving again to make any clock adjustments. When the packets start arriving again, NetRef transitions to Wait state, waits for 16 packets, and then transitions to the Aggressive state. The LED becomes red when NetRef is in Wait or Aggressive state. The LED is green when NetRef is in Maintain state.

Guidelines for Configuring NetRef

  • You can configure the NetRef adaptive parameters from the port menu. However, you cannot modify the adaptive parameters of a NetRef backup node.

  • If a CTP bundle is already configured between the two nodes, using NetRef adaptive bundle operation does not add to the network traffic between the nodes.

  • Though NetRef is supported only on CTPOS 5.4R1 and later, it supports remote nodes running earlier CTPOS versions. No special configuration needs to be made on the remote node.

  • The maximum number of backup nodes that a NetRef primary node can have is limited to 10. However, there is no limit on the number of backup nodes for the NetRef adaptive bundle operation.

  • Adaptive bundle operation depends on the bundle state and requires a CTP bundle between the nodes. The node synchronization process stops if the bundle comes down. NetRef primary or master operation does not need a CTP bundle between the nodes.