Things to Know About 10GBASE-LRM

As 10 Gigabit Ethernet broadly rolls out and increasing numbers of enterprises begin the process of evaluating network upgrades, numerous physical-layer interconnects are available to address 10Gbit/s data transmission. These include 10GBASE-LX4, CX4, SR, LR, and ER, as well as emerging 10GBASE-T (802.3an), 10GBASE-KX4 (802.3ap), and 10GBASE-LRM (802.3aq). With all of these options, it can be a difficult process to sort through the requirements of a specific implementation. In this article, 10GBASE-LRM standard, one option that meet existing installed multi-mode fiber cabling plant in building backbone, switch-to-switch, data center, and other enterprise-related environments, will be introduced.

What Is 10GBASE-LRM?

Multi-mode fiber dominates the installed base of fiber plant for data communications. Older multi-mode fibers installed in the early 1990s exhibit large amounts of modal dispersion, making for a challenging transmission channel, particularly at 10G data rates. For vertical-riser applications in building backbones, transmission distances of up to 300 m are required, and pulling new fiber is not a cost-effective option. The requirements of the vertical-riser application must be addressed to make 10G optical deployment a viable alternative in the enterprise backbone. The current standards-based design for the vertical-riser link is known as 10GBASE-LX4. LX4 uses a CWDM approach using four wavelength-specific transmitters near 1300 nm, a CWDM multiplexer and demultiplexer, and four receivers. The disadvantages of this architecture are significant challenges in cost, size reduction, and manufacturability. As a result of these disadvantages, vendors have developed an alternative approach called 10GBASE-LRM. LRM stands for long reach multi-mode. 10GBASE-LRM, as the replacement to LX4, will reach up to 220m over standard multi-mode fiber, but without the complexity of the LX4 optics. The following is a picture of 10GBASE-LRM transceiver modules.

How Does 10GBASE-LRM Work?

LRM uses a 10G serial approach with a single 1310nm transmitter and a receiver with an adaptive electronic equalizer IC (integrated circuit) in the receive chain. This adaptive equalization technology, known as electronic dispersion compensation (EDC), working on a way to provide a long-distance multi-mode solution that operates with a single wavelength, is used to compensate for the differential modal dispersion (DMD) present in legacy fiber channels. EDC is a form of signal processing that removes interference from the received optical signal and recovers an open "eye" from a closed eye. The EDC function is one that can be integrated into the serializer, and perhaps even done in complementary metal-oxide-semiconductor transistor (CMOS) over time, which suggests that it can achieve a very low cost and fit into very small form factors. 10GBASE-LRM can provide a long distance solution based on multi-mode fiber and operates with a single wavelength.

10GBASE-LRM Transceiver Modules

LRM modules use a single higher-speed laser operating at 10.310Gbit/s rather than 3.125Gbit/s. This creates a simpler optical path, but requires more expensive components. The LRM laser can either be a distributed-feedback (DFB) laser, a vertical-cavity surface-emitting laser (VCSEL), or a Fabry-Perot (FP) laser. Both DFBs and VCSELs provide a very clean, single-wavelength output, which minimizes signal degradation due to spectral effects. On the other hand, an FP laser source produces a range of different wavelengths. Each of these wavelengths travels through the fiber at slightly different speeds, creating additional jitter that must be recovered by the EDC circuit at the receiver. While small, this added jitter could compromise operation on some fibers.

The EDC chips used in the LRM modules are also very complex and require a highly linear transimpedance amplifier (TIA) and a high-speed photodiode with a large surface area capable of capturing all of the optical modes at the output of a fiber. Thus, LRM offers the advantage of fewer components, yet the increased performance requirements for each individual element may be a substantial barrier to the overall module cost savings speculated by LRM advocates.

Fiberstore offers you a compatible 10GBASE-LRM transceiver solution at a fraction of the original cost and a 5-year warranty. These products are manufactured per precise OEM specifications and with high quality. For example, SFP+ transceiver JD093B branded by HP, and SFP+ transceiver EX-SFP-10GE-LRM branded by Juniper, all these 10GBASE-LRM transceivers are with high quality to meet your 10 Gigabit fiber cabling needs.