Tech Trends: Small Form Factor – Pluggable

Security is finally getting on board with SFP technology


Those who have been in the industry awhile may remember the early days of fiber optic transceivers, where, in addition to specifying the function that was needed (for example, RS-232 to fiber optic), you had to define wavelength, number of fibers, connector type, and possibly optical budget. In addition, there might have been the choice of end point, repeater, or multi-port star or hub. All of this made for a dizzying array of part numbers and complicated the specification, ordering, and stocking of transceiver products.

There’s actually technology that’s been around the datacom and telecomm industry for nearly 15 years that addresses this dilemma. Because the security industry is squarely in the middle of a shift to IT equipment and protocols, we’re seeing switches and routers that reflect this. I’m referring to pluggable transceiver modules.

The Gigabit Interface Converter (GBIC) was introduced in 1999, originally specified for fiber channel applications. It allowed a small module to plug into transmission equipment using fiber channel or Gigabit Ethernet. Shortly thereafter, a mini GBIC called a SFP (small form factor pluggable) transceiver was introduced. The SFP has a slightly smaller footprint than the GBIC and is used for data rates up to four Gb/s. It has various fiber options, including Dense Wavelength Division Multiplexing (DWDM), and it has an RJ-45 copper option. Fiber interfaces can be multi-mode or single mode, implement different fiber optic Ethernet standards (relating to wavelength, distance, and data rate), and support different fiber optic connectors, although LC is the most common.

Beginning around 2000, a number of industry players including Agilent, Fujikura, IBM, Lucent, Molex, and Tyco Electronics agreed to the Small Form-factor Pluggable (SFP) Transceiver MultiSource Agreement (MSA) “to establish internationally compatible sources of a pluggable fiber optic transceiver module in support of standards for fiber optic systems. Each party expects that the establishment of compatible sources for an interchangeable transceiver module will allow the entire fiber optic marketplace to grow more rapidly. This enhanced marketplace growth, customer choice, and vigorous competition are the express purposes of this Agreement.” The MSA defined both physical and electrical parameters for devices that would plug into single or multiple unit receptacles (cages) and be hot swappable. Some optical SFP transceivers now support digital diagnostics monitoring (DDM) functions, also known as digital optical monitoring (DOM), giving users the ability to monitor real-time parameters such as optical output power, optical input power, and temperature.

But let’s focus on security. The first way this technology impacts the industry is fairly obvious. Purchase, for example, a managed switch with SFP capability and add SFP modules as you need them to suit the media and distance that is present. If there are spare receptacles, there’s future expandability. Note that some ports may be designated as either/or, where you choose to use an existing RJ-45 jack or populate an SFP on the same port number. The beauty is that you pay only for the optics you need at the time while, on the supply side, manufacturers and resellers can simplify their inventory.

A word of caution relates to manufacturer warranty and support. While researching Cisco’s policy, I found this: “When a customer reports a product fault or defect and Cisco believes the fault or defect can be traced to the use of third-party memory products, cables, GBIC’s, filters, or other non-Cisco components by a customer or reseller, then, at Cisco’s discretion, Cisco may withhold support under warranty or a Cisco support program...” Also, on-line postings suggest that third party SFP’s may not work out of the box and may require a Cisco IOS command such as “service unsupported-transceiver” to successfully operate. It’s always best to check.

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