FEMTOCELL ARCHITECTURES
There are two broad femtocell architecture approaches within a mobile service provider’s network.         
 
1. All-IP (SIP/IMS): The SIP/IMS based approach integrates the femtocell through a SIP or IMS based network. This approach leverages a SIP based VoIP network for cost-effective delivery, while interworking with a cellular core to extend legacy circuit switched services. In this approach, the CPE converts cellular signals to SIP and interfaces to a SIP-MSC inter-working function (IWF) which connects to the SIP (or IMS) network as well as the circuit switched network.
 
2. Radio Access Network (IP RAN): The IP RAN based approach effectively considers a femtocell an extension into the operator RAN network and ties the femtocell into the circuit switch core at the edge of the network. This typically involves transporting “Iub” messages over IP into a Radio Network Controller (RNC) or a modified RNC/concentrator. (The Iub is the interface used by an RNC to control multiple Node B's in a UMTS network.)

There are three different variants of this approach being pursued by different vendors, however all three of these variants require either the introduction of or major modification to network elements at the RNC layer of the mobile core network:

• Modified RNC: This approach uses existing or modified RNCs to connect to the circuit switched core network. The CPE connects to the RNC via Iub over IP.
• Concentrator: This is similar to modified RAN in that it connects to the CS core, but it does it through a new ‘concentrator’ device that interfaces with the CPE. The interface is again based on Iub over IP.
• UMA: This approach incorporates a UMA client into the CPE and connects to the core network via a UMA UNC.