MSRN i.e. Mobile Station Roaming Number, it a a temporary number assigned to a UE or MSISDN so that call can be routed and identity can be protedted as UE is in the new PLMN.
ISISDN or Mobile Station International Subscriber Directory Number is a number used to identify a mobile phone number internationally. MSISDN is defined by the E.164 numbering plan and includes a country code and a National Destination Code which identifies the subscriber's operator.