The killer app for IP

As the deployment of digital subscriber line technology accelerates into the mainstream, it will enable key applications to take advantage of a new generation of high-speed remote access services. One such application is voice over Internet protocol. Voice over IP is particularly attractive to business customers because organizations with telecommuters, remote offices and international offices stand to reap significant savings by minimizing long-distance toll charges and further leveraging their data networks. Eventually, the consumer DSL user will be able to take advantage of this technology. But with any paradigm shift such as voice over IP, there are architectural, user perception and regulatory challenges to overcome.

Just as DSL technology is enabling carriers to provide a new generation of services and time-saving productivity, voice over IP could have the same impact on voice communication in the long term. For the short term, though, a toll-quality or near toll-quality call will require private backbones, not the Internet. The reason for this is the inability to manage key voice-over-IP parameters, including delay, jitter and packet loss across the Internet. Therefore, carriers' early strategy should be to offer voice services to telecommuters and remote offices.

Two architectures, one objective To offer voice-over-IP services to this market, carriers must learn how to combine their DSL and voice-over-IP infrastructures. A typical DSL-based infrastructure consists of a DSL access multiplexer (DSLAM) and a customer premises equipment device. The DSLAM provides the DSL loop termination and the routing of predominantly TCP/IP traffic to the backbone, which is IP, asynchronous transfer mode or frame relay. The CPE device can be either a PC network interface card or a bridge/router device supporting a LAN. Typical offerings include asymmetrical services at speeds up to 7 Mb/s downstream and symmetrical services up to 2 Mb/s both upstream and downstream.

The common components of a voice-over-IP infrastructure include gateway and gatekeeper devices. The gateway, defined by the H.323 standard, provides interconnection of the IP network to the public network, providing functions that include echo cancellation, DTMF tone detection and cancellation, out-of-band DTMF forwarding, fax detection, announcements and call progress tones, call signaling and logging.

The gatekeeper functionality, also defined by H.323, provides the routing information to the gateway devices by interfacing with the SS7 network, analogous to a signal control point. Requiring as little as 6 kb/s of bandwidth and using silence suppression techniques for the transport of true voice information only, voice over IP is quite efficient compared with the traditional 64 kb/s time division multiplexing circuit.

In general, voice traffic can be carried over the data network, originating and terminating as either packetized voice data or a local call. In this case, voice-over-IP traffic is routed over the data network to a gateway that is local to the call's terminating point. There, it is routed to the public network and the local exchange carrier. The gatekeeper provides the gateway devices with the necessary routing information.

With a DSL infrastructure deployed, the resources are available to overlay voice-over-IP technology. The bandwidth provided by DSL technology in the local loop is more than adequate to support the service because voice-over-IP compression and silence suppression techniques require only about 6 kb/s of bandwidth for a call. But more important, with DSL as the transport mechanism, the local access and backbone infrastructure is established to transport voice traffic over the data network (Figure 1).

Applications for voice over IP The most pragmatic near-term application for voice over IP is telecommuting for some fundamental reasons (Table 1). First, telecommuters and remote office users are the dominant early adopters of DSL technology. With DSL, they benefit from orders-of-magnitude improvement in bandwidth.

Telecommuters are now eager to realize additional benefits in the form of value-added offerings such as remote PBX services. Such services allow telecommuters and remote offices to be virtually connected to their corporation's PBX and realize vertical services or Centrex features such as caller ID, three-way calling, visual message indicator and message waiting.

With remote PBX services, voice traffic moves over the data network via gateway devices located in the corporate office and at the remote site. At the remote site, the gateway device can run as a software application on the end user's workstation or as a stand-alone device connected to the DSL modem. Such a device will eventually be integrated into the DSL modem. At the corporate site, the voice-over-IP traffic is routed to a gateway device that provides connectivity to the PBX. This application is not only a true value-added service, but it also meets the requirement of using a private backbone.

Another application in which less than toll quality can be tolerated is the call center. In this application, calls originated from the public network are routed to the data network and, subsequently, to the call center operation. This allows corporations to reduce their operational costs by using their network resources, and it provides a possible means of handling peak-time voice traffic.

Implementation issues The evolution of voice over IP from limited applications to globally available services requires the development and deployment of a standards-based, fully interoperable infrastructure and processes that will provide ubiquitous toll-quality service. The H.323 standard will facilitate this evolution. In addition, key performance parameters that must be globally consistent include delay, jitter and packet loss. These parameters can be guaranteed with service level agreements relying on end-to-end quality of service (QOS) technology that operates not only at the transport layer, but also at the IP layer. ATM layer classes of service such as constant bit-rate and variable bit-rate are well-defined and implemented, but they do not universally extend to the origination and termination point of a voice call. Therefore, IP-layer QOS is required.

The Internet Engineering Task Force is working to converge IP QOS technologies, consolidating resource reservation protocol, DiffServ and multiprotocol label switching technologies and using lightweight directory access protocol as the management protocol. Eventual interoperability of IP layer and ATM layer QOS will allow mass-market deployment, forever changing today's voice call model.

Consolidation with the DSL infrastructure will occur at both the CPE device and the central office. At the customer premises, remote gateway technology and DSL bridge/router modem technology will be integrated, providing both voice and fax capability along with high-speed remote access. In the CO, gateway technology will be integrated with the DSLAM, providing GR-303, DS-1 (1.54 Mb/s) or DS-3 (44.7 Mb/s) interfaces to the public network (Figure 2).

Technology matters aside, the access provider and end user must be able to develop their respective business cases. Can access or service providers realize revenue and profit growth by offering voice-over-IP services to businesses and, eventually, to the mass market as part of their DSL-based offerings? Can the end user, particularly the corporate information technology manager, realize benefits such as operational cost savings through lower cost telephony services or through consolidated network efficiencies? The answer to these questions appears to be yes, as vendors, access providers and IT managers embrace the technology as part of the ongoing consolidation of voice, video and data infrastructures.

Key advantages to integrating voice over IP with DSL technology include:

* Single infrastructure to maintain

* Consolidated services to telecommuters and remote offices

* ADSL infrastructure provides POTS lifeline backup

* Operational cost savings, particularly for international calls

Technologies such as digital subscriber line and voice over Internet protocol have forced the industry to address several regulatory issues. Since the Telecommunications Act of 1996, access to the local loop has been granted to competitive local exchange carriers. The emergence of DSL-based services has led to an ongoing struggle over loop access and co-location between incumbent LECs and CLECs entering their market space.

The emergence of voice-over-IP services has resulted in another debate in the pursuit of broadband services market share. This debate centers on the fact that with voice over IP, interstate and international calls become local calls. The definitions of "service provider" and "voice-over-IP services as information services" are also in question. LECs have taken issue with service providers that offer voice services via a data network while avoiding origination and termination fees for local access.

Also intertwined in this debate is the question of who will contribute to the universal service fund. The position of the incumbents is that as carriers of interstate voice traffic, voice over IP service providers should contribute to the universal service fund and pay the same access charges as long-distance carriers. Long-distance Internet telephony could constitute as much as 13% of total long-distance traffic by 2000.