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GigE Bolsters VOD Transport

Cable engineers don't often borrow technology from another industry, let alone deploy it quickly. Gigabit Ethernet is an exception to both axioms.

Cable operators are using Gigabit Ethernet, commonly known as GigE— a staple in the data communications industry — as a key component in VOD transport.

Data companies developed the technology over several years as a more efficient method to transfer huge amounts of data across networks. Now, Charter Communications Inc., Time Warner Cable and Cablevision Systems Corp. have either said they're using GigE to node quadrature amplitude modulation devices for VOD transport, or are believed to be doing so.

GigE allows a cable system to transmit a greater number of VOD streams to more homes without adding fiber. As operators look to expand VOD content offerings, penetration and usage, GigE is serving as a cost-effective way to reach such goals.

"We're seeing a strong push for GigE going forward," said SeaChange International Inc. executive vice president of strategic planning Yvette Gordon-Kanouff. "It's a lot less expensive to deploy."

Harmonic Inc. has stepped into the GigE space in a big way. It's announced a deal with Charter and several other MSOs for its GIGALight transmission product.

"We think we're the industry leader in GigE," said Harmonic senior director of product management, broadband access division Eric Schweitzer. "We believe it will be the only way people deploy VOD in the future.

"We're pushing GigE as a cost-effective method for VOD and the server vendors are supporting it. ASI [asynchronous serial interface] is less efficient than GigE."

Harmonic digital transport systems product manager Fernando Amendola estimates that about 60 percent to 70 percent of all current servers shipped go out with GigE cards.

Two years ago, Harmonic introduced its narrowcast service gateway for VOD, which was originally designed with an ASI QAM. Current NSGs can also carry GigE QAMs for systems that have made the switch.

"As each month goes by, more GigE QAMs are shipped than ASI QAMs," Schweitzer said. Harmonic said it has shipped about 1,000 NSGs.

"Making [dense wave-division multiplexing] GigE transport that interfaced with the NSGs was logical and easy for us," Schweitzer said.

Each GIGAlight module supports one wavelength.

"We support 32 wavelengths per fiber, which gives you 32 gigabits on a fiber," to lengths as far as 200 kilometers, Schweitzer said. That's key for a company like Charter, which has contiguous medium-sized markets spread across large geographic regions.

"With optical amps, we've done 350 kilometers in a trial," he said.

It's all IP

Although some manufacturers in the telecom space are looking at 10 gigabit technology, Schweitzer believes GIGALight is more efficient because "it's very hard to fill 10 gig data streams efficiently." With GIGALight, operators can add wavelengths in 1-gigabit increments.

By its very nature, GigE is Internet-protocol transport, which is a positive for operators.

"IP has a huge advantage," Schweitzer said. "Gigabit and IP protocols can support long- and short-haul demands using the same physical layer. You can download content to the server wherever it's necessary."

Added Amendola, "Most of time content flows from a server out to a GigE switch, then the GIGALight transport does DWDM transport on one fiber directly into the NSG."

Internet Photonics Inc. is a relatively new entrant into cable's GigE space. It's deployed with one major U.S. operator, believed to be Cablevision Systems Corp.

"Providers are looking for a way to connect servers to hub networks," said Internet Photonics vice president of marketing Gary Southwell. "We're providing GigE transport solution to connect those servers."

GigE allows MSOs to buy fewer node servers and create more centralized VOD library servers VOD, Southwell said.

"You can offer greater numbers of movie selections," he said.

IP's multiplexer can combine eight GigE connections from a server into one 10-gigabit wavelength of light.

"There is a short cable connection from server to an IP Lightstack MX," he said.

The work that telcos have already done on IP will benefit cable operators, Southwell said.

"We've had some advancements on the optical side that we're really bringing to bear," he said. "GigE used to be about small-distance transport."

Marrying the technology to high-quality, low-cost optics has made GigE affordable for cable, he said,

"They couldn't afford what was out a couple years ago."

Southwell estimated that GigE is "about 40 percent more efficient as the number of streams you can get than DVB [digital video broadcast] ASI."

An MSO can get 275 VOD streams on a single GigE wavelength, and IP's Lightstack can spit out 2,000 VOD streams, Southwell said.

"We can get to 30,000 streams with 15 MX units," he said.

