Yesterday, there was only one network – the circuit based network called the public switched telephone network (PSTN). Tomorrow, there will only be one network – the global Internet Protocol (IP) packet switching network called the Internet. Today, we have both networks, and we live in that fascinating time involving the transition from one to the other. The challenges involved in this transition can all be seen, in microcosm, in the transition from Enhanced 9-1-1 (E9-1-1) to Next Generation 9-1-1 (NG9-1-1).

Homes and businesses are increasingly discarding their connections to yesterday’s PSTN. Those “plain old telephony service” connections to the PSTN are being replaced with high speed broadband on copper DSL, cable, and fiber. The same applies in the mobile world. 3G was the last generation of mobile technology that supported native circuit service connections to the old PSTN. 4G networks based on LTE and WiMAX are pure packet based services. Any voice conversations carried out on 4G networks or broadband Internet are, by definition, Voice over Internet Protocol (VoIP).

This transition has a profound impact involving an old familiar concept – the telephone number.

The telephone number is a PSTN concept representing the physical address by which telephone A could reach telephone B. Because the fixed physical point of attachment to the PSTN could be determined by the telephone number, it worked well as a means for determining a caller’s location. Locating a call arriving at an emergency call center was as simple as dipping into a database that related that telephone number to the residential street address to which it was tied.

Even for mobile calls, the telephone number has been tied to a specific physical device tightly coupled to the mobile network to which it was attached. Though mobile callers are not always in one location, they can be found using access network elements. In the world of the Internet, however, a telephone number is no more tied to a physical network location than is an email address or a Skype username. And, so, it should be clear that the challenge supporting emergency calls originating on Internet access (i.e. VoIP calls) includes overcoming a century old, but now misplaced, preconception that telephone numbers are a reliable basis for locating an emergency caller.

It is for this reason that new architectural approaches, related protocols and procedures have been defined to support emergency calling. These specifications, defined by the IETF and NENA, and using protocols like SIP, LoST, and HELD, explain how an IP “call” can be established that is based on audio, text, video or a mix of all. They address the question of how a device can be located in the IP network to which it is attached without any need for presumptions about the meaning of a telephone number – or, indeed, without any need for telephone numbers to be involved at all.

By the same token, as public safety answering points (PSAPs) evolve to support native Internet connectivity using these specifications, they must also support calls made from yesterday’s network. Until tomorrow comes, calls will still originate on plain old telephony service lines and conventional circuit service mobile networks. PSAPs today need solutions that can ensure location information is available whether calls originate on yesterday’s PSTN or tomorrow’s Internet.

CommScope offers products that can support the location of devices on PSTN, all IP mobile networks, fixed residential broadband networks and within enterprise IP LANs. For more information, check out our GeoLENs® Location Information Server.

And let me know – are you ready for the networks of tomorrow?

About the Author

Martin Dawson

Martin Dawson is director of CommScope’s Andrew Solutions’ GeoLENs® Mobile Location Center team based in Wollongong, Australia. Previous to Andrew, Mr. Dawson spent 10 years at Nortel involved in the cellular location industry, working on intelligent network services and wireless intelligent networks. He is a member of the North American National Emergency Number Association (NENA) and co-author of the book IP Location.

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