how to Send echo message actively

[jinboc]

maybe don't support send echo message ?

[RoadRunnr]

Do you mean PFCP Heartbeat Messages or GTP-U Echo Requests?

• there is no support for outgoing PFCP Heartbeat Requests, yet
• active sending of GTP-U Echo Requests is not supported, yet

Interestingly, there is nothing in 3GPP TS 29.244 that makes GTP-U Echo Request sending mandatory for a UPF or would allow to control the interval of GTP-U Echo Requests through PFCP.
R16 (or so) introduced the GTP-U Path QoS Monitoring. That is an optional feature and support for it would be be indicated by the GPQM flag in the UP Function Features IE.

If you absolutely require active GTP-U Echo sending, then your CP node has to implement that.