This article is excerpted from ATM
Angles for IP Edge, in Network World, 02/15/99, written
by Denise Pappalardo.
At the ATM Forum meeting in the beginning
of February, 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 week 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 because sending traffic over the Internet
isn’t always the most reliable transport method. 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
(Diff-Serv) to ATM. The ATM Forum’s and the IETF’s work
in this arena is new, with technical contributions from the
Diff-Serv working group reaching the forum for the first time
last week. While Diff-Serv defines how to identify a variety
of IP QoS traffic classes, the IETF does not define what makes
up these classes, says George Dobrowski, president of the ATM
Forum and director of broadband networks at Bellcore. The goal
is to define these classes and map Diff-Serv 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
RMOA is another new ATM Forum specification
that is expected to optimize IP video, audio and telephony traffic
traveling over an ATM network, Dobrowski says. 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 says 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.
Originally the ATM Forum touted ATM as the
end-all network solution. Cost and complexity destroyed this
claim. The market also turned to Fast Ethernet and Gigabit Ethernet
as less costly, simpler alternatives. Now it appears that the
forum has changed its tune to one of coexistence and convergence,
says 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 says.
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