Ethernet/SONET debate strong as ever

It is the best of times - technologically speaking - it is the worst of times - from a spending perspective.

And the perfect time for a tale of two networks that may be a prelude to a metro revolution in which the radical young metropolitan-area network (MAN) upstart Ethernet overthrows the old guard SONET.

The SONET vs. Ethernet-in-the-MAN debate was alive and well at SuperComm 2001 two weeks ago, as upstart MAN vendors and service providers extolled the virtues of one, while berating the inadequacies of the other. The quibbling took place against a backdrop of sharply reduced spending among service providers that provided follow-the-money ammunition for both camps.

With data traffic and demand for data services growing, it has become clear to some that the existing, multibillion-dollar SONET infrastructure is incapable of handling such a load. While most MAN players agree that a quick overhaul of this SONET equipment is unlikely, most confer that a change is in store for the way future networks are built.

The most compelling case for Ethernet is its combination of low cost, flexibility, scalability and ease of use, proponents say.

"Every once in a while a great new architecture comes along that, if you could start over from scratch, you'd use the new architecture. That's what Ethernet is today," says Karen Barton, vice president of marketing for Appian Communications, a MAN Ethernet start-up. "Unfortunately, with the existing base of SONET, it's difficult to think about replacing it. Because SONET is so widely deployed, you can build on it."

"Ethernet is in 90 percent of the LANs today," says Burnie Atterbury, Alloptic's senior director of product marketing. "The hardware costs less - it's highly scalable in megabit increments. There is a definite migration happening now, and studies have shown that Ethernet growth is going to be dramatic over the next three years. If you look at SONET growth, it's only small to moderate."

SONET may not be where the growth is, but it's currently where the money is. Optical MAN vendor Astral Point Communications says 98 percent of incumbent local exchange carrier (ILEC) revenue is derived from SONET: 80 percent in voice, 18 percent in packet data services over SONET and 2 percent in native IP.

"What's the likelihood that ILECs are going to take SONET out when that's the case?" says Chris Janson, Astral Point's senior product marketing manager. "We'd rather have the customers than some whiz-bang technology."

"The reality is that SONET is strong," he says. "It's reliable, survivable and there really isn't a limit to its ability to carry data traffic. It's doing just that now."

There is an effort to make Ethernet more reliable, more survivable - more like SONET. That effort is called Resilient Packet Ring (RPR), or IEEE 802.17.

RPR is designed as a high-availability protocol for transporting IP data, packet video and voice-over-ring topologies. Like SONET, it is being developed to support sub-50 msec resiliency.

The technology will complement SONET by replacing SONET's static time-division multiplexing (TDM) with statistical packet switching to add and drop traffic from nodes on the ring, according to the RPR Alliance. RPR initially will be implemented for ring bandwidths of 10G bit/sec and below, but is designed to scale to higher data rates.

The 802.17 standard could be completed in 2003.

Even though it seems Ethernet will eventually take on all of the positive properties of SONET, some MAN Ethernet vendors have begun to hedge their bets. Aura Networks recently announced support for SONET and TDM in its FirstLight architecture; Atrica announced support for SONET with its A-8800 switch; and Alidian says Ethernet services will be supported over a SONET infrastructure, rather than Ethernet uprooting that infrastructure.

It may be that these companies want to tap the ILEC market now that competitive local exchange carriers (CLEC) have mainly bit the dust. Many of these companies initially targeted their product at CLECs.

"At Alidian, we see Ethernet-over-SONET as the data trend of the future," says company Vice President of Marketing Robert Lefkowits. "Major carriers aren't just going to swap out their equipment. ILECs have grown to depend on SONET. They know how to provision services with it, and they've made money doing just that. If it works today, why swap?"

Appian's Barton agrees: "Ethernet technology hasn't quite matured to [SONET's] level yet, but that's part of the RPR initiative," she says. "It's all about migration. RPR is one major initiative to make Ethernet more ready for the metropolitan area LAN-based applications."

Once Ethernet is fortified with RPR, this debate will not likely stop. The next debate will move to ring architectures vs. mesh architectures, and the entire process repeats itself.

"The world is moving away from rings and moving toward mesh," says Alan Brind, Aura's senior vice president of worldwide marketing.

"Nowadays, you can break anything and it will recover," he says.

Out with the old, in with the new?

Benefits, drawbacks of SONET vs. Ethernet Ethernet:

- Scalable in increments from 1M bit/sec to 1G bit/sec and soon to 10G bit/sec.

- Lower equipment costs.

- Versatile -- can support IP services.

- QoS issues exist. Ethernet is not optimized for voice traffic.

- Is not quickly restored in the event of a failure.


- Survivable -- 50 msec restoration. 99.999 percent reliability.

- Optimized for voice traffic.

- Billions of dollars worth of deployed infrastructure.

- Expensive to deploy.

- Is not proficient in carrying data traffic.

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More about AllopticAppian CommunicationsAstral Point CommunicationsAtricaAura NetworksIEEEMegaBitProvisionRPR AllianceSEC

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