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September 1998

Carrier-Grade Voice Over IP Gateways: Meeting The Needs Of The Public Networks


Few technologies have burst onto the scene with the fanfare, promises, and hype as Voice over Internet Protocol (VoIP). Whether it's thought of as simply a means to achieve toll bypass for voice and fax transmission, or as the basis for the next "killer app" (such as unified messaging or the Web-enabled call center), VoIP seems to be part of every network's future these days.

While still very much in the "early adopter" stage with evolving standards, limited interoperability, and immature billing and security infrastructure, VoIP solutions are nonetheless being deployed in both enterprise and public networks. A measure of the promise of this technology is that Voice over IP is the very basis upon which new networks and businesses are being built.

Because VoIP networks need to interface to the Public Switched Telephone Network (PSTN), gateways are required. A VoIP gateway is responsible for converting both call and signaling information between the IP network and the PSTN. Depending on their designated role in the network, gateways can be large or small, simple or complex. For example, some gateways are built on a single PC card, cost-effectively supporting fewer than ten users, where others are "turnkey" solutions designed to adjunct a corporate PBX supporting up to 200 simultaneous callers. Several manufacturers have added VoIP capability to routers and remote access servers so that voice capability can be easily added to an existing private data network.

But what about the public network service providers such as Internet Service Providers (ISPs), Competitive Local Exchange Carriers (CLECs), and traditional telcos? As they integrate IP voice into their networks they face different economic and technical challenges than the enterprise. What are their requirements for scalability, reliability, feature enhancement, and PSTN integration? Are today's PC-based solutions adequate to meet these requirements? To answer these questions, let's examine each of these requirements in detail.

Public service providers are typically faced with the problem of achieving critical mass as quickly and inexpensively as possible. That is, they must first build sufficient infrastructure and provide adequate wide-scale coverage before attracting enough users to generate revenue to recover costs and fuel network growth (the critical mass). Once critical mass is reached, continued network and customer expansion leads to profitability for the service provider.

In other words, when deploying a service such as IP voice, service providers require solutions that will enable them to scale from field trials of a few hundred users to full-scale deployments of several thousand users quickly and economically. Scalability for service providers is only achieved when it encompasses capacity, manageability, and cost-effectiveness. In short, gateways should scale through incremental addition of ports, not systems.

Today's PC-based gateways are typically limited to a few hundred ports of IP voice due to physical slot limitations and because of the number of Digital Signal Processors (DSPs) that can be accommodated in a single chassis. DSPs are critical to gateway scalability because they are the workhorses that perform the voice/packet conversion between networks.

Scaling from a few hundred to several thousand users with PC-based solutions means interconnecting several individual gateways in increments of only a few hundred ports.

This approach is hardly optimal and is certainly not scalable. Utilizing multiple boxes to build large gateways results in excessive hardware, in turn increasing costs and space requirements while decreasing manageability.

Most PSTNs today deliver reliability performance of at least 99.999 percent uptime. This level of performance is then the standard that IP voice must live up to if it is to be adopted by service providers as a mainstream offering. It follows that the gateways that make up IP voice networks must meet this level of reliability.

In order to meet the service providers' stringent reliability requirements, gateways must be designed for fault tolerant operation and be of "carrier-grade." Carrier-grade gateways feature built-in system redundancy and hot swapability. Built-in system redundancy means that no single point of failure either in hardware or software will cause the overall system to fail. Hot swapability of both hardware and software allows a module to be replaced in a running system without taking the system down or losing calls - the very definition of telco reliability.

In addition, traditional service providers such as Regional Bell Operating Companies (RBOCs), Inter-Exchange Carriers, and Public Network Operators will require that gateways deployed in their networks meet existing telco reliability and certification standards such as NEBS, LSSGR, BABT, and JATE.

While significant progress has been made, particularly with regard to the ECTF and its evolving specification of the H.100 telephony bus, PC-based architectures are inherently not carrier-grade. Rather than being designed into the system, redundancy schemes typically involve manual switchover to a hot standby system.

In a competitive marketplace, service providers derive revenue and build customer loyalty through enhanced services. The long-distance market in the United States provides a historical perspective. Initially, the major Inter-Exchange carriers battled for subscribers through continuous price reductions. Inevitably, as prices (and profits) reached rock bottom, competition took the form of feature differentiation. The introduction of voice dialing, single number services, and calling groups, to name a few, were designed to move the customer's focus from price to value - and generate revenue. A similar situation unfolded in the wireless market as competition was introduced. Cellular carriers utilized enhanced services such as prepaid calling cards to maintain customer loyalty, reduce churn, and increase revenue per subscriber.

