In a recent blog posting (“This is Not Your Father’s Phone Network“, by Adam Roach, June 30, 2009), my Tekelec colleague made a powerful argument that concepts such as SIP to SS7/CAMEL interworking make no sense at all. However, I continue to come across highly knowledgeable telecom professionals from our customer base who see a clear need for it. So, I’d like to present a counter view respectfully disagreeing with my esteemed colleague. Even if one of us may be wrong, a healthy dialogue is always welcome.
The need or lack of need for SIP – SS7 interworking does not arise from the technology, but rather is driven by the business needs. It is an undeniable fact that there are 4+ billion mobile handsets today that are neither SIP-enabled nor served by SIP-enabled mobile switching centers (MSC). Service transparency while roaming is a critical requirement for many operators. This imposes further restrictions in adopting new service delivery technology. These 4 billion handsets follow people wherever they go and offer a potential “instant” market for any type of new service. On the other hand, when we look at the service platforms SIP represents the better option vis-à-vis IN/CAMEL (particularly for real-time services such as voice and video). It provides better future-proofing of investment, offers a more flexible platform that enables quicker rollout of services and offers more subscriber control of the services. The bridging of these two allows operator to use the best technology for the service delivery platform and also provides instant access to the 4+ billion subscribers while at home or while roaming.
It is also important to understand that the need for SIP-SS7 interworking is not to replicate services such as 3-way calling, which are already solved. It is equally true that SIP offers several capabilities that are impossible to replicate in the pre-SIP world. But that should not stop us from identifying services that have common denominators. Numerous services are feasible using basic session control capabilities (Continue with a session, Redirect the session to a different address, Release the session, Play announcement, collect user input etc.) common to both SIP and SS7. Business Voice services such as enhanced private dialing plan, residential Voice services such as parental call control are a few examples that have potential to take advantage of IP technology and provide higher subscriber control and therefore enhanced value. These services can be implemented using SS7/CAMEL, but SIP is a better technology option. It is also practical to map the SIP call control features to the CAMEL call control features for these services.
To address Adam’s next concern – that SIP-SS7 interworking requirements are driving proprietary extensions to SIP – resulting ultimately in SIP failing to deliver on its promise of advanced services. That should not be the way, but unfortunately some SIP extension work does fall into this category. The evolution of SIP should not be hindered by the limitations of SS7, but it should be the other way. A subset of capabilities that is common to SIP and SS7 (as explained above) can be adopted to enhance the services that can be provided to non-SIP subscribers. Meanwhile, it should not exclude the possibility of bringing an avalanche of new IP-based services to a next generation of handsets.
The role of network as a dumb router vis-à-vis network hosted services is not going to be decided by the choice of protocol or technology. It is a business issue and business will find an answer for that and the technology will be the one to follow and adopt it. The answer may be in the middle. A smart handset may be the answer to implement a 3-way call, but network hosted service may be the choice when multi-party conferencing is required. It is possible that a different business model may emerge around a new value chain that involve players providing network pipes, centrally hosted applications and smart clients. Let that not be the reason to prematurely invalidate SIP-SS7 interworking.
In conclusion, the need for SIP-SS7 is not an artificially created need due to the lack of understanding by the telecom industry of the SIP paradigm vis-à-vis the traditional telecom paradigm, but rather the opposite. Most telecom professional recognize that SIP offers the better service delivery platform and are eager to embrace it, but are faced with the challenge of how to make it more relevant to their existing business. SS7 to SIP interworking is a solution, at least in the view of some knowledgeable telecom professionals.