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Blowing away the bottleneck

Wed, 02/28/2001 - 7:00pm
David Iler, Contributing Editor


Will Gigabit Ethernet prove to be the secret weapon
that unclogs the broadband pipe?

An early contestant for the most hyped technology of 2001 is actually a network protocol that's been around for almost 30 years. The latest iteration of Ethernet, namely Gigabit Ethernet, is becoming the foundation for a wave of broadband carriers entering the market, and is being proffered by some vendors as a cure for the bandwidth bottleneck blues.

Driving the Gigabit Ethernet bandwagon is the promise of data rates far in excess of what can be delivered through conventional broadband networks, enough bandwidth to satisfy business users and residential power users, and even the Napster-addicted college student.

In January, 360networks and Telseon announced they were creating the first "end-to-end Gigabit Ethernet network in the U.S.," according to a release.

360networks will have access to Telseon's optical Ethernet services in metropolitan areas, allowing it to offer IP transit and backbone services.

Also moving quickly with a Gigabit Ethernet-based network is Yipes Communications. In a short 18 months, Yipes has designed an IP fiber network (by leasing fiber from network providers) in 20 U.S. cities and offers Ethernet connectivity to businesses in increments from 1 megabit per second to 1 gigabit per second. "What we're giving is an extension of the (Ethernet) LAN (local area network) experience to people," says Ron Young, chief marketing officer for Yipes.

The arguments for Ethernet over fiber are many and include the ubiquity of Ethernet LANs in most businesses and the speed by which an Ethernet circuit can be provisioned. "From a business point-of-view, absolutely the biggest legacy device is Ethernet," says Paul Connolly, vice president of marketing and network architecture for Scientific-Atlanta.

And by running Ethernet over fiber instead of copper, the distance limitations of Ethernet are bypassed. "The reason that Ethernet has become ubiquitous," says Octavio Morales, vice president of marketing for World Wide Packets (WWP), "is that it's simple, it's easy-to-use, it's cheap and it continues to evolve to address market needs." Ethernet speeds have steadily climbed from 10 Mbps, with 10 Gbps technologies now under development.

Gigabit Ethernet for HFC?

Harshman

Closer to the world of cable hybrid fiber/coax networks, Harmonic Inc. has been developing Ethernet switch modules that plug into its node platforms, allowing for an eventual migration to a deep fiber architecture. Harmonic's Ethernet systems take part of the HFC delivery network and set it aside "as a true broadband Ethernet network," says Patrick Harshman, president of broadband access networks for Harmonic.

Today's HFC networks usually combine modulated analog video and Data-Over-Cable-Service Interface Specification (DOCSIS) Internet traffic, leaving the headend on a single fiber to be sent downstream. But by mining the optical bandwidth and adding a second wavelength riding in parallel with the DOCSIS and QAM video, operators can deliver high-speed Gigabit Ethernet down to the node level to an Ethernet switch. From the node, fiber is run out to the customer via coax, CAT 5 cable, or singlemode or multimode fiber. (The distance limitations of Ethernet over copper are a factor here.) Potential customers include power residential users (telecommuters, home offices, home offices with Web sites, etc.) and businesses.

From a high capacity router at the headend, the two streams, one Gigabit Ethernet, the other the DOCSIS data, which is combined with video at the cable modem termination system and modulated, are fed into optical transmitters. The Ethernet stream, says Harshman, can be fed into the transmitters that serve specific nodes that serve customers most likely to buy Ethernet service.

"The important thing about this architecture is that not every home is going to want to sign up for 100BaseT or Gigabit Ethernet," says Harshman.

Likewise, some businesses will not opt for video services. "This can be rolled out in a very targeted way," says Harshman.

The two streams can then be multiplexed together through dense wave division multiplexing gear and sent down the network. While the 6 MHz channels of the combined DOCSIS and video stream deliver only 40 Mbps, the pure Gigabit Ethernet streams pack a much bigger punch, and are symmetrical.

By bringing Gigabit Ethernet to the node level, where the DWDM stream is demuxed and the Ethernet stream handed off to a temperature-hardened Ethernet switch, an operator can theoretically offer 10 businesses within that node 100 Mbps Ethernet connections.

Gigabit Ethernet and DOCSIS/video streams can also be transmitted on separate fibers without DWDM.

Harshman says Harmonic is working closely with several cable operators on Ethernet transmission over HFC, including device specific evaluations of customer premises network interface units, Ethernet switches in nodes and optical transceivers and receivers. He hopes to have a beta field trial up and running in late spring or early summer of this year.

In addition to Harmonic, Scientific-Atlanta, using technology from Luminous Networks, in which it has invested, is developing Gigabit Ethernet transmission systems. Connolly says Luminous and S-A are working on a mux/switch/switched router device that can map analog and digital video into a packet-based transport stream.

For operators, the reason Gigabit Ethernet is compelling, says Xiaolin Lu, vice president of IP engineering for AT&T Broadband, is because networks can be developed very fast with off-the-shelf components. Lu says AT&T has the gear at the node to use Gigabit Ethernet for a digitized return path back to the headend, although it isn't at this time.

