VoIP Advisor: The Importance of IMS
Bob Dye, VP of Corporate Strategy,
takes you on a quick tour of the industry standard IMS architecture
for converged, wireless-wireline, multimedia networks. He describes
how the IMS architecture differs from traditional networks as well
as its operational benefits for service providers. Drawing from
Sonus’ extensive experience in building carrier-class distributed
architectures for VoIP, Bob discusses how Sonus’ architecture —
first deployed in 1999 — prefigured today’s IMS industry standard.
VA Sonus has announced its products will soon be compliant with the
IP Multimedia Subsystems (IMS) standard. What is IMS?
BD IMS is an architecture, a standard way of describing how to set
up a provider network. Specifically, IMS is a forward-looking
architecture that’s designed to handle the kinds of communications
that service providers will need to deploy and manage over the next
couple of decades.
Voice is completely IP-based on an IMS network, and IMS is built
according to a relatively complete set of standards. This is one of
the few attempts to take a lot of standards and put them in a
package to show how a service provider can construct a complete
network for the future. In theory, a carrier with an IMS network
could buy any component from any IMS-compliant vendor they like, and
it would all work together.
VA How did IMS get its start?
BD The future of voice is VoIP, so it should come as no surprise
that mobile operators and their standards bodies have been trying to
figure out how to handle IP in a mobile world. The original IMS
architecture was defined by the Third Generation Partnership (or
3GPP) program, the group that’s been entrusted with the standards
for GSM, which is the most common mobile standard in the world.
Independently, a similar group called Third Generation Partnership
Program Two, which was responsible for the second most prevalent
mobile standard, CDMA, was working on mobile VoIP.
The two realized that they were working on similar goals, and so
combined their work to form IMS.
VA Why have wireline carriers taken such a strong interest in IMS?
BD Recently, wireline carriers have become very interested in moving
to voice-over-broadband, and, secondly, they know that their circuit
switches are getting long in the tooth. They’ll have to replace them
anyway, so today, instead of buying new circuit switches, they’re
going to VoIP.
Naturally, they’ve been pushing the standards bodies to create a
VoIP architecture. In turn, the standards bodies looked around and
saw that not only was there an IP-based wireless architecture that
needed just a bit of tweaking to work for wireline, but that the
architecture also had the benefit of building a base for fixed-
mobile convergence.
So, ironically, though IMS has its origins in wireless, the wireline
operators may be the first adopters because, as they add wireless to
their portfolio, they will be looking to take advantage of fixed-
mobile convergence.
VA How does IMS enable fixed-mobile convergence, and why is it so
important?
BD Most large, incumbent wireline carriers have a wireless arm, or
at the very least own a substantial interest in a wireless operator.
In the past, service providers tended to have a vertically
integrated network for each application —one for long distance,
another for local service, yet another for mobile. In a competitive
industry, having all of those separate networks is a very expensive
proposition.
What’s more, a lot of carriers are very interested in gaining a
competitive advantage by offering common applications across
multiple services. For example, how nice would it be to have a
shared voicemail box for business, home and wireless?
The ultimate goal is a converged network that would support you and
all your applications no matter how you connect to it. Because IMS
sets out standards for implementing applications of all types on an
IP-based network, once you’ve built that network, it doesn’t matter
how a user hooks up to it.
IMS architecture is ideally suited for this converged network.
VA What’s the advantage of IMS compliance for carriers?
BD The economic advantage of an IMS network over a legacy circuit-
switched network is pretty clear. You get huge operational savings.
We’ve been deploying VoIP, a big part of IMS, in big carriers for
longer than anyone else, and if you compare a typical Sonus
installation to a circuit-switched network, the Sonus installation
uses up to 95 percent less space and pretty much the same ratio for
power, heating and cooling. It’s much, much easier to administer and
allows for the very rapid introduction of new services — something a
circuit switch network cannot offer.
Along with IMS comes the idea of applications that talk to the rest
of the network using IP. It may seem like just a technical nicety,
but it has real business applications.
