The Service Location Protocol (SLP) service agent (SA) is a component of the SLP architecture that works on behalf of one or more network services to broadcast the availability of those services.
The SA replies to external service requests using IP unicasts to provide the requested information about the registered services, if it is available.
The SA can run in the same process or in a different process as the service itself. But in either case, the SA supports registration and de-registration requests for the service. The service registers itself with the SA during startup, and removes the registration for itself during shutdown. In addition, every service registration is associated with a life-span value, which specifies the time that the registration will be active.
A service is required to reregister itself periodically, before the life-span of its previous registration expires. This ensures that expired registration entries are not kept. For instance, if a service becomes inactive without removing the registration for itself, that old registration will be removed automatically when its life-span expires. The maximum life-span of a registration is 65 535 seconds (about 18 hours).