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Bringing Intelligence to the Optical Network

Technologists describe the network as being divided into several layers. Layer one is the basic transport layer in which optical networking equipment including SONET and WDM exists. In layer 2 are devices such as ATM and frame relay switches. Layer 3 consists of IP routers. Collapsing those layers could make the network simpler to operate and create fewer points of failure. It could also enable a network operator to switch lambdas (i.e. optical wavelengths) in layer 1 based on the smarts of layer 3, which means potentially much faster bandwidth provisioning schedules.

While the automatic protection switching feature of SONET provides carriers with the network resiliency they need, it lacks other capabilities they would like, explains Vinay Rathore, director of product marketing and business development for the carrier internetworking business at Alcatel N.V. (www.alcatel.com). Meanwhile, DWDM, which divides a fiber strand into multiple wavelengths to multiply the capacity of fiber, lacks any intelligence. Router networks provide significant intelligence, but are best effort and require tens of seconds rather than the tens of milliseconds in optical networks for restoration in the event of an outage. So to obtain the best of both worlds between optical and router networks, one must converge the two technologies into a single optical IP core network, he says.

"The idea between IP and optics is the unified control plane [UCP] where rather than reinventing the wheel, one plane can control both, so when you're doing traffic engineering it gives you better visibility into the network," adds Vijay Parikh, vice president and general manager of the IP PoP systems business unit at Cisco Systems Inc. (www.cisco.com). "UCP is the No. 1 activity we are focused on."

However, according to Ram Krishnan, director of internetworking for the IP core routing group at Lucent Technologies Inc. (www.lucent.com), there are two schools of thought on how to do it. Cisco, he says, believes that optical devices should be devoid of any intelligence in this new model, but Lucent believes there should be intelligence resident at the optical level as well as at the router layer.

Although there may be differences of opinion as to the extent to which intelligence should be infused in the optical network, both routers and optics will play a key role in this new intelligent optical core. Most services are IP-based, and routers see at the IP level while optical equipment does not, explains Pete Chadwick, vice president of product management at router vendor Avici Systems Inc. (www.avici.com). "IP sees the service, so it sees congestion," he says. "You need the two of them because intelligent optics lets you manipulate bandwidth, but routers can tell you how bandwidth is allocated and used."

Routers are very familiar with blocking, which happens if there's too much traffic; layer 1 generally doesn't know that, adds Arun Jain, director of marketing for IP infrastructure at Nortel Networks (www.nortel.com). "But what if the signaling of layer 3 can talk to layer 1?" he says, adding that Nortel next year plans to add a packet core router to its Optera optical product line.

To put it in more concrete terms, let's say a website runs an advertisement during the Superbowl instructing viewers to visit the site. The site could get so many visitors it would crash as a result. But in this new world that would marry routers and optics, there would be enough intelligence in the optical and router layers of the network that they would detect the heavy load of incoming traffic and offload some of it to another site within the network.

But that kind of real-time core network bandwidth provisioning simply isn't possible today. In fact, provisioning a high-speed SONET link typically takes somewhere in the neighborhood of six months, explains Scott Larson, director of product marketing for strategic programs at Sycamore Networks Inc. (www.sycamorenet.com). "The patch panel is very manually intensive," he says.

"Sycamore has a range of transport, management and switching products. The heart of that is software that enables automatic point and click provisioning to allow [bandwidth to be provisioned in] six days or minutes vs. six months," he says.

Adds Nortel's Jain, bandwidth today is sold in increments of years. That's because it takes weeks or longer to engineer and provision it. "This layer integration will allow for bandwidth on demand," says Jain.

While there seems to be general consensus among both carriers and equipment suppliers that getting the optical and switch/router layers to communicate is the right road for the industry to take, still up in the air is exactly what language these boxes should speak to allow for interoperability and other logistical details. But the Optical Internetworking Forum (www.oiforum.com) and the Optical Domain Service Interconnect group (www.odsi.coalition.com) are working the issue.

Router king Cisco established the OIF in 1998. The group is comprised of about 225 members worldwide including carriers, ISPs, and systems and components manufacturers. Its charge is to enhance interoperability between data networking equipment including IP routers, ATM and Ethernet switches, and optical equipment including WDM products and new optical switches, says Joe Berthold, vice president of network architecture and standards at Ciena Corp. (www.ciena.com) and chairman of the OIF's technical committee.

The major thrust for OIF this year is a signaling specification--a user network interface--to allow a piece of data network equipment to request and receive a connection across the optical network. That also happens to be the thrust of the ODSI, which intelligent optical networking vendor Sycamore founded this January specifically to address the signaling issue. Sycamore's Larson describes ODSI as an informal group focused on defining the optical user to network interface and says at the time it was formed OIF hadn't yet addressed this interface. "We're a short-lived endeavor and a catalyst," says Larson.

Berthold says OIF wants to be as compatible as possible with the Internet and the Internet Engineering Task Force (www.ietf.org), which is working on multiprotocol label switching (MPLS). Within MPLS there are routing and signaling protocols, and within signaling there are several signaling protocols. Resource reservation protocol (RSVP) and line appearance on a digital trunk (LDT) are two signaling options within MPLS, but both are rather complicated, Berthold says. The OIF and ODSI, which Berthold says is pushing using TCP signaling, were considering asking the IETF to find a scaled down version of RSVP, he says. OIF was expected to pick a signaling protocol in August and expects to complete a final draft on the issue by the end of the year.

David Skirmont, systems architect at large-scale router vendor Pluris Inc. (www.pluris.com), says that today when a packet goes through the network you don't know what path it took. "MPLS lets you set up paths end to end through your system and do QoS as a result. MPLS is the same idea as optical switches--you can establish paths and signal what path a packet takes by what wavelength it is." He adds that MPLS is a hot area in the IETF and could "displace the ODSI effort."

Other issues on the drawing board at OIF are how to create standards for network self-discovery. Self-discovery would enable network technicians to plug equipment into the network and that equipment would automatically register itself to the network so there's a record of what boxes are on the network and the status of ports on each box. For example, a 10 gigabit router interface could have one big fat pipe going to it or could be channelized into 16 interfaces at 622mbps or 4 interfaces at 2.5gbps. Seeing what ports are available on the router would enable the optical network to reroute traffic to different parts or channels on that box, Berthold explains.

Also being discussed is how to handle basic network management. Such issues include what restoration capabilities to support.

Another key initiative at OIF is creating a spec for a very short reach (VSR) interface between routers and optical equipment. The goal here is to make it more affordable for 10 gigabit routers to interconnect with optical equipment.

"The VSR proposal includes techniques to use lower cost, lower power optics to connect transmission and network equipment. Today, routers and SONET equipment are in the same COs but normally use high power and precise clocking [which they'd need for long distances]," explains Skirmont of Pluris.

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