They're at the Gate

Carriers will have to pass through several gateways before VoIP becomes viable.

To paraphrase Mark Twain, the reports of SS7's death have been greatly exaggerated.

As carriers and enterprises develop strategies for moving slowly toward VoIP, however, they are beginning to review their options in terms of hardware, software and structural philosophy to ensure a smooth transition. The key to VoIP is, of course, the intersection between the PSTN and an eventual IP backbone. The primary components of this intersection, where the traffic conversion actually takes place, will be signaling gateways, media gateways and media-gateway controllers.

The media gateway will translate the actual media — calls, faxes, messaging, etc. — from the PSTN to IP packets. The signaling gateway will convert the signaling transport protocol from SS7 to an IP-based standard. Finally, the media-gateway controller, sometimes called a softswitch, will provide call-control functions such as routing, as well as software management of the two gateways.

The signaling gateway is especially vital. According to Samir Marwaha, Inet Technologies marketing strategies director (www.inet.com), the earliest VoIP systems simply made it possible for SS7 signaling to travel over IP networks. Ideally, though, true interoperability between PSTN and IP will come with conversion to IP-specific signaling on that side.

Signaling gateways are beginning to make use of session-initiation protocol, as well as media-gateway-control protocol, to enable signaling traffic truly native to IP transmission. Component providers such as Intellinet (www.intellinet-tech.com) and Performance Technologies (www.pt.com) are focused on stream-control transmission protocol (SCTP), which enables IP signaling, as well as necessary database access.

Eventual winners in the signaling-protocol race will need to provide multihoming, or multistreaming, according to Bob Mason, Performance Technologies director of marketing. This means that a signal is routed along several paths concurrently through IP and is then locked into whichever is currently fastest.

The aggressive use of gateways and gateway controllers has several advantages. First, there is the benefit of distributed architecture. Routing signaling and media traffic across the IP cloud allows for some flexibility in deciding how and where gateways and controllers are physically housed. Developing a call-control and signaling architecture, which is software based, also means that carriers will have more control over purchasing, which can render initial build-out more cost effective than would otherwise be possible.

Separating media gateways from gateway controllers, for instance, ensures that carriers only have to buy what they need, when they need it.

Depending on manufacturer and carrier preference, system hardware, software and administration may be housed in any combination of rack components, dedicated “boxes,” Sun Netra servers or desktop PCs, allowing for more flexibility in procurement and structure. Carriers expect IP networks to be scaleable at large sizes without being redundant at small sizes. That demands flexible configuration, something demonstrated in Nortel's Passport Multiservice IP Portfolio (www.nortel.com) system, according to Terry Boland, Nortel director of wireless Internet core & IP services.

The Pig in the Python

This distributed footprint also makes the network's architecture conceptually similar to the public Internet in many ways, and the gateways actually may make use of public Internet pathways to route connections. This similar design means that centralized control of geographically far-flung elements still is possible through familiar technologies such as SNMP and understandable, Web-based GUI. Distribution also means the footprint is lessened in any one location, according to Anjan Ghosal, Intellinet president & CEO.

Although many carriers have visions of killer apps enabled by IP wireless networks, the most pressing reason for installing signaling and media gateways and the softswitches that manage them may be to survive SMS.

Messaging, and dial-up ISPs to a lesser extent, already is beginning to strain circuit-switched networks. The impetus for much of the current interest in IP conversion will be to offload SMS into the IP cloud and preserve voice trunks for what they were originally designed. Carriers are planning for VoIP, but it doesn't have to happen today. Opening fatter pipes for SMS, the pig in the python, is more urgent. That said, SMS must be accommodated in a cost-conscious way. Mark Milazzo, Cisco director of marketing for mobile wireless (www.cisco.com), said that many carriers underestimated the growth of messaging and now are locked into price structures that don't really account for the additional necessary capital expenditures.

