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Voice's place in the fiber future

5/21/2007, Joan Engebretson

Incumbent telcos aren't known for acting hastily. While computer industry rivals are famous for rushing products to market without correcting, or even detecting, all the bugs, telcos generally would rather roll out late � but get it right.

In keeping with that attitude, telcos also tend to take small � some might say baby steps � toward end goals. An example is the plan for telcos to deliver voice-over-IP (VoIP) service over the passive optical networks (PON) they have been deploying to support the triple play of voice, video and data services.

The PON, which can carry all three types of traffic natively in packet form over a single fiber connection from the central office (CO) to the customer premises, would seem to be the perfect platform for launching packet-based VoIP service. Doing so could bring operational efficiencies to the telcos and exciting new features to their customers. As usual, telcos are proceeding cautiously in making this move. But four years after telcos began seriously deploying PON, the move to VoIP now appears less than a year away.

Bill Goodman, director of multimedia services architecture for Verizon, the telco that has been most aggressive with its PON deployment plans, shared the company's strategy of migrating PON customers to VoIP � a strategy that continues to unroll in five distinct phases. As Goodman put it, �Our target is moving VoIP further out toward the customer.�

He added, however, that �VoIP isn't the endgame. It's part of it. When you have multiple things sharing network infrastructure, the network is cheaper.�

For several years, Verizon has been using fiber to the premises (FTTP) for green field infrastructure builds � for example, to reach new subdivisions that never before had phone service. In addition, the company has been selectively overbuilding areas already served by traditional copper infrastructure. In green field builds, all customers � even those only taking voice � are served over the FTTP network.

But in overbuild situations, although Verizon ultimately hopes to move all customers onto its FTTP infrastructure, today only customers taking either video or data as part of the company's high-speed FiOS offering are moved onto the FTTP network. In phase one of Verizon's FTTP deployment, those customers received voice service out of an existing Class 5 circuit switch via a GR-303 interface � the same type used to handle voice service through a digital loop carrier.

Today, however, Verizon has moved to phase two, and FiOS customers get voice service through a Nortel Networks' softswitch that operates in TDM mode.

�We wanted to get to the softswitch as quickly as we could,� Goodman said. With the GR-303 interface approach, he noted �the fiber has to terminate on the digital side [of the Class 5 switch], and the movement to the digital side often triggers new ports. At that point, it's cheaper to put in a softswitch.� The softswitch contains a line media gateway, whose function is to convert signaling and media between the VoIP and analog POTS domains, including a session initiation protocol (SIP) user agent.

In phase one and phase two, voice traffic is split off from data and video traffic at the CO, with the data and video traffic moving onto a packet network toward the core while voice is directed onto a traditional circuit-switched network. But phase three, which Verizon is in the process of implementing now, will change that.

�The next phase, and what we're actively working on now, is to move VoIP from the line media gateway to the [optical network terminal] on the side of the home,� Goodman said. �The line media gateway is the greatest cost component of a softswitch. It would be VoIP, SIP-enabled ONT signaling with the softswitch.�

At that point, customers will receive a service that should perform exactly as today's POTS service does but delivered in VoIP form. Voice signals will be in packet form and support SIP signaling from the end user to the CO and will share the same packet network connection as video and data traffic to the network core. To enable customers to use existing POTS telephone equipment within the home, an analog terminal adapter (ATA) is built into the ONT that brings network connectivity to the side of the house.

Although Verizon did not provide specific cost savings, Rob Scheibel, senior marketing manager for Nortel, estimated that the overall move to VoIP can save as much as 50% in capital expenditures and 30% in operating costs. �It eliminates duplicate networks for backhaul and the core,� Scheibel said. �It's more efficient. There's a 20% to 30% reduction in the number of ports because it's dynamically switched versus having to be fixed.�

According to Bruce Ross, vice president of product line management for broadband products for Tellabs, it could be relatively simple for Verizon to upgrade some of its existing FiOS customers to the VoIP-based POTS service. Tellabs, along with Alcatel-Lucent and Motorola, is one of Verizon's suppliers. As Ross explained, most of the ONTs that Tellabs has shipped to Verizon and other customers have SIP capability, which could easily be enabled.

Despite the potential cost savings, however, Goodman said Verizon has not yet determined whether it will upgrade existing FiOS customers currently served with an earlier implementation of voice.

Phase four of Verizon's VoIP migration strategy is where things begin to get interesting for FiOS customers. In this phase, an application server located deeper in the network is added to the mix. The SIP capability built into the ONT, Goodman said, �now would point to a next-generation SIP application server with more advanced features that we've come to know in VoIP-type services.�

Goodman declined to provide details on what those services, known internally as �FiOS voice� might be, other than to say that they would leverage graphical user interfaces and take advantage of bundled voice, video and data services. He also declined to discuss cost but did say that FiOS voice would hit the market within a year as an option for FiOS customers.

One industry analyst who has been closely following telco triple-play rollouts is Teresa Mastrangelo, principal analyst for She offers her take on what FiOS voice and other early incumbent telco VoIP deployments are likely to include. �Call management, unified messaging and presence-related applications will be some of the things they are most likely to offer,� she said.

The challenge in rolling out application server-based VoIP services, Mastrangelo said, is that upstart VoIP providers such as Vonage already have established relatively low price points for feature-rich offerings. The dilemma traditional telcos face, she said, is that �an application server can add features, but will we be able to charge for them?�

Perhaps in recognition of this, Verizon already is plotting its move to phase five of its VoIP-over-PON migration strategy, which adds capabilities that upstart VoIP providers could have difficulty matching. �The last stage is IMS,� said Goodman, referring to IP multimedia subsystem (IMS), a new infrastructure approach that enables key network resources, such as subscriber profiles, to be shared by multiple services and network types.

Verizon ran a request for proposal for IMS last year and is �currently very actively involved with laboratory validations,� Goodman said. The goal of IMS, he said, is to deliver blended services. �As you offer a triple play or quadruple play out of a common environment, where you share media servers and user profiles, they can behave more intelligently together. You get 1+1=3 and a better, well-behaved bundle of services. You also create opportunities to leverage that infrastructure for more third-party development of applications.�

�What's driving people to look at IMS is fixed/mobile convergence or converged mobility,� Scheibel added. IMS can enable what Scheibel calls �voice call continuity,� letting end users hand a call back and forth between a standard cell phone and desk phone. Scheibel added that with an IP network within the home, such as the multimedia over coax (MOCA) capability now offered to FiOS customers, users can add multimedia capabilities such as video calling capability, additional telephone lines and other features.

While the path to phase five for FiOS customers may be clear, Verizon's VoIP migration strategy for its broader customer base still contains many question marks. Although a key driver for deploying PON was to eliminate outside plant costs associated with maintaining copper, Verizon declined to discuss when voice-only customers in PON overbuild areas will be moved to the PON network. And what about the 50% or so of Verizon's network that is not currently slated to receive PON? In keeping with telcos' cautious approach, the fate of those customers likely will depend on what Verizon learns from its experiences with delivering VoIP to FiOS customers.

�As we look five years out, the kinds of things we're looking at are what is the best evolution strategy for the [public network] once there is substantial VoIP and IMS,� Goodman said.

Here, too, IMS is envisioned to play a key role. �With IMS, we have the opportunity, as you have multiple VoIP services, to more efficiently handle VoIP-to-VoIP calls and leverage the synergies across various VoIP offerings,� Goodman said. �That's where we're looking for the next three to five years.