Free Space Optical: Extending Optical Networks Where No Fiber Has Gone Before

Access to fiber is as critical to EtherLECS as access to copper pairs is to DLECs. Thus far, EtherLECs have enjoyed more cooperative business relationships with fiber suppliers than CLECs continue to experience with incumbents. But even in metropolitan areas perceived to be well served with fiber, the last several hundred meters-from the curb to the building-are an obstacle to service delivery for a considerable number of potential big-bandwidth customers. Those last few footsteps may as well be another mile. For if completing the first mile was too involved, too encumbered, and too expensive for incumbents and fiber speculators to justify in those sunny economic climates long past, it's certainly out of play for entrepreneurs in this economy.

EtherLECs seeking to maximize the precious capital they've acquired can look wishfully at the potential customer base that lies just beyond reach of their fiber partners. Or they can consider Free Space Optical.

Free Space Optical (in a nutshell)
If you understand how address records are beamed between Palm devices, you basically understand free space optical (FSO). FSO transmits invisible, eye-safe light beams from one "telescope" to another using low power infrared lasers in the teraHertz spectrum, where capacity can reasonably be expected to reach 10 Gbps. The light beam carries whatever optical transmission signal (layer 2 or MAC) and protocol framing a manufacturer chooses to market, typically SONET/ATM and 10/100/1000 Ethernet. Products targeted for access circuits typically support rates from T1 to 2.5 Gbps.

FSO requires no license, has repeatedly demonstrated a rapid time to deployment, and has a low cost per bit compared to fixed wireless or the already discounted alternative of laying new fiber. Over short distances, the savings from deploying FSO instead of a fixed wireless solution can be as much as 40%.

FSO has its detractors, largely from the vendor and service provider communities adversely affected when FSO is deployed. FSO technology is affected by building sway, which throws telescopes out of alignment. Manufacturers have mitigated this either by boosting power and widening the light beam or by incorporating an auto-tracking system. Temperature variations resulting from heated air rising from the ground may adversely affect signal amplitude. Careful positioning of telescopes often solves this problem. Weather interference, notably fog, is the most commonly cited drawback. The tiny water particles in fog act like mirrors and impair the light beam.

All these drawbacks are seemingly mitigated when you deploy FSO over short distances-those elusive several hundred to 500 meters of the first mile-and this is where opportunity shines for EtherLECs.

Forget the Roof, use a window
FSO technology that makes use of the 1550 nanometer wavelength operates at higher power than those systems operating in the 780-920 nanometer range. The 1550 nm FSO is more resilient to poor weather, entirely eye-safe, and most importantly, the light beamed between telescopes can penetrate through most windows. This may seem trivial, but it's not. Service providers can eliminate the need to negotiate rights to operate units on rooftops. Window-to-window FSO won't carry the additional cost associated with hardening units against bad weather. Physically securing window-to-window units within an office building is also a simpler task.

The most attractive aspect of deploying window-to-window FSO for a service provider is that it improves time to service. fSona claims that telescopes can be installed on tripods, indoors, in less than 30 minutes using its dynamic beam tracking and alignment system. More importantly, installs won't be delayed, blocked, or cancelled because the landlord won't cooperate or an incumbent won't make fiber available in time to meet the customer's needs. "When you lease fiber or copper, you are in the hands of other people who own your fate", says Heinz Willebrand, CTO of LightPointe, "EtherLECs don't have the capital to lay out new fiber, so they must leverage on existing infrastructure, and strategically deployed equipment like FSO gives a CLEC a cost effective infrastructure".

Deployment Alternatives
Individual subscribers who can't be reached by fiber may be served using a point-to-point system, from the customer's office to an EtherLECs facility, or perhaps to a building you can serve over fiber. A hub-and-spoke arrangement of customer sites beamed to a central (rooftop) FSO system can be aggregated over fiber from the hub site, thereby extending the reach of an existing EtherLEC fiber network. Some FSO equipment offers the ability to construct a mesh topology across an arbitrary number of buildings. These can be expanded over time to provide an entire serving area beyond the reach of fiber. When several buildings in the mesh are also served by fiber, the EtherLEC can provide considerable redundancy into its MAN network from the FSO mesh network.

