May 2000

BY ALAN BRIND

For enterprises with sophisticated local area networks (LANs) in place, retrofitting company-wide communications into an IP-telephony model makes sense. It's far more efficient, less expensive and -- despite myths to the contrary -- it's of sufficient quality for business use. But it won't let employees call their mothers or order out from the deli downstairs. Like it or not, the reliable public telephone network must still be involved. Signaling System 7 (SS7) will ultimately be the bridge from the past to the future.

SS7 was originally developed to define procedures and protocols by which PSTN elements exchange information via a packet network -- with signaling carried on a separate overlaid network apart from the actual information flows -- to handle call setup, billing, routing, and control. SS7 covers a wealth of functions, starting with basic call setup, management, and tear down. It handles wireless services such as PCS, wireless roaming and mobile subscriber authentication, and directs local number portability, toll-free services, and enhanced call features like forwarding, caller ID, and three-way calling.

SS7 now is the back-to-the-future technology administrators must use to allow similar services within their IP network, as well as to access all such existing services in the public network from an IP-based network. To compete, any next-generation ISP or CLEC must be able to access the services that exist in the public network that allow for enhanced routing (such as 800-number service or local-number portability) to efficiently transit calls between the IP network and the local carrier of choice. This means they'll need SS7 to initiate queries from within the IP network prior to routing the call into the public switched network.

GLOBAL VIEW
The growth of IP telephony is inevitable and already global in scope. Vendors building next-gen voice switches can see the Asian and European markets blossoming even faster than in North America, where PSTN infrastructure investments are still being amortized. For instance, China is vaulting from old PSTN-like systems past today's "mixed" technology and directly to next-generation IP models. With functionality as a priority, such markets will deploy first-generation solutions.

Spoiled by the PSTN's quality, the North American market will continue to focus on quality of service (QoS). Either way, for IP telephony to compete successfully, SS7 must be deployed to implement popular voice features over data networks.

This expectation of voice over IP (VoIP) growth now challenges LAN-based integrators to accommodate, if not embrace, the WAN world -- even if they're dealing exclusively with enterprise networks.

So, what if you're building an all-IP-all-the-time, strictly internal corporate intranet where everyone within the dial plan is on the IP network? You're still going to need SS7 for any outside call to a non-IP-based telecommunications device -- real-world communications needs, like calling mom.

Enterprise network builders, therefore, must be aware that SS7 capabilities will be in demand for network crossover needs until the world becomes all-IP-all-the-time and everything becomes routing and switching over IP. That will take a while and may never happen exactly the way it's presently envisioned. Nevertheless, all operators and enterprises will be faced with the obligation of mapping IP networks into the PSTN in some way.

SS7 FLAVORS AND GATEWAYS
While there are global international standards for IP telephony, nations and hemispheres have, over time, developed their own flavors of SS7. Developers, integrators, and vendors, therefore, must understand that their potential for growth in the IP telephony marketplace will be hamstrung if their networks cannot access the variants of SS7 that have evolved around the world as various public-switched networks have been built.

Signaling architecture in North America is based on American National Standards Institute (ANSI) standards. The most mature, the North American standard, also has become the most complex and is markedly different from the rest of the globe. SS7 standard in the rest of the developed world has been defined by the International Telecommunication Union (ITU), while many European nations, Japan and China have each developed major variants within the ITU's standard.

While first-generation media gateways and controllers did not include SS7, it has since been incorporated in limited ways into subsequent generations of products. IP-based soft switches developed with one particular SS7 variant, for example, can use SS7-to-IP signaling gateways specifically created to convert one "flavor" to another. Vendors of first-gen switches must incorporate SS7-to-SS7 converters in products targeted at systems in countries using various national SS7 standards.

THE CONVERGED FUTURE
Until the truly next-generation all-IP network emerges (which could possibly be a decade from now) gateways will be the threads that stitch together the patchwork IP/analog network that serve most of us today. While many applications enabled by SS7 probably won't become popular until the market embraces communications devices more mobile than PCs (such as Web phones), savvy vendors and integrators will profit from the demand for emerging SS7 capabilities.

Some vendors are already marketing gateways built with proprietary remote-access concentrators that use signaling to screen traffic so they can offload the data load from crowded voice networks. Ostensibly, such gateways can both ease congestion and accelerate network access times. Others are building software/hardware platforms to afford OEMs the flexibility to create SS7-based systems and applications. Still others offer extensible controller boards packed with intelligence that can be integrated like custom building blocks to maximize performance with minimal cost. The range and diversity of solutions is growing fast.

The convergence of voice and data networks is irreversible. Managing this interim "patched" network world as convergence proceeds will, without a doubt, have interoperability pitfalls, and "who-owns-it" liability questions will be raised and adjudicated. But as a WAN-meets-LAN phenomenon that will be with us for some time, the process of convergence must be accompanied by vendors, integrators, and OEMs who persistantly demand standards and interoperability to ensure smooth internetworking between SS7 and IP networks. That will warrant the emergence of new revenue-generating services to satisfy a market appetite just now being whetted for a promising banquet of capabilities that will mark the converged IP future.

Alan Brind is vice president, marketing and business planning, Performance Technologies. For more information, please visit their Web site at pt.com