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Small form-factor pluggable transceiver
( Update Time : 9/2/2010 9:20:13 AM )

The small form-factor pluggable (SFP) or Mini-GBIC is a compact, hot-pluggable transceiver used for both telecommunication and data communications applications. It interfaces a network device mother board (for a switch, router, media converter or similar device) to a fiber optic or copper networking cable. It is a popular industry format supported by many network component vendors .SFP transceivers are designed to support SONET, Gigabit Ethernet, Fibre Channel, and other communications standards.

SFP types

SFP transceivers are available with a variety of different transmitter and receiver types, allowing users to select the appropriate transceiver for each link to provide the required optical reach over the available optical fiber type (e.g. multi-mode fiber or single-mode fiber). Optical SFP modules are commonly available in several different categories: 850 nm 550m MMF (SX), 1310 nm 10 km SMF (LX), 1550 nm [40 km (XD), 80 km (ZX), 120 km (EX or EZX)], and DWDM. SFP transceivers are also available with a copper cable interface, allowing a host device designed primarily for optical fiber communications to also communicate over unshielded twisted pair networking cable. There are also CWDM and single-fiber "bi-directional" (1310/1490 nm Upstream/Downstream) SFPs.

SFP transceivers are commercially available with capability for data rates up to 4.25 Gbit/s. The standard is expanding to SFP+ which will be able to support data rates up to 10.0 Gbit/s (that will include the data rates for 8 gigabit Fibre Channel, 10GbE, and OTU2). SFP+ module versions for optics as well as copper are being introduced. In comparison to Xenpak, X2 or XFP type of modules, SFP+ modules leave some of the circuitry to be implemented on the host board instead of inside the module.

SFP standardization

The SFP transceiver is specified by a multi-source agreement (MSA) between competing manufacturers. The SFP was designed after the GBIC interface, and allows greater port density (number of transceivers per inch along the edge of a mother board) than the GBIC, which is why SFP is also known as mini-GBIC. The related Small Form Factor transceiver is similar in size to the SFP, but is soldered to the host board as a pin through-hole device, rather than plugged into an edge-card socket.[citation needed]


Side view of SFP module (length is 6 cm).

The SFP transceiver contains a PCB that mates with the SFP electrical connector.

Pin Function Pin Function
20 VeeT 1 VeeT
19 TD- 2 TxFault
18 TD+ 3 TxDisable
17 VeeT 4 MOD-DEF(2)
16 VccT 5 MOD-DEF(1)
15 VccR 6 MOD-DEF(0)
14 VeeR 7 RateSelect
13 RD+ 8 LOS
12 RD- 9 VeeR
11 VeeR 10 VeeR

MOD-DEF 0,1,2 are the mode definition pins.

  • MOD-DEF 0 is grounded by the module to indicate that the module is present
  • MOD-DEF 1 is a clock SCL line for the I²C identification EEPROM
  • MOD-DEF 2 is a data SDA line for the I²C identification EEPROM

Mechanical dimensions

SFP dimensions are:

Height: 0.33 inches (8.5 mm)
Width: 0.53 inches (13.4 mm)
Depth: 2.22 inches (56.5 mm)

EEPROM information

The SFP MSA defines a 256-byte memory map in EEPROM describing the transceiver's capabilities, standard interfaces, manufacturer, and other information, which is accessible over I²C interface at the 8-bit address 10100000X (A0h).

Digital Diagnostics Monitoring

Modern optical SFP transceivers support digital diagnostics monitoring (DDM) functions according to the industry-standard SFF-8472. This feature is also known as digital optical monitoring (DOM). This feature gives the end user the ability to monitor real-time parameters of the SFP, such as optical output power, optical input power, temperature, laser bias current, and transceiver supply voltage.

The diagnostic monitoring controller is available as I²C device at address 1010001X (A2h).

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