The best BROADBAND VOICE CHOICE

Service providers can serve their markets economically by using voice over DSL

In the past, carriers were forced to deploy separate, costly access networks for delivering voice and data services to subscribers. Multiple voice channels typically are delivered across a TDMA network while data services are best delivered using broadband access networks.

Unfortunately, the TDMA network is not engineered to carry data traffic with maximum efficiency while the broadband access network has not historically catered to the delivery of high-quality voice services.

Now, with ATM-based voice-over-broadband solutions, carriers can deliver bundled voice and data services over a single broadband access network. These solutions can enable competitive local exchange carriers (CLECs), incumbent LECs, interexchange carriers and other integrated communications providers (ICPs) to deliver compelling bundled voice and data services over a single DSL, T-1 or fixed wireless broadband connection to subscribers.

In this article, we consider DSL the broadband access network. The practice of carrying multiple simultaneous voice lines across a single DSL connection is termed voice over DSL. For an ICP, voice over DSL can maximize the copper infrastructure (either owned or rented as an unbundled network element) to provide quality voice services and simultaneously support data applications over the same line. Until recently, DSL was targeted at data communications applications such as high-speed Internet access and remote LAN connectivity. By enabling up to 16 or more telephone lines and high-speed Internet access to be delivered over a single DSL connection, voice-over-DSL systems now allow carriers to apply DSL broadband access networks to one of the biggest challenges they face today: finding a cost-effective method for delivering voice and data services to small and medium-sized business markets.

To date for ICPs, the revenue stream from high-speed data services alone ($75 to $250 per month per subscriber) had to justify the cost of purchasing and co-locating a DSL access multiplexer (DSLAM) in the ILEC central office (CO). With the availability of voice-over-DSL access solutions, however, an ICP now can deliver - over that same access network - local telephone services that could generate an additional $500 to $1000 per subscriber per month. By addressing subscribers' voice and data requirements with DSL service, the ICP can easily make a DSL broadband access network a more profitable service opportunity, dramatically increasing the average revenue per user (ARPU).

The business case for voice over DSL is compelling when delivering bundled voice and data services over a potentially lower-cost network infrastructure - given that the voice services are derived from a Class 5 switch, all existing Class 5 features are supported and a billing system integration is already in place. Alternatively, the voice/data network can be sold as a bundled package, including a fixed number of telephone lines and call minutes, thereby simplifying billing while simultaneously easing disparate network maintenance and reducing access costs. Of course, to be deployed, voice lines derived over packet access networks using voice over DSL must at least match the existing quality of the public network. Years of field testing and early ICP deployments have confirmed that this is the case.

How does it work? Specifically, for voice over DSL, currently available solutions leverage standard ATM and DSL technologies to enable ICPs to deliver from two to 24 telephone lines and high-speed continuous Internet access over a single copper pair.

The first component of a voice-over-DSL solution is an integrated access device (IAD), which resides at each customer premises and uses ATM or frame relay over symmetrical DSL (SDSL) or asymmetrical DSL (ADSL) technologies to multiplex all the subscriber's voice and data traffic onto a single copper pair.

The IAD provides the subscriber with standard local telephone service via analog POTS ports and Internet/data service via a standard Ethernet connection. For ATM across the local loop, voice calls are "ATMized" using AAL2 (real-time variable bit rate) while the data services will be carried as AAL (typically undefined bit rate). All voice circuits share a single permanent virtual circuit (PVC). Data uses another. Correct use of the peak and sustained cell rate parameters for these PVCs guarantees voice calls priority over data - a critical requirement for toll-quality voice solutions. The telephone lines presented at the IAD can be connected to the subscriber's existing telephone equipment, including analog telephones, key telephone systems, fax machines and modems. Analog voice signaling is carried as a message-based protocol - broadband loop emulation service (BLES) - within an ATM cell in the voice PVC. This message based-protocol also provides additional benefits to the ICP for the remote management, provisioning and upgrade of the IAD.

Physical layer connection to the network-based DSLAM is via ADSL, SDSL, ATM25 or even T-1 for subscribers not located within a DSL-enabled service area. For customers who are some distance from the nearest DSLAM, 32 kb/s G.726 adaptive differential pulse code modulation voice compression allows additional voice channels over lower-speed SDSL connections or upstream ADSL connections.

The second component is a standard DSLAM. In an ICP's service architecture, this DSLAM may be positioned at the provider's local facility or co-located at an appropriate third-party site. The DSLAM receives voice and data traffic from each subscriber and concentrates the ATM cells, or frame relay frames, onto a single backhaul facility for transport back to the regional switching center. In addition to enabling efficient service backhaul, DSLAMs are rapidly increasing in port density and dropping in cost. This makes them one of the most cost-effective and flexible types of co-location equipment available.

The backhaul network typically will be ATM-based. An ATM switch receives traffic from each DSLAM, directs AAL5 data traffic to the data/ISP infrastructure and sends AAL2 voice traffic to the final physical component of this voice-over-DSL architecture, the voice gateway.

