acknowledgement message 809 the ipsec tunnel setup and address configuration is performed 421 and the pmipv6 tunnel 423 is established between the epdg 413 and the pdn gw 407 the mme 825 sends a message to release the radio access bearer rab 815 to the 3gpp access network 823 the 3gpp network 823 then acknowledges the rab release 817 the mme 825 releases rab and gtp resources 813 serving gw 403 the serving gw responds with confirmation message 819 tunnel endpoints and radio resources between the pdn gw 407 and the serving gw 403 are released 811 non 3gpp ip access is now established through an ipsec tunnel 425 between the wtru 401 and the epdg 413 and a pmipv6 tunnel 427 between the epdg 413 and the pdn gw 407 the enhanced handover process 900 from 3gpp ip access to trusted untrusted non 3gpp ip access over the s 2 c interface is shown in fig9 a and 9b the wtru 501 is connected to the 3gpp network through the serving gw 503 through a pmipv6 tunnel 505 to the pdn gw 507 when handover is initiated the wtru attaches to the non 3gpp network 511 authentication of the wtru 501 is done by the hss aaa 509 on the 3gpp system ikev2 authorization and tunnel setup 515 between the wtru 501 and the epdg 513 when the non 3gpp network is untrusted alternatively the ikev2 authorization and tunnel setup 516 may occur between the wtru 501 and the pdn gw 507 when the non 3gpp network is a trusted network a proxy binding update message 517 is sent the pdn gw 507 the proxy binding acknowledgement.