MMF is also the common abbreviation for multi-mode fiber - a variant of fiber optic used in data and voice networking.

MMF is the working-man's fibre - cheap (well, cheapER then single-mode fiber or SMF), (relatively) easy to produce and quite reliable. It runs at a wavelength of 62.5/125um (that's nanometers I believe) and has a variety of advantages.

MMF can run individual segments of both Ethernet and Fast Ethernet at lengths of up to 500m (plain old meters) - however is designated as 10BaseF and 100BaseFX respectively to show its Fiber nature rather than Twisted Pair origins. While this helps overcome the 100m limit distance problems of Twisted Pair, it does raise the cost of installation.

MMF is also full duplex - each fiber in the MMF pair is one-way, leading to a few cabling misunderstandings as you get the pairs the wrong way (RX-RX, TX-TX). As a result you can get good speed benefits in network interface cards that can handle full duplex without resorting to additional infrastructure.

Being optically based, you can run MMF with impunity in area with high electromagnetic noise. Great if you are looking to operate in ungrounded, electrically noisy environments.

MMF can be readily converted for data transmission - 10BaseF to 10BaseT and 100BaseFX to 100BaseTX media converters are readily available. Allied Telesyn make good quality, reliable media converters (the AT-MC12/13 and AT-MC101XL respectively) with the full variety of termination.

MMF is terminated using the standards:

  • ST - each fiber strand has a rounded, bayonet-style connector similar to BNC (Coax) cabling, but much smaller and very secure (no trip disconnections!)
  • SC - each fiber strand has a square connector for simple connection - held only by insertions friction - more popular nowadays than ST
  • MTRJ - a relatively new phenomenon, it is a compact all-in-one connector, the two fibers are fused in to one single plug held with a built-in clip. Great economy on space, but totally incompatible with other termination points (you CAN get ST-SC in-line converters)
Additionally, MMF can be used for optical sources like security cameras, your MiniDisc or high-quality surround sound without your other speaker wires interfering ;-) and realtively cheap optical analogue signal processors (FAR cheaper than digital/data signal processors).

Overall MMF has lots of advantages and few disadvantages - mainly price and being fragile, as any fiber is. So remember - look out for your orange friend - the unofficial standard cladding for MMF is a bright, cheery orange!