It is certainly something we thought might be the case, and so we set our engineers the task of providing redundancy mechanisms for IP communications , based on Aculab's SIP stack, that would enable end customers to build in the reliability they were craving.
Our goal was to enable our customers to build enterprise and service provider communications platforms that could match the reliability and resilience of a legacy TDM-based system, but also give the full unified communications experience made possible by IP.
For over 30 years, designers of TDM networks have taken every step possible to minimise network downtime in search of the mythical 99.999% availability figure (just over 5 minutes downtime per year). The basic rule has been to eliminate any single point of failure. This philosophy has extended beyond simply duplicating the network hardware - separate buildings with separate power feeds and physical connecting cables are also a key part of a resilient network design.
For the IP-core network consisting of routers that are inherently designed to utilise multiple routing paths, this is not an issue; but for hardware attached at the network edge such as media processing servers, it is not so straightforward. An IP-based media server supporting VoIP and video services and using SIP for its signalling is one such platform that sits at the edge of the service delivery network. It is relatively straightforward to duplicate the hardware parts of this server, but not so easy to duplicate the software applications running on the server.
Aculab took on the challenge and created its dual redundant SIP service feature - mirrored SIP stacks are enabled, with failover mechanisms to keep calls active on the standby when the main server fails. The use of a floating IP address with switching to handle the traffic routing to the correct active server provides the mechanism to make sure the traffic is directed to the appropriate server.
If you would like to know more of the detail then you can access our dual redundant SIP whitepaper here.