The transition from fixed-line TDM telephony services to Voice over IP (VoIP) is progressively pushing VoIP’s signaling mechanism - the Session Initiation Protocol (SIP) - even further towards the network edge, encompassing not only trunking and interconnect but also the critical connections between the switching core and the access infrastructure responsible for delivering local subscriber services.
This architectural trend is driven by a number of factors.
While this new reality asserts itself, the old reality of the regulatory requirement for Emergency Standalone, to support critical lifeline and first responder services, remains. Protecting SIP traffic from the impact of lost connectivity to the central core is a key part of ensuring continuity of voice services and in particular access to emergency calling.
Metaswitch’s Emergency Standalone (ESA) Proxy preserves voice calling capability and emergency service access in heterogeneous access networks connected to a SIP core.
Adding ESA functionality into an operator’s network architecture is easy. The ESA function acts as a SIP proxy Registrar, monitoring registrations and building a dynamic database of endpoints, while passing the registrations into the core network Registrar as usual. From mobile clients to BLCs, registered endpoints can include any device that presents an upstream SIP interface to the core network. If the access network loses connectivity with the core network, the ESA Proxy uses its learned registration information to maintain service continuity and call capabilities within its service area.