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What is a 10GBASE-LRM transceiver and why do I need it?

In the world of optical networks there are a lot of optical transceivers existing. They are a crucial part of the network as they are the ones in charge of the signal conversion and transmitting. There are some different form factors for 10 Gigabit transmissions, like SFP+, XFP, X2 and XENPAK - among them the LRM variant represents a special type of transceiver.

The 10GBASE-LRM transceiver is a Multi-mode transceiver designed and developed to be installed in a high-speed, enterprise environment. As data rates exploded, Multi-mode fibers and transceivers emerged as the optimal solution for short range transmissions. These transceivers are the perfect choice for building unified and scalable networks and interconnect buildings which are a few hundred meters apart.

With the latest trends in the networking world, network managers and architects are looking to expand their networks and upgrade them to 10 GB/s. This would mean better performance in the access layer, between the Datacenter and the customer, providing the customers with reliable, stable and super-fast connection. A significant part of the existing Gigabit connections were OM1 Multi-mode fibers which aren’t capable of delivering the 10 GB/s speed demand. With Multi-mode fibers the effect called “modal dispersion” is increasing as the speed increases. This means that the signal propagating along Multi-mode fibers is getting distorted as a consequence of the higher speed and longer distance. This issue drove the development of more robust and cost effective optical links which support 10 GB/s transmission speeds and which would help upgrade the existing Gigabit to 10 GB/s connections. The 10GBASE-LRM stands for Long Reach Multi-mode and is defined by the IEEE 802.3.aq standard. The LRM transceiver allows for an upgrade to 10 GB/s without making a change in the cable plant.

The main challenge in upgrading the existing enterprise Gigabit links to 10 GB/s links is the various modal bandwidth capabilities of various fiber optic cables. The modal bandwidth capability is the capability of the fiber to transmit a certain amount of data across a certain distance. Another key factor is the core size of the fiber. The core of the optical fiber is the glass center of the cable through which the light travels. When it comes to Multi-mode fibers there are generally two types of core diameter: 62.5µm and 50µm.

Since the end of 2005 there were two main optical transceivers existing on the market which supported the 10 GB/s links over Multi-mode fibers, 10GBASE-SR and 10GBASE-LX4. However in both cases the performance of the device and the reach capabilities depended on the type of the fiber used. This is why the new 10GBASE-LRM transceiver variant (figures 1 & 2) has been developed.

The need of a cost-effective optical transceiver which would have the same performance over any type of Multi-mode fiber drove the development of the 10GBASE-LRM transceiver variant. The key difference between the LRM transceiver and the earlier versions 10GBASE-SR and 10GBASE-LX4 is the longwave serial interface that includes an EDC chip on the receiving end, immediately after the receiver optical sub-assembly (ROSA). The EDC stands for Electronic Dispersion Compensation and this chip enables the adaptive equalization of the incoming modal dispersion. This eventually eliminates the dependency on optical cable types. The 10GBASE-LRM Transceiver can transmit data for up to 220 meters on any kind of Multi-mode fiber. The various characteristics are shown in the table below:

Multimode Fiber Typ1 ISO/IEC 11801: 2002 Fiber Typ Operating Range (Meter) Maximum Channel Insertion Loss (dB)
62.5µm 160/500   0.5 to 220 1.9
62.5 200/500 OM1 0.5 to 220 1.9
50 500/500 OM2 0.5 to 220 1.9
50 400/400   0.5 to 220 1.9
50 1500/500 OM3 0.5 to 220 1.9

The 10GBASE-LRM standard became the solution for upgrading existing Gigabit networks into 10 GB/s networks for distances up to 220 meters. The standard has been developed by the IEEE LRM Task Force which took a statistical approach for developing it. With the help of various tests and models they defined the transmitter and receiver parameters that guaranteed an error-free transmission for up to 220 meters.

In this solution IT managers and network architects can find a perfect solution for upgrading the existing Gigabit network architecture to 10 GB/s network architecture without making a change in the fiber plant. The 10GBASE-LRM Transceiver device has the capability to transmit 10 GB/s data over 220 meters distance on OM1 cables. The distance could be even greater with the introduction of OM3 and OM4 cables into the equation. This alone is enough to address a big portion of the enterprise upgrade requirements and to build a stable ground for even bigger future upgrades.