Method of exchanging data between a User Equipment, UE and a core network via a security gateway the method comprising the following steps to be performed by the UE: establishing an inactive pair of tunnel mode security associations (120a-120d) between the UE and said security gateway (125a-125c) for an untrusted access network, the establishment including transmission to said security gateway (125a-125c) of a key negotiation message including information that the pair of security associations (120a-120d) is to be in an inactive status; characterized by: establishing a different inactive pair of tunnel mode security associations for a different untrusted access network; detecting attachment to or need to attach to an untrusted access network (130a-130d); determining that the security association pair associated with the untrusted access network is to be applied based upon the detecting of the attachment or the need to attach to the untrusted access network; and applying said established inactive pair of security associations (120a-120d) to user traffic traversing the untrusted network (130a-130d), said applying including transmission of an information exchange message to said security gateway including information that said established inactive pair of security associations (120a-120d) is to be applied. establishing an inactive pair of tunnel mode security associations (120a-120d) between the UE and said security gateway (125a-125c) for an untrusted access network, the establishment including transmission to said security gateway (125a-125c) of a key negotiation message including information that the pair of security associations (120a-120d) is to be in an inactive status; characterized by: establishing a different inactive pair of tunnel mode security associations for a different untrusted access network; detecting attachment to or need to attach to an untrusted access network (130a-130d); determining that the security association pair associated with the untrusted access network is to be applied based upon the detecting of the attachment or the need to attach to the untrusted access network; and applying said established inactive pair of security associations (120a-120d) to user traffic traversing the untrusted network (130a-130d), said applying including transmission of an information exchange message to said security gateway including information that said established inactive pair of security associations (120a-120d) is to be applied. establishing a different inactive pair of tunnel mode security associations for a different untrusted access network; detecting attachment to or need to attach to an untrusted access network (130a-130d); determining that the security association pair associated with the untrusted access network is to be applied based upon the detecting of the attachment or the need to attach to the untrusted access network; and applying said established inactive pair of security associations (120a-120d) to user traffic traversing the untrusted network (130a-130d), said applying including transmission of an information exchange message to said security gateway including information that said established inactive pair of security associations (120a-120d) is to be applied.