In addition to the overhead of the timer maintenance itself, the I/O cost of sending keep-alive status messages and the processing of the subsequent replies has a significant impact on CPU utilization when a large number (thousands) of RTP pipes are active. You can use the HPREELIV start option to reduce the CPU impact.

The EE LDLC layer monitors the health of the TCP/IP network underlying the EE connection by monitoring for activity and sending test frames to verify partner reachability. In the event that the partner can no longer be reached, the LDLC layer generates a disconnection for the EE logical connection. For products supporting the architectural option of local link disconnection notifications to drive HPR path switch processing, this means that RTP pipes using EE connections will immediately enter path switch processing if the EE LDLC layer triggers an EE disconnection. Therefore, for RTP pipes that are composed of single EE connections (and including those pipes where the RSCV describes a two-hop path across an EE connection network), HPR ALIVE timer processing is superfluous. As long as the EE LDLC layer has not detected a problem, the RTP partner is considered reachable.

If HPREELIV is set to or defaults to YES, then:

• An RTP pipe with a route composed of a single EE link (including a single hop across a two-hop EE VRN path) can run without an ALIVE timer, thereby relying on the EE LDLC layer for inactivity monitoring, and saving the timer maintenance and keep-alive status request and reply overhead.
• RTP pipes composed of multi-hop paths, or single non-EE hops use ALIVE timer processing as architected.
• An RTP that path switches between one of these types of paths (for example, from single-hop EE to multi-hop) has to dynamically enable and disable the ALIVE timer at the time of the path switch.

There is CPU savings for configurations using HPR-over-one hop Enterprise Extender connections, or two hop Enterprise Extender virtual routing node (VRN) connections. When HPR-over-EE configurations specify DISCNT=NO, significant CPU savings can be achieved. Specifying DISCNT=NO means that HPR and EE connections always stay up, even when there are no sessions.