Applications developed on a siloed, circuit-switched model, for
example, don’t reflect what we’ve learned from standard platforms
like the Internet, where there are huge economies of scale. IMS can
take advantage of these advances because it’s a standard
architecture built for IP. The same technologies used to rapidly
develop websites can be used to rapidly develop voice applications.
VA How is IMS different from what came before?
BD All previous carrier standards grew out of telecom’s circuit
switching legacy. Softswitching and gateway control protocols like
H.248 were simply a way of “decomposing” a circuit switch into
several components. Signaling protocols like Bearer Independent Call
Control (BICC) were simply a way of carrying SS7 information over a
packet network.
In contrast, IMS is based on Internet (that is, IETF) principles and
standards. Intelligence is distributed throughout the network
instead of being centralized in a few circuit switches or
softswitches. Subscriber and routing information is kept in easily
managed central databases instead of being scattered among the
devices that might use that information. All of the call signaling
is based on Session Initiation Protocol (SIP). In short, it looks
very much like the kinds of networks Sonus has been building for
years.
VA What’s the relationship between IMS and Sonus’ Open Services
Architecture (OSA)?
BD When Sonus was founded seven years ago, IMS was just starting to
be developed. There wasn’t a standard architecture for IP-based
networks that would allow third-parties and the service providers
themselves to develop new services on their own, so we created one.
We called it the Open Services Architecture (OSA) and took the lead
in the adoption of Session Initiation Protocol (SIP), which is one
of the foundations of IMS.
But now there is a recognized standard, IMS, so there’s no point in
having a special name for our architecture.
VA What does the IMS architecture look like?
BD IMS defines the functions that a network should provide and how
those functions interact with one another. A good way of thinking
about any architecture, including IMS, is grouping related functions
into “layers.”
In the IMS architecture, each communication is called a session,
whether it be a phone call, a video call, an instant message or
something else entirely. The core of IMS is a set of Session Control
functions to manage all these sessions. These include not only
components that directly handle the sessions, but also the databases
that contain subscriber and routing information.
Next, there’s the Border Management Layer, where all of the
interfaces to the IMS core are managed. Subscribers may be connected
into the IMS network via DSL, cable, metro Ethernet, wireless or a
variety of other technologies, and all of these interfaces must be
managed and controlled. In addition, service providers have to
connect to a lot of other networks, which could be circuit switches,
but could also be IP. They’ll have to manage these connections to
other networks and do so in a secure manner.
Last but not least is the Application Layer, which encompasses the
systems that provide services. These applications communicate with
the network in a standard manner (using the SIP protocol) in IMS.
Finally, there’s a Management Layer where the systems that manage
all of the network components and collect billing information reside.
VA What does the Sonus IMS Solution look like?
BD It looks just like the IMS architecture diagrams! Because the
Sonus solution has always worked according to the principles that
now underlie IMS, it doesn’t take many changes to make it completely
compliant. In several cases, Sonus will divide the functionality
currently supported by one Sonus product into two separate products
to better adapt to the IMS architecture. And, of course, we will
need to add additional subscriber information for wireless users and
the specific message formats associated with them. But we’re talking
about changes that can be accommodated by software upgrades.
VA How will Sonus handle IMS upgrades for current customers?
BD One of the requirements for carrier-grade equipment is the
ability to upgrade software while it’s processing data and calls. If
a Sonus customer wants to go to IMS, we’ll just do a software
upgrade, and they’ll become fully IMS-compliant. For vendors not in
Sonus’ position, IMS compliance will be a much more difficult
proposition for them and their customers.
VA How are other vendors progressing with IMS compliance?
BD There isn’t a lot of hard evidence right now. Every vendor will
tell you they have it, but you have make sure the product matches
the rhetoric.
As products start entering the marketplace, we’ll see who just has
slideware and who has really done the work. We’ve been shipping this
IMS-like architecture for years. Those who haven’t will have to come
up with something new.
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