Methods and messages for performing registration of mobile stations (MS) in an unlicensed mobile access network (UMAN). URR (UMA radio resource) registration messages are exchanged between an MS and a UMA network controller (UNC) operating in the UMAN to register the MS. The MS may access the UMAN via a wireless access point (AP) that is communicatively coupled to the UNC via an IP network. The URR registration messages are sent between the MS and the UNC using an Up interface comprising a set of layered protocols over an underlying IP transport.