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The Great Debate
Switches, Servers, and the World of Prepaid
By Robin Tobias |
You purchase a phone card in a store, dial the 800 number, enter
the PIN, and voila – you have made a prepaid phone call. Seems
simple enough, and is probably the way our industry is viewed from
the outside. Those of us who operate on the inside realize that
the technology behind that prepaid call is far more complex. The
latest and greatest in hardware and software run this operation,
and are instrumental to the success of your business. If you are
the underlying telecom carrier providing the service, this backbone
IS your business.
So, you need a solid, reliable, prepaid platform, where do you go?
Just a year or so ago, any techie worth his salt would have recommended
a programmable switch, a TDM-based (Time Division Multiplex) legacy
platform. In prepaid, we have come to know Excel, NACT, Versatel,
and Simplfied as the most common vendors of such platforms. Today,
we have several feature-rich server-based systems available, that
not only provide significant cost savings over programmable switches,
but can process the same call volume. Lately, even some of the programmable
switch vendors have started incorporating server-based systems/functionality
into their offerings, to meet the needs of a changing telecom landscape.
Switches and Servers Defined
“A server-based prepaid platform is a 100% ‘software
platform’ and application utilizing industry standard servers
typically running on Linux, Solaris, or other Unix operating system
variants,” explains Ken Osowski, VP marketing & product
management, Pactolus Communications. “These servers, called
application servers, connect to the Public Switched Telephone Network,
or PSTN, using media gateways (i.e. the switching fabric) through
industry standard IP protocols such as SIP, MGCP, and RTP. These
two components – the application server and media gateway
- form the basis for a next generation server-based platform.”
A TDM-based legacy prepaid platform is made up of a 1) TDM-based
switch and an API for application developers to build prepaid services
to (Excel model), or 2) a TDM-based switch with an integrated prepaid
application that is supplied by the switch vendor (NACT, Versatel
model). In the first case, the applications developed by third party
software developers for a particular switch API are tied to that
switch. Multiple prepaid applications could be available for that
switch from different software developers. When the hardware and
software are integrated, as in the second case, all the prepaid
software and hardware are from the hardware vendor. Versatel Networks
recently acquired Tangerine for its server-based system. Thomas
Howe, CTO of Versatel explains that the programmable switch, “can
be constrained by the limitations of its custom hardware.”
Inherent Differences
Although the user experience is identical, the architectures of
the server-based system and programmable switch are inherently different.
For server-based prepaid platforms, the TDM connectivity is provided
by a media gateway products such as those supplied by Sonus, Telica/Lucent,
Cisco, Sentito and others. The server-based prepaid solution typically
connects to these network elements using the IP-based protocols
SIP and RTP. This separates the switching fabric from the application
giving service providers the ability to choose a server-based prepaid
application and switch hardware independently, assuming that both
interoperate using these IP-based protocols.
“For TDM-based legacy prepaid platforms, the TDM connectivity
is part of the TDM-switch. With the application API tied to the
switch platform defined as a proprietary interface, service providers
would not be able to source an open application framework down the
road that might inter-work with other switch vendors as their needs
change,” says Osowski.
The other components of a server-based prepaid solution typically
include an IP Media Server for IVR, Database Server for management
of subscriber profiles and call record details, and a Web Server
for deploying subscriber portals that enable them to manage their
service features and options.
Bill Kelly, director of marketing for Excel, says, “Excel
has always embraced the app server, media server, media gateway
concept. As you know, prior to any of this terminology even being
around, Excel was a ‘programmable switch’ – essentially
a matrix where all the voice calls, signaling and DSP capabilities
were built in (media server). To control the switch, and deliver
value added services, Excel’s business model has always been
to work with software developers who created applications (like
prepaid), and ran them on a host (application server) that connected
to the Excel via an API. As an all digital platform based on IP,
Excel’s platform evolved to include VoIP (SIP & H.323),
as well as TDM, now making it a media gateway as well – bridging
TDM and IP, wireless, and wireline.” Excel is of the belief
that the “soft” server-based models are best for lower
density networks, in more of a large enterprise type of facility.
“No heavy lifting, like transcoding, conferencing, and interconnection
in the TDM world,” says Kelly.The Benefits
“The primary benefits of server-based systems are that 1)
they give service providers more flexibility in choosing the various
components for a best-of-breed total solution, 2) they typically
embrace Service Creation tools that make it much easier to customize
services or add new features, and 3) upgrading the software environment
to a new price/performance level does not require a ‘fork
lift upgrade’ of the entire system,” explains Osowski.
New computer hardware can be used as it becomes available without
“fork lifting” the application. Howe adds that another
primary benefit is their cost effectiveness in regards to hardware.
“Because server-based prepaid platforms are 100% software
environments with advanced service creation environments, these
systems have already gone beyond the functionality provided for
in TDM switch-based prepaid solutions,” claims Osowski. In
the legacy environments, the switch vendors would have to at least
add new software interfaces, if not hardware interfaces to help
application developers extend their application’s capabilities.
“Again, the decoupling of hardware and software in server-based
solutions using industry standard IP protocols is a huge step forward
in letting service providers and application developers innovate
to meet market opportunities.”
Any service provider can take advantage of this technology, whether
they are servicing subscribers on the PSTN only or have a business
model that also incorporates VoIP. These service providers may offer
only prepaid services like many companies do today, or they can
become full range service providers also embracing VoIP telephony
services, web collaboration with audio conferencing, operator services,
and voice messaging. Osowski adds that “server-based prepaid
platforms are not a one trick pony that deliver only one service.
Service providers can bring many value added services to market
with SIP-based application server approach.”
Costs & Capacity
Systems can start with a hardware investment of as little as $20K
for the server components plus the server-based prepaid software
to form a total solution. Then comes the price of a media gateway,
which can vary widely based on the amount of TDM network connectivity
required. Depending on the vendor, certain features might be included,
with other applications requiring additional licenses.
A single session is required on an application server to support
both the A-leg and B-leg of a prepaid long distance call. This translates
to 2 TDM ports on a media gateway where the call is hairpinned.
Systems commercially deployed have already scaled up to 30,000 concurrent
calls that support several hundred millions minutes of prepaid traffic.
“But this is not the limit since a single Linux server can
support up to 2,000 call sessions and multiple servers can be clustered
to support call volumes well over a billion minutes per month in
a single node,” adds Osowski.
Words of Wisdom
“It is easy for prospective buyers to get a handle on the
technology and how it compares to TDM-based legacy solutions,”
says Osowski. “But getting a handle on the flexibility of
the software environment, the scalability and reliability of the
solution can only be assessed by understanding how this technology
is getting deployed in real world deployments.”
Howe offers, “Start small. Watch your costs and conduct rigorous
testing before you launch the service.”
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