From Billing World Magazine - "It'll take more than routers with SS7 stacks" to provide "a bridge between the packet and circuit worlds."
Telecom Needs a Bridge, but It Ain't in Brooklyn
Posted November 25, 1998 04:00 AM PST
Data equipment manufacturers are aligning with circuit switching and signaling vendors to supply the hardware and software that will make up the guts of the evolving, multiservice network. Recent deals, such as the one that brought Nortel and Bay Networks together, are evidence of a trend that suggests SS7 will provide the bridge between the circuit and packet worlds to make the vision of a seamless, hybrid network a reality. It'll take more than routers with SS7 stacks, however, to make it happen. Interconnection and internetworking standards must be developed and a host of issues, from security to interconnect billing, must be addressed before services such as direct-dialed voice over IP (VoIP) or on-demand, Web-top videoconferencing can be delivered ubiquitously.
The Value of SS7
People from the data world, who are often accustomed to handling their signaling with an ISDN B-channel, might ask what the point is of connecting to an SS7 network at all. SS7 brings a ton of value to the table, for packet and circuit based service providers alike. SS7, the core of the advanced intelligent network (AIN), is in many ways what makes the PSTN most profitable today.
Without SS7 there would be no caller ID, no 800 services, no calling card services, no number portability; none of these profitable AIN applications. Many consumers depend on these services, and they'll want access to them regardless of what network technology transports their voice and data. Today's VoIP gateways, which translate circuit switched, pulse code modulation (PCM) signals into IP packets, don't support intelligent network signaling. Today's VoIP services are therefore severely limited, not only because they can't support value-added applications, but also because without SS7 capability they require multistage dialing. A VoIP user must first dial the gateway, then enter a PIN number for authentication, and then dial the destination number.
Multistage dialing makes the underlying network technology visible to the user, and it's a pain in the neck, a hassle. Adding signaling capability to these platforms will enable direct dialing and help bring the comforting sound of dial tone to IP networks. This isn't enough, though. To deliver AIN services across hybrid networks, proper AIN triggers must be built into the gateway equipment. "I think that's an area the router vendors need to work a little more on," says Bob Wienski, director of intelligent network services for SS7 network provider Illuminet. "It's important that the protocol between the gateway and the gatekeeper enable the SS7 feature functionality that's inherent in the PSTN. Carriers need to be able to provide service equivalency and seamless service with the PSTN. If they can't do that, then [their offerings] are not going to be very attractive to the end user."
Enough with the Fire and Brimstone
The speed with which data equipment, such as access servers, ATM switches and routers, are being developed with SS7 capability, mainly by recently joined companies such as data equipment developer Ascend Communications and SS7 platform vendor Stratus Computer, has led some in the industry to preach gloom and doom for the signaling network. Some have suggested that SS7-enabled data equipment is being rolled out too fast, and that without proper testing this equipment could cause disasters in the signaling network. These may be the same people who, from uncorroborated evidence, predicted the Earth would be destroyed 20 years from now by a giant meteor.
The only disaster that will occur is for equipment vendors who send unproven products to market. SS7 is an established standard and any equipment that is to be introduced to the signaling network must first go through a stringent, three-stage Bellcore certification process. "We have enough concerns with tested equipment and software bugs with products that have been in the network for five years, and so to even consider allowing a network element to interconnect to the signaling network without being certified would be ridiculous," says Wienski. He adds, "I don't know of any SS7 company that would put their reputation in jeopardy." Wienski does suggest, however, that most of the more mature vendors entering the SS7 market for the first time "realize that they need to be certified by the SS7 network providers prior to going into service." New routers and servers are basically plugged into the Internet every day, but the PSTN has much stricter requirements and its parents, mainly established ILECs and IXCs, are very protective of their profitable, reliable child.
One Size Does Not Fit All
As disparate networking technologies merge, other issues that arise rest on some basic architectural principles. Today's IP-to-PSTN gateways, for example, are designed for low volumes and a relatively small number of ports compared with circuit switching equipment. SS7 links, however, are designed to support circuit switches and thousands of ports. Connecting a small IP-to-PSTN gateway directly to an SS7 network would be like trying to connect a fire hose into a backyard spigot; it just doesn't fit. One way or another, many gateways will need to be concentrated together to maximize a signaling link, but questions of where to incorporate certain functionality remain. An IP-to-PSTN gateway is responsible for converting traditional voice signals into IP packets and vice versa. Multiple gateways are often connected to a gatekeeper that then communicates to the outside world. The gatekeeper is likely to be responsible for converting from an IP standard, such as H.323, to SS7 and thus provide signaling functionality out to the PSTN. This scenario could still raise the fire-hose-to-spigot issue, however, because even a gatekeeper might not be able to fill an SS7 link. Similarly, SS7 network providers, such as Illuminet, aren't really interested in providing the protocol conversions and thus are unlikely to offer traditional gatekeeper services. Wienski says Illuminet has considered the idea of a master gatekeeper to which multiple gatekeepers could be concentrated. This master gatekeeper would speak SS7 only, however, and thus the question remains of who will provide the basic, intermediate gatekeeper functions, especially for smaller providers, such as ISPs getting into the voice game through the small-change window.
Setting the Standards
The fundamental work on standards to enable seamlessness between networks is already under way. Led by IP-based network service provider Level 3 Communications and supported by most of the major data and voice equipment manufacturers, the Technical Advisory Council (TAC) submitted its Internet Protocol Device Control (IPDC) specifications to both the IETF and ITU in August. "The whole concept is to be have the ability to leverage the existing PSTN for access and an IP core network for the backbone transport," explains Scott K. Pickett, CTO and vice president of engineering for integrated voice and data systems developer Vertical Networks and founding member of the TAC. Since the TAC's inception, its goal has been to leverage as many existing technologies and standards as possible to create a robust standard for seamless interconnectivity between circuit and IP networks.
Pickett says that today's standards, such as H.323, don't address trunking very well, which is especially crucial for bringing voice from an IP network into the PSTN and vice versa. "IPDC allows for an SS7 signaled trunk to be controlled by a server function, a soft switch called a media gateway controller. That media gateway controller, over IP, will control a network access device, called a media gateway, to convert PSTN to IP," explains Pickett. As well, the IPDC protocols standardize four specific capability sets: media control, connection control, device management, and signaling transport.
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Excerpted from Telecom Needs a Bridge, but It Ain't in Brooklyn, by Ed Finegold, from Billing World magazine's November 1998 issue. To learn more about billing, customer care, and OSS, visit Billing World magazine on the Web by clicking on their logo at the top of this article. |
