Interconnect Session Border Controller (ISBC)

This SBC addresses the boundary requirements where service provider networks interconnect and exchange inbound and outbound SIP sessions. It integrates the following three IMS functional elements related to the 3GPP Release 8 ("Exploring IMS security mechanisms"; Acme Packet):

• Interconnect Border Control Function (IBCF): The IBCF offers boundary control between various service provider networks, which provides IMS network security in terms of signaling information. This is done by implementing a Topology-Hiding Inter-network Gateway (THIG) sub-function, which performs signaling-based topology hiding, session screening and IPv4-IPv6 translations based on source and destination signaling addresses. When connecting non-SIP or non-IPv6 networks, the IBCF also invokes the Inter-Working Function and performs bandwidth allocation and admission control using local policies or through the interface to PCRF elements. The IBCF may also interact with TrGW for control of the boundary at the transport layer including NAPT, pinhole firewall, and other features.
• Inter-Working Function (IWF): The IWF provides signaling protocol mechanism between the SIP-based IMS network and other service provider networks, which uses other SIP profiles or H.323.
• Transition Gateway (TrGW): The transport boundary at layer 3 and layer 4 is controlled by the TrGW among various service provider networks having similar media functions as in the AGW.

Multiservice Security Gateway

In the SAE architecture, the Evolved Packet Data Gateway (ePDG) is the functional element, which delivers voice and data services over the un-trusted Wi-Fi networks and Internet to femtocells and dual-mode handsets. The ePDG is responsible to authenticate subscribers and use IPsec to tunnel voice and data securely to devices over the Wi-Fi networks and Internet. For conforming to the 3GPP standards, the ePDG system also supports the I-WLAN Tunnel Terminating Gateway (TTG) functional elements based on the 3GPP Release 7, and UMA/GAN Security Gateway (SeGW) based on the Release 6 and the Femtocell Security Gateway (SeGW) based on the Release 8 specifications.

Session Routing Proxy (SRP)

The SRP deals with interactive communication sessions between SIP network border points, including: SBCs, IMS subscriber call control elements, mobile switching centers (MSC), and controlling media gateways.