the present invention is aimed to provide means and methods for recovery of an ip multimedia subsystem ‘ ims ’ where a home subscriber server ‘ hss ’ holding subscriber data for subscribers of the ims has suffered a restart . a first method of recovery is applied after detecting a hss restart , and as receiving a registration from a given subscriber or an invitation to communicate with a given subscriber from another subscriber . a second method of recovery is applied after detecting a hss restart , and as receiving a request from a given subscriber at a s - cscf previously assigned for serving the given subscriber in the ims . both first and second methods may be applied in the ims separately , or in cooperation , following a best effort to ensure that , whatever event occurs first , receiving a registration from a given subscriber , or an invitation to communicate with a given subscriber , or receiving a request from a given subscriber at a s - cscf previously assigned , the actions triggered by the first method or by the second method achieve the recovery of the ims without further actions not applied yet from said second or first methods .