40G Ethernet Migration Strategy Over Multimode Fiber

With the increasing network bandwidth to meet the global IP traffic demand, there will be a need to upgrade to 40G Ethernet links for switch to server and storage area network connections in data centers. And the biggest market for 40G Ethernet (40 GbE) is in data centers for interconnection links with servers and storage area networks. So this article will talk about migration strategy for 40G Ethernet over multimode fiber.

40G Ethernet Standard

IEEE published the IEEE 802.3ba standard for 40 Gigabit Ethernet in June 2010. The following table illustrates the capabilities of different grades of multimode fibers (OM1, OM2, OM3 and OM4) to support different Ethernet applications. Only the laser optimized multimode fibers OM3 and OM4 are capable of supporting 40G Ethernet. The cabling requirements for 40GBASE-SR4 will be focused and guidance on an effective migration strategy to transition form 10G to 40G will be provided.

40G Ethernet Standard

40G Ethernet Over Multimode Fiber

40G Ethernet over multimode fiber uses parallel optics at 10Gb/s per lane. One lane uses 1 fiber for each direction of transmission. 40G requires 8 fibers. The concept of parallel transmission at 10 Gigabits per lane is illustrated below. The minimum performance that is needed to support 40G over multimode fiber is OM3 fiber for a distance of 100 meters. Cabling with OM4 fiber provides the capability to extend the reach up to 150 meters.


Media Dependent Interface (MDI)

The MDI is the physical interface that connects the cabling media to the network equipment. For multimode fiber, the media dependent interface is the MPO adapter that meets the dimensional specifications of IEC 61754-7 interface 7-3. The corresponding MPO female plug on the optical fiber cable uses a flat interface that meets the dimensional specifications. 40 GbE uses the MPO connector interface at the MDI and uses a 12 position MPO connector interface that aligns 12 fibers in a single row. Four transmit fibers are used on one side and four receive fibers are used on the opposite side of the MPO connector, for a total of eight fibers. The middle four fiber positions are not used.

Migration Path From 10G to 40G for Multimode Fiber

Migrating from 10G (that uses two fibers in either a SC Duplex or a LC Duplex connector) to 40G will require a lot more fibers and a different type of connector. The way that optical fiber cabling is deployed for 10G can facilitate an easier migration path to 40G. An effective migration strategy needs to provide a smooth transition to the higher Ethernet speeds with minimum disruption and without wholesale replacement of existing cabling and connectivity components.

Optical fiber cabling is commonly deployed for backbone cabling in data centers for switch to switch connections and also for horizontal cabling for switch to server and storage area network connections. The use of pre-terminated optical fiber cabling can facilitate the migration path to 40G. A pre-terminated cable assembly containing 24 OM4 multimode fibers with two 12-fiber MPO connectors at both ends plugs into the back of a breakout cassette that splits the 24 fibers into 12 LC duplex connectors at the front of the cassette. It is necessary to provide some 40G connections, either as a replacement of or as an addition to the existing 10G connections.

The first case: if upgrading from 10G to 40G, one or more of the LC duplex cassette/cassettes can be replaced with 12 MPO adapters. The MPO adapters are designed to fit in the same opening as the cassettes. Fiberstore offers a high-density 18 MPO adapter with the same overall physical dimensions as 12 MPO adapter. This is an upgrade path from 10G to 40G that does not require any additional space and reuses the same patch panels. For instance, the 12 LC duplex cassettes could be replaced with either a 12 MPO or 18 MPO adapters as needed.

The second case: if it is required to add some 40G connections while retaining the 10G connections, a high-density cassette containing 18 LC duplex connections in the same space as a 12 LC duplex cassette would be used. Three of the 12 duplex cassettes can be replaced with three 18 LC Duplex cassettes, thus maintaining the 48 10G connections while freeing space for either a 12 MPO or 18 MPO adapter providing up to 18 additional 40G connections. The requisite number of additional fiber cable assemblies in multiples of 12 fibers are provided as needed.


Pre-terminated optical fiber cabling provides a seamless migration path to 40 Gigabit Ethernet using the same infrastructure by adding pre-terminated trunk cable assemblies and MPO adapter frames as needed. The use of Fiberstore’s pre-terminated cabling facilitates the migration to 40G Ethernet from 10G Ethernet networks today.