# Route availability events

The MSPP service supports the following session-level unsolicited events (also called route availability events):

Query | Description
MSPEVN_NOROUTE_AVAILABLE | An RTP or T38UDP endpoint lost the ability to route outbound data to its destination.
MSPEVN_ROUTE_AVAILABLE | An RTP or T38UDP endpoint formerly incapable of transmitting data is now back in service.

Route availability events provide applications with a way to monitor CG board Ethernet interface state transitions. By default, these events are disabled when the application creates the endpoint. If the application initiates multiple MSPP connections (through RTP or T38UDP endpoints) and the Ethernet link remains sound, the application never receives a route availability event. However, if the Ethernet interface fails after any RTP IPv4 or IPv6 duplex or simplex-send or T38UDP endpoint begins transferring data, the application receives an MSPEVN_NOROUTE_AVAILABLE event. If the Ethernet interface recovers, the application receives an MSPEVN_ROUTE_AVAILABLE event.

Route availability events are associated only with data sent over Ethernet connections, not data received over these connections. Therefore, these events do not apply to applications that use only RTP simplex-receive endpoints. Because no data is transmitted, no event is returned even if the Ethernet connection goes down.