PFCP heartbeats and headless mode

The following concepts define the connectivity between the BNG UPF and the BNG CPF:

PFCP association
One PFCP association is allowed per BNG UPF and BNG CPF. The identifiers of the association are the BNG UPF and BNG CPF node IDs.
PFCP path
Multiple PFCP paths are possible per association. The identifier of a PFCP path is the pair of IP addresses that are used to communicate between the BNG UPF and the BNG CPF. Paths are not negotiated but are learned while using PFCP signaling.

See UPF PFCP association for information about how PFCP associations are negotiated.

Note: The terms PFCP path and PFCP association are often used interchangeably because there is typically only one PFCP path per PFCP association.

The BNG UPF only uses one IP address, but starts heartbeats for each PFCP path it learns. The frequency, timeout, and retry values of the heartbeats are configured for the PFCP association using the interval, retries, and timeout commands in the configure subscriber-mgmt pfcp association heartbeat context.

If a heartbeat fails, the BNG UPF starts a timer based on the path-restoration-time command configuration under the PFCP association. If the timer expires or is not configured, all sessions associated with that path are removed. If the path recovers before the timer expires, the timer is canceled, and no sessions are removed.

Note: For correct operation, the heartbeat configuration must be identical on both the BNG UPF and BNG CPF. Nokia strongly recommends configuring the path-restoration-time to at least twice the sum of the heartbeat interval plus the total timeout (heartbeat retries x heartbeat timeout = N1 x T1).

To expedite the detection of path failures, enable BFD using the bfd-expedited-path-down command in the configure subscriber-mgmt pfcp association context. When enabled, the system starts a BFD session for each known PFCP path on the BNG UPF. If the system detects a BFD failure, it immediately brings down the associated path. BFD does not affect the path recovery detection, which requires the configuration of PFCP heartbeats. BFD-based path down detection requires the configuration of the path-restoration-time command under the PFCP association.