For introspection and debugging of a replica set system, it can be helpful to correlate heartbeat requests and responses. Currently we have some logging of request ids in the REPL_HB component, but these request ids are really identifiers that should live in the network command layer. It would be nice if we had heartbeat ids at the replication layer that we could attach to all heartbeat requests. Ids that are unique per node would probably suffice, since we can usually determine sender and receiver information of heartbeat messages.