The voice gateway serves as the mediation point between the ATM access network and the Class 5 switch at the regional switching center. This scalable, highly reliable system presents high-speed optical, standards-compliant interfaces to the ATM switch and high speed electrical standards-compliant interfaces to the switch [GR303]. This GR-303 signaling is terminated by the gateway and subsequently carried to the IAD in ATM cells using the BLES protocol. The voice bearer traffic also is converted to 64 kb/s pulse code modulation and packetized into ATM cells (and vice versa).

For back-office integration, ICPs also require management tools robust enough to allow the service providers to configure their IADs and gateways remotely. Recent service management innovations support ready provisioning for the early adopter customers and include simple operating procedures for mass delivery on subsequent volume service rollout.

Automated systems configure the gateway remotely and provision the IAD via a graphical user interface. Given that network operations typically average costs greater than the original capital equipment expense, management software that can elegantly handle remote element management, configuration and control is necessary for cost containment.

Who's going to use it? Just about all ICPs could reap the benefits of voice over DSL. While the market drivers differ for each segment (CLEC, data CLEC, building LEC, ILEC), all can justify a reason to use this technology both "in" and "out" of territory.

For ICPs to use these systems for delivering toll-quality voice and bundled data services to satisfy the needs of their target customers, the following criteria must be met by any voice-over-DSL solution:

Integrate with subscribers' existing telephone and LAN equipment. If the subscriber must change existing premises equipment, there is typically little incentive to engage a new service provider for voice and data services.

Provide voice quality equivalent to that of traditional local wireline service. When it comes to local dial-tone service, subscribers will not accept voice service that is inferior to the incumbent's service.

Feature availability. Small businesses expect services such as caller ID, call waiting, call transfer and three-way calling. To be successful, the ICP must be able to offer these services at rollout.

From the ICP's perspective, to maximize the profitability of a voice-over-DSL service and increase ARPU, voice-over-DSL solutions must:

Optimize the use of unbundled copper loops. Because copper pairs are typically an expensive and scarce resource, the solution must optimize the use of each copper pair.

Optimize the use of ILEC CO co-location space. To use the ILEC's copper pairs, a CLEC or data CLEC ICP must co-locate equipment in every ILEC CO from which it will provide service. Because co-location space is limited and expensive, the equipment must provide higher densities, a smaller footprint and significantly lower overall cost per subscriber voice port than traditional voice co-location equipment.

Optimize the use of backhaul facilities. The cost of transport services between each serving ILEC CO and the ICP's regional switching center (RSC) can be expensive; therefore, the solution must make efficient use of those facilities.

Optimize the use of existing Class 5 switching equipment. With ICPs making significant investments in expensive, reliable and feature-rich voice and data switching equipment in their RSCs, the solution must enable services to be efficiently integrated with their existing voice and data infrastructure.

Integrate tightly and efficiently with the ICP's provisioning and network management systems. Fully integrated management solutions are required to simplify mass subscriber management and control and to automate flow-through provisioning.

Going further With the early development phase concluded, ICPs now are in position to commence deployment of voice-over-DSL-based solutions and embark on the service life cycle.

As with any product life cycle, there are stages of development, growth and maturity. Voice-over-DSL gateway vendors now are being challenged to deliver multiphase initiatives for key product and service capabilities that map to this voice-over-DSL service life cycle.

In the first phase - development - solutions must be delivered that allow ICPs to scale, upgrade and replace gateway elements without disrupting live user service. In addition, vendors are required to deliver management systems that allow ICPs to define templates and service procedures for configuration provisioning and alarm handling. To accelerate service adoption, suppliers also can add value by providing additional marketing support to the ICP; this may include service bundle definition and business planning, assistance with service marketing concepts, awareness campaign design, sales and support training, public relations support and back-office integration. Given the "gold standard" reliability of voice services, it is critical that vendors also deliver comprehensive customer service, including one-on-one program management, 24-hour support availability, broad e-support, product certification, training and warranty programs.

As the ICP migrates through the second phase - growth - voice-over-DSL solutions must scale for mass subscriber capacity and management. With thousands of IADs now expected to be a part of the network infrastructure, provisioning systems must scale for volume service turn-up, monitor and control. At this stage, the ICP also will embark on a series of niche marketing campaigns as the most popular market segments for bundled services become obvious.

Finally, these voice-over-DSL solutions can enable ICPs to eventually develop service packages that can extend the service life cycle of voice-over-DSL through enhanced service bundles.

For example, in the first phase of the service life cycle, an ICP could profitably supply service packages that include local telephone service at a significant discount and include continuous high-speed Internet access at a minimal charge, if not for free. However, as time goes by, ICPs will need to further differentiate themselves (and combat customer churn) with new classes of products made possible by the mixing of evolving data and voice services.

While voice over DSL enables ICPs to deliver the full suite of supplementary-services today, such as call forwarding, caller ID and Centrex evolution of the gateways into (soft)switching platforms, will facilitate the delivery of a range of new services and applications across the same DSL connection. In this way, ICPs will be able to focus on maximizing the number of services and differentiating themselves through the bundle sold to any given user.