In today's early market, IP voice service providers are still very much focused on marketing their advantages in the areas of price and voice quality. If history is to be our guide, it is safe to assume that neither of these attributes will remain long-term differentiators. As VoIP network offerings become more widespread, they too will follow the route of the Inter-Exchange and wireless carriers and turn to feature enhancements for their market differentiation and revenue generation.

IP voice service providers will follow the lead of the wireless and the Inter-Exchange carriers worldwide who have turned to open switching platforms, which have enabled them to quickly add services and maintain a competitive edge in a highly competitive marketplace. An open gateway, which supports industry standard Application Programming Interfaces (APIs) such as Microsoft's TAPI 3.0 and S.100 from the ECTF, enables the service provider to choose feature enhancements from a wide selection of software providers.

For public service providers, the ability to initiate and receive calls, anywhere, anytime - whether on their network or off - is mandatory. This means that the service provider's IP voice network must seamlessly integrate not only with other IP networks but also with the PSTN all over the world.

Seamless integration is crucial for the transmission of calls between IP and PSTN networks. Equally important is the smooth transfer of signaling information, which is vital to the preservation across networks of feature delivery such as Call Forward and Call Transfer, as well as enhanced services such as Calling Card and Voice Dialing.

This means that carrier-grade gateways for service providers must be certified to interface with networks of all different vintages all over the world. Trunk interfaces should include T1 and E1 as well as ISDN, which has received certifications such as NET5 (Europe), National ISDN, (US), DASS2 and DPNSS (UK). Signaling protocols such as SS7, DTMF, and R2 must be integrated into the gateway, capable of being easily modified for use with different PSTN networks. Often, signaling and tone plans for older networks are undocumented and vary, often even within the same country.

With the market begging for viable VoIP solutions, vendors of all types, including CLECs, traditional telcos, ISPs, and manufacturers from the voice and data industries, are developing products for this lucrative market opportunity. The programmable switch, when properly engineered, is one product in particular that is ideally suited for deployment as a VoIP gateway. In fact, leading programmable switch vendors are already conducting field trials with a new generation of highly sophisticated, open programmable switches, which have been designed with many critical features qualifying them as formidable VoIP gateways.

The programmable switch vendors that are taking the early lead in the VoIP market, are those that are offering telco-grade, high density, fully open, industry standards-based platforms. For example, some programmable switches can now offer up to 32 DSPs on a single board and over 2,000 compressed IP voice calls in a single platform. By utilizing such a high density and open platform, VoIP service providers will be able to cost effectively scale their gateway solution, while easily adding the necessary enhanced services that the market demands. And since these gateways have open, standards-based interfaces - both hardware and software - they offer unmatched flexibility to the service provider. In addition, these gateways meet the reliability demands of the CO by offering built-in hot swapability and system redundancy. This ensures that the highest standard of network reliability is met.

Similar to the wireless market where cutthroat competition and enhanced services are the rule, the IP voice market will also require gateway solutions capable of quickly shifting with the inevitable market changes and demands. The open programmable switches with the most flexibility offer a critical capability for VoIP service providers that will inevitably depend on enhanced services when competing for customers.

Programmable switches also offer the necessary expertise in complying with international certifications such as NET5, ISDN, DASS2, as well as signaling protocols SS7, DTMF, and R2. With extensive experience utilizing these standards, today's leading open programmable switch vendors have an advantage when coordinating voice communication across IP and PSTN networks. As the VoIP market becomes increasingly crowded with various gateway solutions, look for the 'next generation' of open programmable switches when it comes to meeting VoIP's demanding compatibility, scale, reliability, and network integration requirements.

Peter Carlino is director of business development at Summa Four, a leading provider of open programmable digital switching systems. Today, Summa Four has continued its history of technical innovation, through its pioneering achievements in the open programmable switching marketplace. Summa Four's latest product announcement, code-named Project Sigma, raises the bar in port capacity with the industry's first standards-based open programmable switch. For more information, visit the company's Web site at www.summafour.com.

Next-Generation Integrated VoIP Gateways: Development Issues


First-generation gateways extended tradeshow demo functionality into viable Voice over Internet Protocol (VoIP) solutions. Addressing primarily the Access market, early VoIP gateways featured 2 to 24 ports, enabling Small Office Home Office (SOHO) applications, and some level of enterprise capability to extend voice and fax calls over Frame Relay, ATM, leased lines, Virtual Private Networks (VPNs), and Internet services. Next-generation gateways will extend VoIP services into carrier markets.

