Security in intersystem mobility

A method comprising:

• in accordance with the occurrence of a mobility event whereby user equipment moves from accessing a source network to accessing a target network in a communication system environment, a mobility management element of the source network receiving a context request message from a mobility management element of the target network when the mobility management element of the target network is unable to verify the user equipment based on a control plane message received from the user equipment comprising a first integrity verification parameter associated with the target network and a second integrity verification parameter associated with the source network, the context request message comprising the second integrity verification parameter;
• the mobility management element of the source network verifying the user equipment utilizing the second integrity verification parameter;
• and
• the mobility management element of the source network sending a context response message to the mobility management element of the target network responsive to a successful verification of the user equipment utilizing the second integrity verification parameter.