April 2000

BY REG CABLE

To paraphrase Mark Twain, rumors of the death of long-distance telephony as we know it are exaggerated. But not by much. In fact, IP-based telecommunications networking will be the death of old-world long-distance because neither access, transport, nor billing are based on distance � they�re packet-based. While embracing the thundering migration of voice telephony from the established PSTN era to the realm of IP, the datacom world must fully appreciate the value and functionality of a decades-old, telecom-based technology needed to bridge the old and new during the transition � SS7.

Signaling System 7 (SS7), in development since the 1970s, defines procedures and protocols by which PSTN network elements exchange information, out of band, over a digital signaling network to effect call setup, billing, routing, and control. It covers everything from basic call setup, management, and tear down, to wireless services such as PCS, wireless roaming, and mobile subscriber authentication, to local number portability, toll-free services, and enhanced call features like forwarding, caller ID, and three-way calling.

Obviously, these services should be available to callers using either the PSTN or IP networks, so next-generation networks must also rely on SS7. But even as IP calling becomes more prevalent, a huge population of the globe still will be on the PSTN for the foreseeable future. The majority of Internet-service access will still be via the public network, and calls will criss-cross the two camps constantly. Even network builders targeting enterprises with exclusive IP systems will have to accommodate calls routed into or out of the PSTN. SS7 will bridge the two for the next 15�20 years as all-PSTN dedicated trunking networks evolve to all-IP shared bandwidth networks.

GLOBAL REALITIES
Operating companies that can provide global access will ultimately win out. The beauty of the Internet is you can access any server anywhere in the world for the same price. This is why IP telephony will be the death of long-distance as we know it. Telephony will follow the billing model of Internet access � pay for access and performance, not for distance. We�re already seeing long-distance carriers offering �anywhere in North America for five cents a minute� deals. IP-based carriers will be expected to make it �anywhere in the world.�

Next-gen voice-switch builders are realizing the European and Asian marketplaces are opening up even faster than North America, where huge, generations-old investments in PSTN infrastructure must still be amortized. China, for example, is going through an explosive change of its entire network infrastructure, leap-frogging today�s �mixed� technology to fly from old PSTN-like systems directly to next-generation IP models. These markets are most concerned with functionality and are willing to deploy first-generation solutions, whereas the North American market has a quality focus that must be addressed.

As was the case with current wireless service, new IP networks are initially being based purely on functionality, with quality taking a secondary role. The priority, as with first-generation wireless, is global access without distance-based pricing. Demand for quality, however, will soon follow. What starts as a stampede for the cheapest, biggest pipe inevitably becomes insistence on quality and enhanced services. Again, it will be the application of SS7 that will deliver. But a critical problem, often misunderstood, is that not all SS7 protocols are equal � a potential stumbling block that must be addressed immediately.

SS7 VARIANTS
As public switched networks were built up in different countries and regions, SS7 evolved into islands of national and international variants. While IP telephony is based on internationally agreed upon standards, nations developed their own SS7 variants that did not cross borders. The North American standard became the most complex of all, radically different from the rest of the world. This was fine in the �pre-globalized� networking era, but no longer will suffice.

The North American signaling architecture is based on American National Standards Institute (ANSI) standards. Those in most of the rest of the world have been defined by the International Telecommunications Union (ITU). In the meantime, European countries, Japan, and China each have adopted major variant changes within the ITU�s SS7 standard.

First-generation media gateways and media gateway controllers did not include SS7. Subsequent products incorporated SS7 in limited ways, but without concern for overall network optimization. But networks are evolving toward an architecture incorporating stand-alone, full-function SS7/IP signaling gateways driving multiple IP telephony devices (i.e., media gateways, media gateway controllers, and database servers) and providing seamless interaction with the PSTN.

Unfortunately, this global diversity of SS7 is not yet apparent to some next-gen network architects. For example, IP-based softswitches developed using North American standards can not be deployed in France, the entire switch and call model rendered useless. The solution to this dilemma, without having to modify any call-control or media-gateway software, is an SS7-to-IP signaling gateway created to convert French ETSI ISUP to North American ANSI ISUP.

First-generation public-switch vendors such as Nortel Networks, Lucent, Ericsson, and Alcatel need not retrofit their products aimed at systems in countries employing various national SS7 standards if they incorporate SS7-to-SS7 converters. Likewise, IP switch and media-gateway controller manufacturers can create call-control software and SS7-to-IP interworkings, then use SS7 gateways � with SS7 protocol conversion built in � to let them drop their devices into different-flavored SS7 networks around the globe without need for modification.

THE FUTURE
Like it or not, the telephony marketplace is already global. As margins for national long-distance continue to shrink, profits from international calling are swelling. This portends a future where no network is an island because these networks are no longer distance sensitive. Vendors, developers, and systems integrators must have a clear realization that growth potential will be severely limited if their networks are unable to access all variants of SS7 around the world.

Likewise, network builders must break the habit of thinking bigger is better when it comes to the migration to IP, because traditional centralized network architectures geared to large-market applications may not be the most practical or flexible configurations to meet new challenges. In fact, it is a migration toward targeting specific customer segments with niche services deployed closer to the edge of the network rather than on enormous centralized service control points. This future calls for managing services with a larger number of smaller devices, and achieving reliability through redundancy rather than fault tolerance. Signaling gateways can provide the means for this happening.

In any case, voice traffic will continue to migrate from PSTN to IP networks � and expected performance and capabilities will follow. And until the public network eventually disappears, SS7 will be needed to bridge the two universes. Meantime, there will be a parallel evolution of access devices becoming more �intelligent,� able to offer reliable, billable services.

When the �all-IP-all-the-time� epoch arrives, the next generation of SS7 will have evolved into �virtual� signaling, IP-based at the lower layers � SS8, if you will. Until then, the networking industry must fully understand and embrace SS7, a pioneering signaling technology from the last century that will ensure a safe and profitable passage. c

Reg Cable is vice president, Signaling Systems Group, for the MicroLegend Division of Performance Technologies, Inc. (PTI). PTI designs, manufactures, and markets a variety of high-performance networking and communications products for wide-area networking (WAN) and local-area networking (LAN) environments. The company�s subsidiary, MicroLegend Telecom Systems, Inc., is a global internetworking provider of SS7 signaling gateways for major telecommunications carriers and �next-generation� service providers. For more information, visit the company�s Web site at www.pt.com.