Long Reach Multimode (LRM)

The IEEE 802.3 standard will soon specify a new physical layer interface, 802.3aq, which will incorporate a new and innovative method for real-world testing. The 10 Base LRM standard will define a physical layer specification for low cost 10GE communication over 62.5µm (FDDI-grade) and 50.5µm multimode fiber links.

With enterprises increasingly seeking to install 10Gbps Ethernet links in the LAN backbone and in data centers for high-end server applications, switch manufacturers will require 10GbE interfaces in their next generation aggregation/edge equipment. Currently, multimode solutions offer a scant 100m coverage with conventional 850nm optics. The IEEE 802.3aq 10GBASE-LRM standard enables 10GbE transmission up to 300 meters on enterprise-class multi-mode fiber.

To enable transmission up to 300 meters, several barriers needed to be overcome. An IEEE taskforce performed a round-robin style study of over 300 types of multimode fiber. By analyzing parameters such as launch conditions, core utilizations and dispersion, the task force designed a model to mathematically characterize these effects. IC vendors collaborated to develop state of the art electronic filters to compensate for the diversity of measured affects. Two years of painstaking effort resulted in the test methodologies adopted for the 10 Base LRM performance standards. The result is a system designed to emulate single mode signaling over multimode fiber.

The IEEE standard specifies a comprehensive test created by splitting the communication signal into 4 paths, which are then recombined with different amounts of noise, delay and amplitude added to each path. This process effectively simulates the ISI created by multimode fiber. This ISI signal then modulates an optical source which is coupled to a “mode conditioning” patch chord to properly maintain transmission through multimode fiber.

Circadiant LRM Testing

The Circadiant Hydra MTS™ system will measure receiver sensitivity as defined by the comprehensive 10 base LRM specification. The system also will precisely measure the transmitter wavelength dispersion penalty (TWDP) of the test signal, using an externally supplied Digital Communications Analyzer (DCA). It will also have the capability to analyze the jitter tolerance and optical overload also called out for in the specification. The Circadiant Hydra MTS LRM is the most complete tool available in the industry to meet the 10 base LRM specification.

The 802.3aq LRM test requirements are likely to be even more challenging than the 803.3ae requirements themselves. Circadiant has always led the industry with stressed compliance testing and will continue its leadership role with comprehensive LRM compliance testing as well.

Learn more about Circadiant's 802.3aq LRM Testing Solution