Acknowledging Ethernet as a transport means in deep fiber architectures, Lu says Ethernet provides a low-cost means of transport, and that piggy-backing or multiplexing Gigabit Ethernet is very much technically feasible. "This is not futuristic stuff," says Lu, who adds that he is looking at the economics of different vendor products.

"If (Gigabit Ethernet transport) is right for our needs, we're certainly going to use it," says Lu, particularly in node areas where Ethernet services would be popular, such as office parks. "If it happens to fit in with our needs, we'll just do it," says Lu, noting that because of the simplicity of Ethernet transport, no trials would be necessary, given equipment that met AT&T Broadband's requirements.

Lu also points out that the lasers that transmit Gigabit Ethernet are of lower cost than those that carry video, which must conform to linearity and signal-to-noise requirements. Gigabit Ethernet at baseband is easy to transport over fiber, says Lu.

Charter Communications, according to Don Loheide, director of engineering/technology, has seen some interest in hospitals, schools, and others in receiving high-bandwidth connections. Gigabit Ethernet "is really following a nice cost curve," he says, yet the company has yet to implement Gigabit Ethernet transport. However, Loheide sees some utility in subdividing nodes using Ethernet from 500 homes passed to 50 for the narrowcasting of video-on-demand and high-speed data, given high takes rates in certain node service areas.

The fast backbone

Besides the applications of Ethernet in the access portion of networks, interconnecting headends is another use of the faster speeds of Ethernet. "We use a lot of Gigabit Ethernet in our systems today," specifically in CMTS interconnects between large systems and for backhaul to large headends, says Milo Medin, chief technology officer for Excite@Home. Gigabit Ethernet, says Medin, is a natural extension of Fast Ethernet, which runs at 100 Mbps.


Figure1: HFC system with parallel Switched Ethernet FTTH network.

Medin notes that as Excite@Home moves to a next-generation caching platform, from Silicon Graphics servers to Linux-based servers running on Intel-powered boxes, Gigabit Ethernet will be the transport protocol for the company's 1,000 points of presence. "We're moving to Gigabit Ethernet across the board," says Medin. "Everywhere you see Fast Ethernet today, you'll see Gigabit Ethernet tomorrow," he adds. However, Medin says that he's using Sonet for the network's trunks because of Sonet's bit-error-rate functionality and for redundancy.

He's less enthusiastic about fiber-to-the-home architectures using Gigabit Ethernet, particularly when the symmetrical nature of Ethernet is cited. "We don't see the asymmetrical nature of DOCSIS as being that much of an issue," says Medin. Rather, it's the degree of asymmetry that's more important. "DOCSIS and the cable network can easily deal with the needs of subscribers," he says.

The missing link: Quality of Service

Harshman admits that one of Ethernet's shortcomings is its lack of Quality of Service provisions. "The truth is, it's still an area of active research," he says.

While Ethernet was not originally designed with Quality of Service, Asynchronous Transfer Mode (ATM), in contrast, is a protocol that was built around QoS.

Harshman believes that Ethernet and Gigabit Ethernet have so much market momentum behind them "it's just a matter of time before it's on parity with other protocols."

For WWP, which has targeted utilities and municipalities with fiber networks, as well as greenfield markets, Ethernet is seen as providing more than raw bandwidth for Internet traffic.

WWP has developed a transport scheme to multicast video using Ethernet. The company, which provides home gateway and network aggregation gear in addition to provisioning and management software, has its hardware with the Grant County Public Utilities District in Washington state and in a small community network in Palo Alto, Calif., which employ fiber-to-the-curb and fiber-to-the-home architectures.

Using an IP-based fiber network architecture, WWP encapsulates single program transport streams and sends individual channels in multicast fashion to subscribers. Each channel is wrapped in an IP frame, then inserted into an Ethernet packet with source and destination addressing at the media access control (MAC) layer.

According to Setty, instead of broadcasting all video channels to all users, only one video stream at a time is sent to subscribers. WWP's hardware and software, says Setty, can assign priorities to video or other traffic using Institute of Electrical and Electronics Engineers (IEEE) 802.1-based priority tags.

Ethernet under wraps

On the horizon for Gigabit Ethernet over HFC is Narad Networks, which counts Rouzbeh Yassini, the architect of Cable Television Laboratories Inc.'s DOCSIS program, as a board member. The company, according to sources, is advocating a 100 Mbps/1 Gbps, symmetric switched Ethernet "overlay" architecture that utilizes the spectrum above 750 and 860 MHz. Company officials contacted for comment declined to discuss Narad's technology at this time.

Perhaps moves by both Yipes and Narad to closely guard how their technology is released publicly reflect the high stakes involved in Gigabit Ethernet-based architectures. With the doppleganger of Internet bandwidth–Napster– creating nightmares for operators, who in their worst dreams are terrorized by a DVD movie version of Napster, quickly bringing more bandwidth to users will become more of a priority.

If anything, Napster and its offspring have proven that bandwidth consumers are "going to fill the pipe if we give it to them," says Setty.

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