earlier with the following considerations in case of connection to the HeNB GW: Discovery of a suitable serving HeNB GW; A HeNB only connects to a single HeNB GW at one time; If the HeNB is connected to a HeNB GW, it will not simultaneously connect to another HeNB GW or another MME; The Type Approval Code (TAC) and PLMN identifier used by the HeNB is also supported by the HeNB GW [31]; When the HeNB connects to a HeNB GW, selection of an MME at UE attachment is hosted by the HeNB GW instead of the HeNB; HeNBs may be deployed without network planning. An HeNB may be moved from one geographical area to another, and therefore it may need to connect to different HeNB GWs depending on its location. 2.8 Overview of 3GPP evolved packet core network architecture The HeNB GW performs the following functions: Relaying UE-associated S1 messages between the MME serving the UE and the HeNB serving the UE; Terminating non-UE associated S1 procedures towards the HeNB and towards the MME. Note that when an HeNB GW is deployed, non-UE associated procedures are run between HeNBs and the HeNB GW, and between the HeNB GW and the MME and optionally terminating S1-U interface with the HeNB and with the S-GW; Supporting TAC and PLMN identifier used by the HeNB. In addition to functions listed earlier, the MME provides access control for UEs that are members of Closed Subscriber Groups (CSG) in HeNB deployments: a CSG HeNB is only accessible to a group of UEs which are members of the CSG. Access would be denied to the UEs that are not members of CSG, except for emergency services. References [1] Douglas E. Comer, Internetworking with TCP/IP Vol. 1: Principles, Protocols, and Architecture, fifth ed., Prentice Hall, 2005. [2] IETF RFC 3261, J. Rosenberg, H. Schulzrinne, G. Camarillo, A. Johnston, J. Peterson, et al., SIP: Session Initiation Protocol, June 2002. [3] Internet Protocol Security (IPsec), <http://en.wikipedia.org/wiki/Ipsec>. [4] Miikka Poikselka, Georg Mayer, IMS: IP Multimedia Concepts and Services, third ed., John Wiley & S