This is a good guide for running 40G on existing MMF fiber.
The use of parallel optics in 40GbE multimode fiber cabling (MMF cabling) require more fiber strands than the 10GbE infrastructures. Thus, data center will require a cabling upgrade to meet the requirement of migration. In this case, cost is a big factor. To help user solve the fiber cost issue, many vendors developed a new transceiver alternative that allow zero-cost fiber migration by reusing the current 10Gbps multimode fiber-optic cabling plant for 40Gbps connectivity. This post will introduce three mainstream transceiver options for running 40GbE over duplex multimode fiber cable with LC connectors.Option 1: Cisco QSFP 40G BiDi Transceiver (QSFP-40G-SR-BD)
The Cisco QSFP BiDi transceiver can transmit full-duplex 40Gbps traffic over one duplex OM3 or OM4 MMF cable with LC connector. It provides the capability to reuse 10Gbps fiber infrastructure, enabling data center operators to upgrade to 40Gbps connectivity without making any changes to the previous 10GbE infrastructures.
The working principle of Cisco QSFP BiDi transceiver is that it uses two 20Gbps channels, each transmitted and received simultaneously over two wavelengths on a single MMF strand, as shown in the following.
Concept of QSFP BiDi transceiver
Cisco QSFP BiDi transceiver can be supported in most Cisco switching and routing products that support 40GbE interfaces. The connection distance can reach up to 100 meters over OM3 MMF or 150 meters over OM4 MMF, which is the same as 40GBASE-SR4 QSFP+.
Note: The other version of Cisco QSFP BiDi transceiver (QSFP-40G-BD-RX) is almost the same with the QSFP-40G-SR-BD, but with link monitor hardware, such as the Cisco Nexus® Data Broker.
Option 2: Juniper 40Gbps QSFP+ LX4 (JNP-QSFP-40G-LX4)
Juniper 40Gbps QSFP+ LX4 module uses the same infrastructure as 10GbE. The LX4 technology represents a new way to deploy 40GbE that meets all of the performance criteria of today’s data centers by providing 40GbE on two MMF strands with duplex LC connectors. Thus, users can simply replace existing 10GbE transceiver modules with 40GbE LX4 modules without expensive 40GbE migration cassettes and additional fiber infrastructure.
As the following picture shown, QSFP+ LX4 transceiver uses four 10Gbps channels, each transmitted and received simultaneously over four wavelengths on a single MMF strand. Similar with the 40GBASE-SR4 modules, it can also support transmission distance up to 100 meters over OM3 MMF or 150 meters over OM4 MMF cable. Juniper 40Gbps QSFP+ LX4 can be supported in many Juniper devices that support 40GbE interface, such as QFX3000 QFabric system, QFX5100 switches, and so on.
Concept of QSFP+ LX4 transceiver
Note: The Juniper 40Gbps QSFP+ LX4 also support to run over single-mode fiber (SMF: OS1) and reach up to 2 kilometers.
Option 3: Arista Networks QSFP-40G-UNIV Transceiver
The Arista networks QSFP-40G-UNIV is a 40GbE QSFP+ transceiver with a duplex LC connector that can be used with both MMF and SMF. Its working principle is similar with the Juniper LX4 mentioned above, having 4 channels of 10G multiplexed inside the module to transmit and receive an aggregate 40Gbps signal over 2 strands of fiber. UNIV is short for the word “universal” because of its ability to operate with both MMF and SMF without the need for any software/hardware changes to the module or any additional hardware in the network. The Arista networks QSFP-40G-UNIV can operates on OM3 or OM4 MMF for distance up to 100 meters or SMF (OS1) for distance up to 500 meters. It is noted that this QSFP module can interoperate with Cisco and other vendors standards based 40GbE LR4 optics.