|Carrier-Grade Voice Over IP Gateways:
Meeting The Needs Of The Public Networks
BY PETER CARLINO
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
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,
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
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
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.