ATM angles for IP edge

At the ATM Forum meeting in Atlanta last month, members outlined plans to make ATM the technology of choice for transporting IP traffic over WANs.

The forum’s latest efforts include defining new methods for running IP data, video and voice over ATM. In addition, the forum is teaming with the Internet Engineering Task Force to ensure quality of service (QoS) for IP traffic crossing ATM backbones.

IP traffic flows over ATM backbones today, but the forum wants to go beyond simple transport. The group last month approved its Guaranteed Frame Rate (GFR) specification, a new ATM class of service that lets users more effectively mix Ethernet and IP traffic on an ATM network. The forum’s pending Realtime Multimedia over ATM (RMOA) specification is aimed at bringing reliability to IP voice and video applications.

The forum’s efforts are especially important to business users, such as Georgia Public Broadcasting, that already support ATM and IP in their networks. In the next few months, the public television and radio station is migrating its legacy IPX applications to IP, with plans to add video on demand and voice to its OC-3 speed ATM environment, said Bill Burson, assistant director of IT at the Atlanta-based company.

“When we were building our network, we had certain requirements: It had to grow in easy increments, it had to support standards, and ultimately, it had to support voice and video,” Burson said. “We looked at gigabit Ethernet and other high-speed technologies, but ATM was really the only answer.”

Georgia Public Broadcasting’s IP-over-ATM push has primarily been in its LAN. Transporting IP voice and video over a WAN and the Internet is in the company’s future.

But sending traffic over the Internet isn’t always the most reliable transport method for business users. That’s where the forum’s GFR comes in. Part of the forum’s traffic management specification, GFR will let ISPs offer business users guaranteed minimum bandwidth over the Internet and allow users to borrow from unused bandwidth when it’s available.

GFR will also let customers send traffic that exceeds their guaranteed rate and does not run the risk of losing frames. This is similar to the way carriers provision frame relay service to offer users a committed information rate.

While ISPs offer customers network availability guarantees today, those guarantees are typically not based on a specific technology, and they often don’t guarantee bandwidth.

To foster further QoS developments through the Internet, the ATM Forum and the IETF are working closely to map the IETF’s Differentiated Services (DiffServ) to ATM.

The ATM Forum’s and the IETF’s work in this arena is new, with technical contributions from the DiffServ working group reaching the forum for the first time last month.

While DiffServ defines how to identify a variety of IP QoS traffic classes, the IETF does not define what makes up these classes, said George Dobrowski, president of the ATM Forum and director of broadband networks at Bellcore.

The goal is to define these classes and map DiffServ to ATM to ensure they can work together. The ATM Forum and IETF are working together to establish how the groups’ separate QoS developments can foster a standard that will ultimately bring end-to-end QoS to the Internet.

RMOA is another new ATM Forum specification that is expected to optimize IP video, audio and telephony traffic travelling over an ATM network, Dobrowski said. RMOA defines how to tie together ATM’s variable bit rate (VBR) class of service and the International Telecommunication Union’s (ITU) H.323 voice-over-IP standard. VBR lets users send traffic at a predefined, guaranteed rate over an ATM network. Any traffic that exceeds that rate isn’t guaranteed.

The ATM Forum, the ITU and the IETF are trying to reach a consensus on which version of H.323 they will support. Dobrowski said today there are three versions of H.323, and if the various standards organizations settle on one, users should have less trouble with interoperability and feature support.

The ATM Forum has touted ATM as some sort of network nirvana. Detractors say cost and complexity squelched such claims. The market also turned to fast Ethernet and gigabit Ethernet as less costly, simpler alternatives.

While certainly evangelical about ATM, the forum’s tune has changed to one of coexistence and convergence, said Marlis Humphrey, chairman of the board at the ATM Forum.

Instead of touting ATM as the only network technology users need, the forum is saying ATM is “a superb tool to deliver IP-based services,” she said.

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