Digging Deeper Into SFP Transceivers
A compact, hot-pluggable optical transceiver, the Small Form-Factor pluggable (SFP) transceiver is used in optical communications for both 10g transceiver module telecommunication and data communications applications. SFP is the interface between a network device mother board and a fiber optic or copper cable network cable.
The SFP transceiver is able to support Gigabit Ethernet, Fiber Channel, SONET, and a number of other communications standards. FYI, in the near future, SFP is going to expand to SFP+. At that time, data rate at 10 Gbit/s will be achievable, including 8 Gigabit Fiber Channel. Compared to Xenpac or XFP type of modules which have all of their circuitry inside, an SFP+ module leaves some of its circuitry to be implemented on the host board.
The SFP transceiver has an immense variation available, each with different transmitter or receivers. This allows the user to configure and customize the transceiver to get the proper optical reach with either a multi-node fiber or single-node fiber type. Additionally, the optical SFP module comes in four categories – SX, which is 850nm, LX, which is 1310nm, ZX, which is 1550nm and DWDM. All of them have an interface of a copper cable which permits a mother board to communicate via USTP (unshielded twisted-pair) network cable. There also exist a CWDM and single-node bi-directional fiber optic cables which are 1310/1490nm upstream and downstream.
Practically available, the SFP transceiver has the capability transfer rates of up to 4.25 Gbit/s. XFP, a form factor which is virtually identical to the SFP type, increases this amount by nearly three times, at 10 Gbit/s. The SFP transceiver is specified and made compatible via a multi-source agreement (MSA) between manufacturers, so that different users who may use equipment from different manufacturers and providers can work effectively and smoothly without worrying about errors and inconveniences.
The GBIC interface is the precursor to the SFP, hence it’s nicknamed as mini-GBIC. However, the SFP allows greater port density (number of transceivers per inch along the edge of a mother board) than the GBIC. There also exist the identical Small Form-Factor (SFF) transceiver which is about similar size as the SFP. Rather than plugged into an edge-card socket, it is directly attached to the mother board as a pin through-hole device.
Digital optical monitoring (DOM) or digital diagnostics monitoring (DDM) functions are supported by the modern optical SFP transceiver according to the industry specifications of the SFF-8472 MSA. The user has the ability to constantly monitor real-time parameters of the SFP, such as optical input/outp power, supply voltage and laser bias current because of this feature.