SS7 in an IMS future
Conventional wisdom has been that the advent of IP Multimedia Subsystem (IMS) networking marks the demise of signaling system 7 (SS7)-based signaling networks. As operators migrate to next-generation architectures, the industry is asking if SS7 is needed, by whom and for how long, says Jeff Key
While the questions in the introduction are legitimate, they are certainly not the most relevant for operators today. Most carriers recognise that two key facts are shaping the reality of next-generation networks. First, the all-IP future, while inevitable, is still a while away. Second, signaling of any protocol – SS7, session initiation protocol (SIP) or others – is critical to operators’ long-term success.
The evolution of SS7-based signaling network infrastructure to SIP-based signaling infrastructure, or IMS networking, does not involve just changing from SS7 to SIP protocols and procedures. It requires a fundamental shift in the network’s design to accommodate more types of services, devices and customer preferences.
But operators aren’t going to give up the billions of dollars invested in their existing networks to achieve these changes overnight. Here are four important considerations as operators make the transition.
SS7 still adds value
S7 is likely to remain the principal signalling technology for years to come. Operators continue to invest billions of dollars each year to maintain and expand their existing SS7 networks and to develop enhanced voice and data services that protect against commoditisation of “POTs” voice service. In fact, almost all of the past decade’s value-added services, including mobility, voice mail, short message service (SMS) and number portability, exist because of SS7 signaling.
As a result, carriers will continue leveraging as much as they can out of their existing signaling networks and investments, and they are more likely to invest in solutions like Sigtran (SS7 over IP) that leverage SS7 before investing in SIP/IMS networks.
Transitional networks
IMS will not succeed if it is an “all-or-nothing” proposition that requires carriers to throw out their existing network equipment. For operators to select an IMS-based solution in today’s cut-throat market, it must improve economics.
Networking is a game of scale: the larger the network, the greater its value to subscribers. By inter-working IMS services with existing services, devices and networks, operators immediately create value. Selecting IMS service infrastructure elements that seamlessly co-exist and inter-work with circuit-switched networks makes economic sense and is critical to the success of IMS.
Signalling the cornerstone
The signalling control layer is a cornerstone of IMS, largely because of the value SS7 signalling has provided to generic dial-tone networks over the past 20 years. Looking ahead, the SIP signalling intensity of multimedia networks will increase dramatically, and experts predict the number and size of SIP signalling messages will increase over SS7 by an order of magnitude.
Signalling will be required to deliver the benefits of IMS — more flexibility in types of services; more tailoring of services to subscriber preferences; and more efficiency in service deployment, fulfillment and assurance.
One solution doesn’t fit all. Operators are at different stages in their IP migration paths and require tailored solutions. These typically combine several “bridging technologies,” which help transition between SIP-based, next-generation networks and existing networks. One solution, a SIP-SS7 gateway, bridges the 2G and 3G networks at the signaling layer. It expands the services and applications available to SS7 and SIP subscribers and enables a larger subscriber base to access those services, driving additional revenue for the carrier.
Another bridging solution, a short message gateway, integrates messaging capabilities between SIP networks and existing mobile networks. It enables the transference of SS7-based SMS messages to SIP and short message point-to-point (SMPP) networks, expanding the potential carrier subscriber base significantly.
Emerging technologies also come into play — unlicensed mobile access (UMA) and fixed mobile convergence enable next-generation VoIP and multimedia services.
The important question facing operators today is not if IMS spells the end of SS7, but how best to leverage existing SS7-based signaling networks, while bridging to SIP-based next-generation networks over the long term.
By selecting today’s real convergence technologies to migrate to all-IP at their own pace, operators can preserve their existing investments and deploy next-gen, multimedia services that generate revenues today.
