The Transition from PSTN to VoIP: Call Routing and User Profiles

ATIS and SIP Forum Efforts for an NNI, Plus a Public Policy Debate

We noted in our blog a week ago that over the next decade, the PSTN (public switched telephone network) as we know it will go away-- replaced by a public VoIP infrastructure.  While the economic and feature benefits are abundant, so too are the potential pitfalls.  One of the biggest obstacles is that the current PSTN serves as one giant gateway for other VoIP services that may otherwise be incompatible, allowing for call routing and different voice codecs at source and destination to interoperate because they both use the PSTN in the middle. 

To address our concerns, we spoke recently with experts at AT&T about their plans to make the transition to an all IP infrastructure.  As we discussed in our blog last month, AT&T has petitioned the FCC to trial an all-VoIP network in two cities, and the company has publically spelled out many of their plans in an FCC filing.  From our perspective (based on public statements and preliminary rulings) the FCC seems very supportive of such a PSTN transition to VoIP. 

With the SS7 network scheduled for replacement, one issue that must be addressed is call routing.  In our conversation with Hank Hultquist, AT&T’s Vice President, Federal Regulatory, he noted that AT&T plans to use SIP as the signaling protocol for call routing.  And to address the need for SIP extensions that will work between carriers, the Alliance for Telecommunications Industry Solutions (ATIS) and the SIP Forum are working jointly on a series of call routing standards for a network to network (NNI) interface and the associated database operational components carriers need.   

Another call routing issue that will need to be addressed is what information will be passed from one carrier to another; this issue is one that is both a public policy question and a technical question.  For those who remember the early days of caller ID enabled by SS7, we recall the public policy debate about whether or not it was a violation of the caller’s privacy to forward names to other carriers when routing the call.  The issue when using SIP and an IMS (IP Multimedia Subsystem) architecture for call routing is even more complex, since a user’s profile in IMS has even more user-specific details (e.g. handset type, personal services authorized) than simply the caller’s name and address/ phone number.  This concern is made more difficult because different countries have different views and laws about privacy. 

We’ll continue our discussion about the transition from the PSTN in the coming weeks, but next time we’ll interrupt our transition coverage for some interesting research about the future of WebRTC. 

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