This system has its attraction for carriers but also is being watched closely at the enterprise level. Individual companies are adding gateway functionality to existing communications systems, leveraging the power of existing PBX systems. By converting in-house circuit traffic onto IP paths, and vice versa, IT managers are discovering new ways to keep their people in touch. Avaya (www.avaya.com), for instance, markets its Definity servers and Directory gateway to provide painless remote intranet access; flexible, concurrent routing of incoming call traffic to office, home and mobile numbers; and centralized access to all kinds of incoming messages.

“Initially, I think carriers will use softswitches for transport,” Marwaha said.

Circuit switches are costly, which is why carriers are working to offload data traffic onto IP, but it is also why existing circuit-switched voice trunks will not be abandoned quickly as ways are found for the strain on them to be relieved.

“SS7 is going to be around for a long, long time,” Mason said.

Milazzo also argued that reliance on softswitches as the primary conduit for voice traffic is still in the future.

“Voice works; nobody's going to mess with it, and the risk of reproducing an existing MSC's functionality is pretty huge,” he said.

Where the Buffalo Roam

One area where gateways and softswitches might have an immediate voice application is to extend home coverage areas more cheaply and rapidly. A U.K.-based wireless firm, for instance, could manage a new coverage area in Johannesburg, South Africa, by setting up signaling and media gateways at both ends and using the IP cloud as the connecting fabric in between, rather than having to connect the dots through intermediate STPs.

Performance Technologies markets the Segway to facilitate remote roaming by using IP to connect separate SS7 networks in, for instance, Malaysia and Switzerland, and eliminate the need for SS7 links in between, simplifying “long-haul” traffic. Although a sufficiently fat private IP link between the Segways may be used, security features also can be employed that permit voice traffic over the public Internet, reducing costs further.

As an additional benefit here, the system can be built out without further taxing the dwindling supply of SS7 point codes, according to Mason. The Segways, and similar systems, make use of IP addressing and are no more visible to SS7 architecture than a modem.

Carriers are holding their cards close to their vests in this area so far, and while Qwest (www.qwest.com) plans announcements in the coming weeks, several carriers declined comment for this story. Walt Cole, U.S. Cellular (www.uscc.com) director of network services, was willing to address plans for the integration of gateways into proprietary networks.

For U.S. Cellular, there are concerns with this strategy, and, as usual, standardization and interoperability are among them. The IETF Signal Transport Working Group (www.ietf.org) has coordinated a series of “bake-offs,” in which several companies gather with their latest offerings to test performance of their own variants of SCTP, as well as the interoperability of their equipment. Milazzo explained that carriers are likely to assemble gateways, controllers and software from several major vendors in building VoIP links, not least to minimize slowdowns caused by supply-chain problems. The aptly named “bake-offs,” besides helping manufacturers move toward standardized signaling, also help ensure that it won't be their ingredient that causes the soufflé to fall.

Cole said that he was looking at several different gateways for use by U.S. Cellular. The company is waiting for standardization and interoperability to become more crystallized, but also for some equipment providers to recoup some of their investment costs.

“I will tell you, price makes a big difference,” he said. “If you're not careful, because of where the industry is, you're going to pay for the R&D on a box.”

Obviously, capacity matters. Although the first gateways and soft-switches on the market could perhaps handle 250 calls per second with 30 Sun Netra servers, Inet's VIA soft-switch platform now rates at 1,600 calls per second, and more than 1 million ports on a rack size that can be down to 20% of some competitors' configurations.

Finally, administrative function matters. Is it GUI? Is it command-line? Is it Web-based? What form will the physical interfaces take that the gateway uses to traffic signaling information?

Cole and his counterparts at other carriers still do have some time to ask the right questions and measure the responses to SMS, as well as the demand for video, higher-capacity data transmission, remote administration or voice mail in the Outlook box. One thing is sure, however, looking forward. The python may not be able to eat much more.

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Kintzel (kintzel@sunflower.com) is a freelance writer based in Lawrence, KS.