IP's transport then interfaces with GigE QAMs from Harmonic Inc., Scientific-Atlanta Inc. and Motorola Inc. at the node. Both S-A and Motorola have GigE transport and QAM products.

Motorola offers operators both a simple streaming solution and more complicated bi-directional switched content distribution GigE products, said Eric Metz, principal engineer at Motorola Broadband Communications Sector.

Motorola's Gigabit Transport Simplex (GTS) product has a multiplexing device that allows MSOs to put two GigE transport streams onto a single wavelength of fiber, Metz said. That fits with MSOs's movement to analyze VOD costs on a per-stream, per-wavelength basis, he said.

"Two ports terminate on our transmission device," said Metz. "We receive it, process it and send it out on ITU grid optics and plug into a 20 kilometer fiber to hub.

"At the hub, we take ITU optics in, receive the signal, demultiplex it and hand it off to remote QAM modulator devices."

Since the industry gets about 240 video streams per GigE port, dual multiplexing allows Motorola to deliver 480 streams in one wavelength, said Metz. Motorola said it has a handful of orders for its GTS product, with testing underway in several MSO labs.

The next evolution of the GTS is a 10-gig port to a 10-Gigabit-per-second ITU grid wavelength, Metz said.

"It's still a simplex device," he said, but it allows MSOs to "drop off" two ports of GigE at, say, three different hub sites.

"Each hub picks off what it needs," Metz said. "You still have the same wavelength number and same number of transceivers. It's the same price as the two gig port."

"Using cost per stream, per wavelength creates a very fixed business model," Metz said. "You just change the number of streams on peak simultaneous usage. MSOs can see exactly the ROI just by typing in number of streams viewed."

Metz said the 10-Gigabit product is in the design phase and would head to lab trials in first-quarter 2003. If employing two GigE ports can cut point-to-point transfer costs by 50 percent to 60 percent from ASI, said Metz, then the 10-gig product would further reduce them by 20 percent to 40 percent.

Go Bi-directional

VOD networks that have grown more complex and a wider web of servers and media and element management systems mean that operators have to start thinking about having enough bandwidth for bidirectional transmission, Metz said.

Motorola has teamed with Turin Networks Inc. to offer cable operators a bi-directional Ethernet-based multiservice broadband-transport product.

"It's the next generation SONET [synchronous optical-network] core with Ethernet optimized interfaces and switching," said Metz, who hopes to handle two MSO trials by year-end.

At present, MSOs either link points on an OCM-3 network together in a daisy chain, or add low-speed Ethernet links to handle in-system backhauls of VOD traffic. But those solutions don't offer bandwidth management, Metz said.

The new product would allow MSOs to "stream while moving to a distributed network," Metz said. MSOs can use the bidirectional product from one master server to eight hub servers, "From eight servers to hubs and homes, they can use the GTS simplex," he said.

S-A is also working in the GigE space, said vice president of marketing and network architectures Paul Connolly.

"The driver here is to lower the cost per bit and get higher capacity and scalability at a lower and lower cost," he said. "We have introduced two product platforms and both include ASI and GigE."

That's because there is still a large installed based of ASI systems. (S-A ships ASI QAMS at present, but plans to introduce GigE QAMs soon.)

S-A's Prisma GBE product "takes GigE in at the server side, produces GigE out, and can convert the signal to ASI if necessary," Connolly said. "On the interface devices, we take three GigE signals and put them into 2.4 GigE signal, framing them using SONET.

"It's dense wave-division multiplexed into as many as 40 wavelengths," he said. "Every wavelength has three GigE signals. It's three times the efficiency vs. mapping a GigE into one wavelength."

That gives MSOs more flexibility.

"They want to be able to switch traffic in and out. We built a layer 2 switching interface into our product." That product has come from the S-A's BarcoNet product line.

S-A's second family of products is the Prisma IP resilient packet ring product, which would allow for both data and video transport, Connolly said.

"It has much broader capability," he said. "It can handle MPEG [Moving Picture Expert Group] and IP transport."

Some MSOs plan to trial the product, which is at 2.5 gigabit speed but can ramp to 80 gigabits per wavelength, Connolly said. Cox Communications Inc. has bought the product to carry T-1 telephone-type traffic in Lafayette, La., he said.