An Access and Mobility Management Function, AMF, of a communications system that comprises an access node, AN, configured to communicate through a wireless air interface with user equipment, UEs, and that comprises a Session Management Function, SMF, the AMF comprising: at least one processor configured to perform operations comprising: receiving an indication of a Max Data Radio Bearer Integrity Protection, DRB-IP, rate indicating a maximum computational capacity of the UE to process DRBs that have integrity protection during packet data unit, PDU, sessions; receiving a packet data unit, PDU, session establishment request non-access stratum, NAS, message from the UE for establishing a PDU session; determining the available DRB-IP rate for which the UE has available capacity for processing DRBs that are integrity protected for the PDU session being established, based on a determined difference between the Max DRB-IP rate of the UE and a summation of DRB-IP rates of flows in any existing PDU sessions that are to be integrity protected by the UE and which are known to the AMF; communicating a PDU session create message toward the SMF; receiving a SMF message containing an indication of an allocated DRB-IP rate for DRBs that are to be integrity protected for a PDU session being established; and communicating a message toward the AN that is communicating with the UE, the message containing the indication of the allocated DRB-IP rate for DRBs that are to be integrity protected for the PDU session being established, wherein the at least one processor is further configured to perform operations comprising: adding the available DRB-IP rate of the UE to the PDU session create message communicated toward the SMF; or constraining the allocated DRB-IP rate that is indicated in the message communicated toward the AN to not exceed the available DRB-IP rate of the UE. receiving an indication of a Max Data Radio Bearer Integrity Protection, DRB-IP, rate indicating a maximum computational capacity of the UE to process DRBs that have integrity protection during packet data unit, PDU, sessions; receiving a packet data unit, PDU, session establishment request non-access stratum, NAS, message from the UE for establishing a PDU session; determining the available DRB-IP rate for which the UE has available capacity for processing DRBs that are integrity protected for the PDU session being established, based on a determined difference between the Max DRB-IP rate of the UE and a summation of DRB-IP rates of flows in any existing PDU sessions that are to be integrity protected by the UE and which are known to the AMF; communicating a PDU session create message toward the SMF; receiving a SMF message containing an indication of an allocated DRB-IP rate for DRBs that are to be integrity protected for a PDU session being established; and communicating a message toward the AN that is communicating with the UE, the message containing the indication of the allocated DRB-IP rate for DRBs that are to be integrity protected for the PDU session being established, wherein the at least one processor is further configured to perform operations comprising: adding the available DRB-IP rate of the UE to the PDU session create message communicated toward the SMF; or constraining the allocated DRB-IP rate that is indicated in the message communicated toward the AN to not exceed the available DRB-IP rate of the UE. adding the available DRB-IP rate of the UE to the PDU session create message communicated toward the SMF; or constraining the allocated DRB-IP rate that is indicated in the message communicated toward the AN to not exceed the available DRB-IP rate of the UE.