Small form-factor pluggable transceiver

Front view of SFP module (LC connector). The blue extraction lever indicates operation with single-mode fiber.

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 jointly developed and supported by many network component vendors.^[1] SFP transceivers are designed to support SONET, Gigabit Ethernet, Fibre Channel, and other communications standards.

Types

SFP transceivers are available with a variety of 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:

• for multi-mode fiber, with black or beige^[1] extraction lever
  • SX - 850 nm, for a maximum of 550 m at 1.25 Gb/s (Gigabit Ethernet) or 150m at 4.25 Gb/s (Fibre Channel)^[2]
• for single-mode fiber, with blue^[1] extraction lever
  • LX - 1310 nm, for distances up to 10 km
  • BX - 1490 nm/1310 nm, Single Fiber Bi-Directional Gigabit SFP Transceivers, paired as BS-U and BS-D for Uplink and Downlink respectively, also for distances up to 10 km^[3][4]
  • 1550 nm 40 km (XD), 80 km (ZX), 120 km (EX or EZX)
  • CWDM and DWDM transceivers at various wavelengths achieving various maximum distances
• for copper twisted pair cabling
  • 1000base-T - these modules incorporate significant interface circuitry^[5] and can only be used for Gigabit Ethernet, as that is the interface they implement. They are not compatible with (or rather: do not have equivalents for) Fibre channel or SONET.

SFP transceivers are commercially available with capability for data rates up to 4.25 Gbit/s. An enhanced standard called SFP+ supports data rates up to 10.0 Gbit/s.

SFP+

The enhanced small form-factor pluggable (SFP+) is an enhanced version of the SFP. It supports data rates up to 10 Gbit/s. The SFP+ was first published on May 9, 2006, and version 4.1 published on July 6, 2009.^[6] SFP+ supports 8 Gbit/s Fibre Channel, 10 Gigabit Ethernet and Optical Transport Network standard OTU2. It is a popular industry format supported by many network component vendors.^[7]

In comparison to earlier XENPAK or XFP modules, SFP+ modules leave more circuitry to be implemented on the host board instead of inside the module.^[8]

Consideration has to be given to whether the module is linear or limiting. Linear SFP+ modules are appropriate for 10GBASE-LRM otherwise limiting modules are preferred.^[9]

Compatiblity

It is possible to design an SFP+ slot that can accept a standard SFP module.^[10][11]

Applications

COMBO6X card and attached 4SFPRO interface with SFP modules

Ethernet switch with empty SFP slots (lower left)

SFP sockets are found in Ethernet switches and network interface cards. Storage interface cards, also called HBA's and Fibre Channel storage switches is another use of these type of modules, supporting different speeds like 2Gb, 4Gb and 10Gb. Because the of their ability to provide a connection to different types of optical fiber, SFP provides such equipment with enhanced flexibility.

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 cm 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]}

However, as a practical matter, some networking equipment manufacturers engage in vendor lock-in practices whereby they deliberately break compatibility with "generic" SFPs by adding a check in the device's firmware that will only enable the vendor's own modules.^[12]

Signals

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

SFP pin-out

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

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

SFP dimensions are:^[13]

Height: 8.5 mm (0.33 inches)

Width: 13.4 mm (0.53 inches)

Depth: 56.5 mm (2.22 inches)

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 1010000X (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).

See also

• Optical interconnect
• Interconnect bottleneck
• Optical fiber cable
• Optical communication
• Parallel optical interface
• Serial digital interface

References

1. ^ ^{a b c} SFP MSA (MultiSource Agreement), ftp://ftp.seagate.com/sff/INF-8074.PDF 
2. ^ Agilestar/Finisar FTLF8524P2BNV specification, http://agilestar.com/p/datasheets/FTLF8524P2BNV-AS.pdf 
3. ^ Single Fiber Bidirectional SFP Transceiver, MRV, http://www.interlinkweb.com/systemics/assets/product_images/mrv/MRV-OP-SFPB_A4_HI-1.pdf, retrieved June 16, 2010 
4. ^ Gigabit Bidirectional SFPs, Yamasaki Optical Technology, http://yamasakiot.com/products/gigabit-sfp-bidirectional, retrieved June 16, 2010 
5. ^ VSC8211 media converter/physical layer specification, http://www.vitesse.com/products/download.php?fid=295&number=VSC8211 
6. ^ "SFF-8431 Specifications for Enhanced Small Form Factor Pluggable Module SFP+ Revision 4.1". July 6, 2009. ftp://ftp.seagate.com/sff/SFF-8431.PDF. Retrieved May 9, 2011. 
7. ^ "SFP+". Huihong Technologies. http://www.huihongfiber.com/sfp+.html. Retrieved 2011-01-27. 
8. ^ "10-Gigabit Ethernet camp eyes SFP+". LightWave. April 2006. http://www.lightwaveonline.com/about-us/lightwave-issue-archives/issue/10-gigabit-ethernet-camp-eyes-sfp-53428172.html. 
9. ^ Ryan Latchman and Bharat Tailor (January 22, 2008). "The road to SFP+: Examining module and system architectures". Lightwave. http://www.lightwaveonline.com/general/the-road-to-sfp-examining-module-and-system-architectures-54884162.html/. Retrieved July 26, 2011. 
10. ^ SFF-8432, Abstract, Page 1: "The mechanical dimensioning allows backwards compatibility between IPF modules plugged into most SFP cages which have been implemented to SFF-8074i. It is anticipated that when the application requires it, manufacturers will be able to supply cages that accept SFP style modules. In both cases the EMI leakage is expected to be similar to that when SFP modules and cages are mated."
11. ^ SFF-8431, Chapter 2 Low Speed Electrical and Power Specifications, 2.1 Introduction, Page 4: "The SFP+ low speed electrical interface has several enhancements over the classic SFP interface (INF-8074i), but the SFP+ host can be designed to also support most legacy SFP modules."
12. ^ John Gilmore. "Gigabit Ethernet fiber SFP slots and lock-in". http://www.toad.com/gnu/sysadmin/sfp-lockin.html. Retrieved Dec. 21, 2010. 
13. ^ (pdf) INF-8074i Specification for SFP (Small Formfactor Pluggable) Transceiver, SFF Committee, May 12, 2001, p. 6, ftp://ftp.seagate.com/sff/INF-8074.PDF