Diameter native proxy request delivery attempt failed

Logged when a request forwarded by a Diameter backend does not get an answer from the selected member of diameter_peer_group. diameter_upstream_peer, diameter_upstream_adjacency, and diameter_upstream_connection_id identify that member's connection. diameter_delivery_failure is:

• connection-failed: after the request was sent, the connection was lost or became suspect, the request reached its pending deadline, or the routing domain shut down.
• transmission: writing the request to the connection failed.
• pending-limit: the routing domain's pending transaction limit was full.

After connection-failed or transmission, Radiator Server tries the next eligible member, marking retransmissions with the T bit. A full pending store ends forwarding with DIAMETER_UNABLE_TO_DELIVER (3002) and is not retried on another member because the limit is shared by the whole routing domain. diameter_proxy_attempt is initial, failover, or alternate for a retry after a 3002 or 3004 answer.

For connection-failed and transmission, check connectivity to the logged upstream peer and its watchdog events. For pending-limit, compare the request rate and peer response times with maximum_pending_transactions before raising it.