Point-to-point FSO systems can be tuned to provide bandwidth according to customer needs. FSO mesh networks commonly offer the same bandwidth to all subscribers in the mesh. Consider whether you expect to complement fiber with FSO in a "one-off" manner or whether your ultimate goal is to extend the reach of your MAN service before you shop for FSO products.

A Full Spectrum of FSO Products
You can incorporate FSO products in a variety of ways, depending on your need and ambition for optical wireless. fSona and LightPointe, for example, offer layer one transmission products. These products effectively replace a fiber link with an optical link that is terminated on both ends by fiber interfaces connected to Ethernet switches. fSona's SONAbeam products currently operate at 155 Mbps. LightPointe FSO solutions provide anywhere from 20 Mbps to 1.25 Gbps, from 300 meters to 4 kilometers. Described by the company as protocol-, topology-, and architecture-agnostic, LightPointe's product can be quickly deployed to customers who can't be reached by fiber; moreover, a service provider can continue to use the same customer premises and metro network switching equipment and management.

Other companies offer integrated equipment solutions, complete FSO systems with companion switches. Optical Access sells a combination of optical switch and FSO equipment in both point to point and mesh topologies. The operating data rates of the TereScope and OmniSwitch FSO products scale from 1.5 Mbps to 1.25 Gbps. Optical Access also offers a combination infrared laser and radio frequency, where unlicensed RF in the 2.4 GHz ISM band is used as a back-up for FSO. Plaintree Systems' WaveBridge products bridge 10 Mbps and Fast Ethernet as well as ATM/OC-3 over FSO links. The bridged link can be interposed between customer and metro network switching equipment. AirFiber's OptiMesh rooftop system supports a mesh topology of 622 Mbps optical wireless links between companion ATM switching nodes.

Terabeam has deployed an FSO IP over Ethernet network with equipment it manufactures and competes with the likes of Yipes, Cogent, and other EtherLECs as a metro optical service provider and. Terabeam's indoor-outdoor transceivers are deployed in a hub-and-spoke configuration from customer to Terabeam hub sites, which are in turn interconnected by FSO or fiber. Terabeam claims its Fiberless Optics metro area network is one of the first to use MPLS for quality of service and traffic engineering.

FSO is not just an access play. EtherLECs can be more competitive in pricing access bandwidth if they can reduce the cost of their own metro network links as well as links to partner ISPs and national WANs. Where line of sight can be maintained, Gigabit and multi-gigabit FSO is sure to be less expensive than fiber leased from incumbents. FSO can also be offered as a redundant link to a customer's primary fiber.

Customer/Provider take on FSO
Building Technology Resources (BTR) delivers wireless broadband Internet to subscribers and in Dallas, College Station and Houston, Texas. Most of BTR's hops are licensed microwave, including a microwave OC3 SONET ring operating from some of the tallest buildings in the Dallas metro area and interconnects with local access loops for WorldCom, Qwest, and Global Crossing. BTR attracts subscribers who aren't reached by fiber or who are seeking access diversity for redundancy. BTR began deploying FSO because it had similar advantages to microwave and higher data rates. They are using LightPointe technology to complement and extend a SONET ring that included microwave and fiber. "By and large, we're very pleased with the cost, performance and reliability of FSO", reported Senior Network Engineer Richard Scott, "and we intend to continue to pursue it as a tool to meet short range/high bandwidth requirements."

Moving Forward with FSO
It's easy to dismiss line of sight technologies as having limited application. But Free Space Optical is anything but limited if it's used over short distances in metro areas to bridge the few hundred meters that separate an EtherLEC from a paying customer.

Metropolitan area landlords and city councils in Northern States connect high rise buildings with skyway bridges to provide relief from cold weather for tenants. In cities like Minneapolis, these have grown to form a network that benefits tenants and landlord-by extending the distance people can comfortably travel, they increase traffic flow across businesses. FSO offers EtherLECs the same opportunity.

You can take advantage of FSO, or you can leave a considerable potential customer base out in the cold.

David Piscitello is president of Core Competence, Inc., a network consulting firm and founder of The Internet Security Conference.