The real promise of packet telephony is the ability to
deliver new, value-added services and applications such
as unified messaging, single-number, and location-based
services. If services are to be the future of packet
telephony, a fundamental question must be addressed:
Where will the services be deployed in the network? Will
end-users access services from smart devices at the edge
of the network like SIP phones and PDAs; will carriers
deploy applications from softswitches at the core of the
network; or will applications service providers host
To determine where services should "live" in the
network, several factors must be considered. As the
number of subscribers increases, the overall complexity
and need for capacity increases. The ability to maintain
and manage applications becomes critical as the number
of users and services grow. And, finally, the
applications must be able to interoperate fully with
existing legacy networks and users.
The reality is that there will probably be no single
point of service deployment in next-generation networks.
There are benefits to be realized from all of the
options, and it's likely that service deployment will be
a hybrid of the three. It's going to take a "divide and
conquer" approach to replicate the services that have
taken several decades to develop in the circuit-world.
At the Edge
Devices at the network's edge require two components to
deliver services to the end-user -- a media handler and "smart"
software to handle services. Packet-based devices like
SIP phones, designed as "smart" end points, combine
those essential components into a single device. Black
phones, which just handle media, can be "educated" by
giving them access to intelligence through customer
premise equipment like PBXs or desktop PCs.
It's logical to deploy simple services such as two-
or three-way conference calls from smart end points. The
less-complex applications do not drain network resources
and are easy for customers to manage from their desktop.
When to Take the Next Step
As the service becomes more complex, the number of
services grows, or the number of users increases, it's
time to consider moving the service deployment site
further into the network. While it's relatively easy for
a smart end point to handle a conference call with two
or three legs, the situation changes dramatically when a
user wants to conference in 10 or 20 people. If a
service is deployed from a large number of end points,
it becomes increasingly complex to maintain and update.
As the level of complexity increases, end customers are
less inclined to manage the feature from their desktop.
And, service management for the provider becomes more
To avoid a drain on network resources and simplify
management, it makes sense to move complex applications
into the network. This approach allows providers to take
advantage of economies of scale by sharing the
application or service among many subscribers.
The Network Options
Once the decision is made to locate a service within the
network, several issues have to be addressed. Will the
application reside on a softswitch or an application
server? And, who will control the service delivery --
carriers or third-party application service providers (ASPs)?
The softswitch's role in the new network architecture
makes it a logical point from which carriers deploy
services when the service needs to interact with the
PSTN. It serves as the mediator between the PSTN and the
IP networks providing access to voice and data end
points. It supports both intelligent network and SIP
call models. The SIP User Agent (UA) hosted on the
switch provides "intelligence" to black phones in the
PSTN and emulates SIP behavior on their behalf.
Extending the SIP UA to include value-added service
becomes a natural fit for the softswitch.
Services, which require specialized resources and
service logic, are likely to find a home on dedicated
application servers. Enhanced media processing such as
multi-party conferencing and text-to-speech conversion
can be provided using specialized media servers under
the control of the application servers. This approach
allows providers to customize and quickly deploy
services to match the unique needs of particular
ASPs offer a new model for service delivery and bring
innovation to the market. Third-party development
encourages open, non-proprietary applications and opens
new distribution channels to businesses and end users.
With the ability to purchase services from many
providers, users can get the best application fit by
choosing exactly the services they need to meet their
No matter what architecture prevails, there are
common challenges. Feature interaction has been a major
problem in the PSTN. With more features, multiple
players, and multiple media forms, one only expects this
problem to get more complicated. A modular, scalable
signaling network coupled with service creation and
multiple distribution systems is the foundation required
before the dream of innovation can be fully realized.
Richard (Dick) Hayter is the assistant vice president of marketing for
the Network Systems Division of Tekelec.
Tekelec, a leading supplier of signaling and controls systems, develops
innovative network switching and diagnostic solutions enabling the
convergence of traditional and converged wireline, wireless, and IP voice
and data communications networks. The company also provides products and
solutions for call centers and other telecommunications markets.
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