Mixing the Radio and the Light

By Eric Griffith

May 02, 2005

LightPointe's latest long-distance wireless is the first to combine free-space optics with radio frequency for connection backup.

LightPointe of San Diego is no stranger to long distance, outdoor, point-to-point connections, having specialized in the use of free-space optics (FSO) to put up connections where no physical line is possible or practical. It has fiber optic-like speeds of 1.25Gbps at full duplex. Perhaps best of all, light is license-free. FSO is certainly wireless, but wireless without the radio frequency technology that the term 'wireless' usually connotes. Until this week.

This week, the company announced at Interop its latest product, the FlightStrata 100 XA, which is its first to combine its optical wireless with a radio, specifically one using the license-free 5.8GHz spectrum as backup to the FSO connection.

Fast as FSO is, it's not perfect, as certain types of weather, fog or heavy snow in particular, can impact the connection. The radio backup will be able to kick in if the environment shuts down the connection, albeit at a slower speed than the 100Mbps FSO.

LightPointe expects a maximum speed of 72Mbps on the radio side, which is using a derivative of 802.11a modified by the company to boost the speed and "make it more point-to-point compatible," says Bob Preston, the company's senior vice president and CMO.

The company is patenting an architecture called DualPath which will make the "primary path the optical wireless, with all the benefits and throughput and speed at three nines," says Preston, referring to the 99.9 percent uptime of the optical connection. "This is backed up on the second path with seamless switching [to RF]... anything in the way of the primary connection will make it go automatically to the secondary path." The radio link will give the product uptime of "five nines" (99.999 percent), according to Preston. The modified 802.11a signal will go about five kilometers.

The DualPath switching will also prevent "flapping" back and forth between optical and radio on a day when fog could interfere intermittently. It forces the FlightStrata to stay with the wireless until the weather is stable. It knows to do so by monitoring the optical path connection for consistency.

For now, the DualPath switching system is run through a centrally managed unit meant for a LAN closet, but future generations of the product will get the switching technology embedded in the product's link-head. Preston says customers were split on where they wanted the technology housed. "Some want it inside for diagnostic purposes; half thought it was cool on the roof," he says. "We'll have both eventually."

Linking two buildings with the new FlightStrata will cost $35,000.

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