6/3/98 Upside. ATM vs. IP
Some companies are refusing to take sides. "Others can get into
debates over IP vs. ATM, but we're selling both," says Ascend's Machlin.
upside.com
June 03, 1998
By Jeff Ubois
Two technical issues in the service provider business are
particularly important. One is a concept called Quality of
Service (QOS); the other is how the boundary between
ATM switching and IP routing shifts over time.
As the name implies, QOS involves controlling the level of latency and delay in a network. Anyone who has made an international phone call via satellite can understand why that's important for voice and video on the Net. Nortel's Roth calls QOS "the defining characteristic of advanced networks," and it's a safe bet that QOS will be the enabler for the next killer application.
Carriers would like to offer QOS to their customers because it will
allow them to charge users for different levels of access and service.
Premium prices for QOS will be one way carriers can increase profit
margins for Internet services.
QOS also will ensure reliability. "Large organizations can shave a billion dollars off their private network infrastructures if they can count on the Internet to carry mission-critical traffic," says Steve Pearse, executive VP and general manager for Internet/telecom at Bay Networks Inc. of Santa Clara, Calif. "But for them to trust it, the service providers have to be able to offer service-level agreements and guarantees."
In the meantime, the Internet operates on a "best effort" basis--carriers
do all they can to minimize delays, but latency is unpredictable.
Providing QOS is harder than it sounds, and there's a lot of debate
about how it should be done. How QOS evolves will depend on
changes in the boundary between ATM switching and IP routing.
That's now a religious question for carriers, pundits and equipment
companies, many of which are betting their futures on how it turns out.
Traditional carriers favor ATM, while new carriers such as UUNet
and Qwest favor IP. Similarly, traditional telecom equipment vendors
like ATM better, while most datacom equipment companies, even
those that ship ATM products, prefer IP.
"We dismiss ATM completely. It's not well-optimized for data, and we
don't think it has a long-term future," says UUNet's Taffel. "What
moves people toward ATM is wanting to accommodate isochronous
traffic [two-way traffic without delays] such as voice, but that's a
mistake because voice is irrelevant."
The problem with ATM, Taffel says, is that it can't carry IP traffic
efficiently. Most of UUNet's traffic consists of 64-byte IP packets
traveling between Ethernet LANs. Because ATM uses a fixed-size
(53-byte) cell--visualize a box holding data--sometimes moving data
across an ATM network is like shipping 64 objects using a box that
holds just 53. You've got to send two boxes, one of which is mostly
empty. That means ATM can have high overhead for data traffic,
Taffel says.
And ATM has, in fact, failed to live up to early promises: In particular,
because of high costs and a lack of desktop standards, ATM lost the
battle with IP-based Ethernet to become the standard for desktop
connectivity. Now IP is migrating from the edge to the core of telecom
networks. If that trend continues, it will give an advantage to datacom
vendors.
But other companies argue that IP doesn't provide ATM's network
management, and IP isn't well-suited to carrying mixed traffic such as
voice, video and data. "People talk about the ATM cell overhead or
cell tax," but it's still more efficient than doing voice over IP, says
George Shenoda, CTO of ADC Kentrox, a carrier-equipment vendor
in Portland, Ore. In addition, Asia and Europe have widely adopted
ATM.
Some companies are refusing to take sides. "Others can get into
debates over IP vs. ATM, but we're selling both," says Ascend's
Machlin.
Tommorow! | Bellheads vs. Netheads
Jeff Ubois is an independent consultant who has been digging
through large databases and writing about the Internet for more
than a decade.
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