Method performed by an Access and mobility Function, AMF interworking with a NF Repository Function, NRF in a 5G supporting Communication Network, CN, providing services to a User Entity, UE, the CN being constituted by a number of network slices, the CN comprising a control plane comprising the Access Mobility Function, AMF, a Session Management Function, SMF, and a user plane comprising a Radio Access Network, RAN, a User Plane Function, UPF, and a Data Network, DN, each DN being denoted by a DN name, DNN, the method comprising - upon receiving a Network, Access Stratum, NAS, message from a UE; - determining that the NAS message corresponds to a request for a new Packet Data Unit, PDU, Session involving a specific DNN; - sending a request for SMF information to the NRF to retrieve at least a list of SMFs that supports the specific DNN and which possible network slices each SMF supports, wherein the request for SMF information comprises a request to retrieve a list of extended information characterized in that the extended information comprises information on which other subscribed DNNs (2B-3) are supported per SMF, the method moreover comprising - receiving from the NRF a response to the request, the response comprising a list of SMFs that supports the requested specific DNN and a network slice, the response comprising the extended information of further supported DNNs, - selecting (2A-3) from the list of SMF's a SMF that supports the new PDU session, wherein the selection of the SMF involves a SMF that - serves the new PDU session involving the specific DNN (2A-3); - supports an optimized subset (2A-4) of subscribed DNNs, wherein the optimized subset of subscribed DNNs is maximizing the number of subscribed DNNs. the method comprising - upon receiving a Network, Access Stratum, NAS, message from a UE; - determining that the NAS message corresponds to a request for a new Packet Data Unit, PDU, Session involving a specific DNN; - sending a request for SMF information to the NRF to retrieve at least a list of SMFs that supports the specific DNN and which possible network slices each SMF supports, wherein the request for SMF information comprises a request to retrieve a list of extended information characterized in that - upon receiving a Network, Access Stratum, NAS, message from a UE; - determining that the NAS message corresponds to a request for a new Packet Data Unit, PDU, Session involving a specific DNN; - sending a request for SMF information to the NRF to retrieve at least a list of SMFs that supports the specific DNN and which possible network slices each SMF supports, wherein the request for SMF information comprises a request to retrieve a list of extended information characterized in that the extended information comprises information on which other subscribed DNNs (2B-3) are supported per SMF, the method moreover comprising - receiving from the NRF a response to the request, the response comprising a list of SMFs that supports the requested specific DNN and a network slice, the response comprising the extended information of further supported DNNs, - selecting (2A-3) from the list of SMF's a SMF that supports the new PDU session, - receiving from the NRF a response to the request, the response comprising a list of SMFs that supports the requested specific DNN and a network slice, the response comprising the extended information of further supported DNNs, - selecting (2A-3) from the list of SMF's a SMF that supports the new PDU session, wherein the selection of the SMF involves a SMF that - serves the new PDU session involving the specific DNN (2A-3); - supports an optimized subset (2A-4) of subscribed DNNs, wherein the optimized subset of subscribed DNNs is maximizing the number of subscribed DNNs. - serves the new PDU session involving the specific DNN (2A-3); - supports an optimized subset (2A-4) of subscribed DNNs, wherein the optimized subset of subscribed DNNs is maximizing the number of subscribed DNNs.