Marrying IP, ATM and SONET
By: Michael Vent and Joe Culp
Telecommunications service providers, vendors, manufacturers, analysts and media have been
waging the debate for a few years now. Most carriers and companies have their preference,
but continue to monitor each technology's evolution carefully — even as they migrate older
infrastructures to IP or ATM.
Internet protocol (IP) or asynchronous transfer mode (ATM)?
Or both. More than specific transport technologies, today's service providers are focused on
delivering premium, high speed business services to customers. Network performance,
scalability and cost-effectiveness are of course extremely important to a carrier's business.
But ultimately it is the services and value-added features that generate revenue and increase
market opportunities for service providers, while allowing customers to focus on their primary
business activities.
At IXC Communications, we have essentially put the IP versus ATM debate aside by opting
to use the best technology for the job. As one of the fastest-growing interexchange carriers in
the United States, our business is to provide and manage a wide range of guaranteed,
premium quality services for our customers. And given the distinct capabilities of today's
technologies, the best solution for IXC is a combination of IP and ATM — as well as
traditional SONET.
IXC uses SONET as the standard for its optical core and maps both ATM and IP into that
SONET standard. ATM is used as a predeterministic, quality of service transport service and
IP as a ubiquitous transport service. Each technology is applied based on various
applications. Take for example IXC's Gemini 2000 network, a new nationwide network for
next generation Internet services. The network is designed to run IP into the SONET core
and uses ATM as the collector and transport technology to bring traffic into core hubs.
Together, the three technologies work well to ensure high speed, high quality service delivery.
Maximizing Benefits
By combining IP, ATM and SONET a service provider, and its customers, can get the
maximum benefit from each technology. As they now exist, IP, ATM and SONET each has
its own inherent advantages. ATM is more deterministic in that it has more traffic and policy
features. It also works very well as a gateway technology and has evolved to meet a T1
access requirement from the days when it needed a DS3 pipe. IP is a ubiquitous protocol that
is widely available in homes and offices because it uses standard DSO, time division
multiplexing pipe technology. In addition, IP keeps router traffic in a more native element
domain. And while IP routing and ATM switching both provide Layer 3 protections through
logical restoration, SONET provides physical layer protection by allowing bi-directional line
switching in the case of a severe failure, such as a fiber cut.
Choosing the best technology, or technologies, for a network also depends on customer and
retail service provider requirements. Virtual private networks can be provided over ATM and
soon will be provided over IP. Many enterprises are migrating their networks to ATM-based
switching to transport mission-critical traffic. Even Internet service providers (ISPs) are using
ATM to ensure quality of service. But the truth of the matter is that most customers have yet
to make a final decision on the technology they will ultimately adopt. Therefore it is logical for
a service provider to use the technologies that customers want and to build a core architecture
to support a variety of technology migrations.
Technology Hype
Rationale aside, multiple service networks that support both IP and ATM fly in the face of the
tremendous hype that has always surrounded IP. The industry and especially vendors have
taken zealous positions on IP and have succeeded in bringing the financial community on side.
The hype has been influential to the point that we now have banker and investment
organizations evaluating little known start-up companies solely on the basis of their apparent
IP focus and highly valued ISPs leading world stock exchanges. IP is a good packet
technology, but today it is random and can only deliver “best effort” transport. Until label
switching can be applied to an IP platform, which will then require service providers to move
to a hierarchical network design, its functionality remains somewhat limited.
Despite the traffic issues associated with IP, and the overhead limitations of ATM, the real
irony of the debate is that the technology has never been the true issue. The question is really
about the merits of switching architectures versus routing architectures. All the more
interesting today, as vendors are now introducing their new “router switching” offerings —
solutions which essentially combine the best of both architectures.
A solidly engineered network maximizes available technology and is not built on future
potential or hype. Successful service providers rely on solutions that work well today and can
effectively migrate to the next “best” technology. For IXC customers, IP and ATM work well
together. And SONET, with its physical layer protection and embedded status, is the best
current standard for IXC's service delivery.
Let the engineers and the network architects worry about whether to use IP or ATM in the
edge. Or whether to use ATM in the core and IP in the edge, or vice versa. Focus on
designing a network through the availability of technology and the duration of availability that
gives you the best solutions for the customers that you have now and one that helps you
transition to what the customers want in the future.
About the Authors:
Joe Culp is President of Culp Communications Associates and serves as a consultant to
numerous high technology companies. He is a member of the Newbridge Networks
Chairman's Executive Council and the IXC Communications Board of Directors.
Michael Vent is President of Network Services and Chief Technical Officer at IXC
Communications. |