The market research firm Frost and Sullivan recently released a report chronicling the evolution of the VoIP gateway from "standalone box" to "integrated gateway." Integrated gateways are platforms that handle the basic gateway functionality in addition to other functions, such as routing and switching. The report suggests that integrated gateways represent the fastest growing segment of the VoIP market. These new integrated gateways will require additional functionality, increased channel density, and Network Equipment Building Standards (NEBS) compliance for superior reliability and manageability in order to be viable solutions in the Carrier marketplace.

Remote Access Concentrators, Remote Access Servers, Carrier class voice/data switching products, enterprise PBXs and enterprise voice/data switching equipment vendors are all expected to provide VoIP solutions. In addressing VoIP implementations, equipment vendors face a common challenge - increasing functionality while maintaining or decreasing product size, at the least possible cost per channel. The core of this challenge lies with the embedded hardware and software solution providing the VoIP functionality. The development of truly carrier class VoIP products hinges on the ability to provide advanced features. These advanced features must include universal access ports (dynamically allocated voice, real-time fax, and data modems on a per call basis), while increasing the amount of traffic each digital signal processor (DSP) can manage, along with redundancy and fail-over features.

Multi-function voice, data, and fax capability (the ability of the gateway to detect non-voice activity and to dynamically allocate the channel and process it accordingly) will be an essential element of carrier class VoIP products. The capacity of the DSPs, that is to say the processing speed defined by MIPs (millions of instructions per second), has a significant impact on how much functionality and performance can be provided by a VoIP solution. Service level features such as Call Detail Records (CDRs), management interfaces, call tracing, performance statistics, and dynamic software configuration will be important as well.

Channel Density
Channel density refers to the number of simultaneous voice channels, handled by the gateway, line card, or DSP. Simultaneous voice channels may be traditional analog lines or DS0s (64 Kbps digital channels). Access Equipment can be expected to ship with 1,000 or more ports. Required channel density has a significant effect on board level real estate and power dissipation. This channel density factor is magnified when redundancy requirements are taken into consideration. Because rack space is limited in most Central Offices, the overall size of the gateway product is an important factor. This size restriction necessitates packaging the maximum number of channels in the smallest space possible. The ability to achieve these channel densities is not only dependent on silicon improvements in DSPs but sophisticated software that can accommodate multi-channel capabilities while accommodating product complexity.

Power Dissipation
In a highly integrated product such as a carrier class VoIP gateway, power dissipation at the gateway, line card and even chip level is an important factor. Significant power dissipation, due to increased functionality, can result in a thermal management issue in a restricted Central Office environment, and could possibly render a solution unacceptable.

Obviously, the cost to implement a VoIP solution (usually measured per channel or port) is a key factor in a gateway vendor's ability to provide a competitive product. This essentially equates to a figure of merit of MIPs per milliwatt, per Dollar. The solution, however, is not straightforward. Fortunately, ongoing advancements in silicon are enabling DSP vendors to continue to increase MIPs and expand architectures, while reducing the size of the DSP as well as the power dissipation per MIP. As a result, there are a variety of DSPs on the market that address these issues. However, the DSPs vary in architectural implementation, impacting the effective execution of a MIP. Comparing MIPs between various DSP architectures is not an effective way to judge tradeoffs. For example, a MIP on one particular DSP may require twice as much memory as a MIP on another DSP, affecting the overall solution cost and size, and ultimately the cost per channel.

Determining the optimal carrier class VoIP solution is tightly coupled between the DSP hardware available and the embedded software solution to run on the DSP. The software implementation techniques, the software architecture, the algorithm optimization approach, and DSP operating system minimization also play key roles in achieving higher channel/DSP densities. The optimal VoIP solution hinges on a well analyzed, integrated system level architecture that has addressed cost, power and real estate tradeoffs, as well as scalability for future enhancements. In order to power next-generation integrated gateways, developers must utilize sophisticated software techniques to take advantage of DSP MIPs, satisfying challenging multi-function, multi-channel requirements.

Debbie Greenstreet is senior product manager at Telogy Networks, a leading provider of embedded software applications to global equipment manufacturers. Telogy's Golden Gateway VoIP software enables manufacturers to develop connected products that can send real-time voice, fax and data over multiple packet networks (such as Internet, Intranet, Frame Relay, and ATM). For more information, visit the company's Web site at www.telogy.com.

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