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) is a compact, hot-pluggable transceiver used for both telecommunication and data communications applications. The form factor and electrical interface are specified by a multi-source agreement (MSA). It interfaces a network device motherboard (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. Due to its smaller size, SFP obsolesces the formerly ubiquitous gigabit interface converter (GBIC); the SFP is sometimes referred to as a Mini-GBIC. In fact, no device with this name has ever been defined in the MSAs.

Although it is not mentioned in any official specification document, - the maximum data rate of the original SFP standard is 5 Gbit/s.[2]

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). SFP modules are commonly available in several different categories:

SFP+

The enhanced small form-factor pluggable (SFP+) is an enhanced version of the SFP that supports data rates up to 16 Gbit/s. The SFP+ specification was first published on May 9, 2006, and version 4.1 published on July 6, 2009.[11] 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.

10 Gbit/s SFP+ modules are exactly the same dimensions as regular SFPs, allowing equipment manufacturer to re-use existing physical designs for 24 and 48-port switches and modular linecards.

Although the SFP+ standard does not include mention of 16G Fibre Channel it can be used at this speed.[12] Besides the data rate, the big difference between 8G Fibre Channel and 16G Fibre Channel is the encoding method. 64b/66b encoding used for 16G is a more efficient encoding mechanism than 8b/10b used for 8G, and allows for the data rate to double without doubling the line rate. The result is the 14.025 Gbit/s line rate for 16G Fibre Channel.

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.[13] Through the use of an active electronic adapter, SFP+ modules may be used in older equipment with XENPAK ports.[14]

SFP+ modules can be described as 'limiting' or 'linear' types; this describes the functionality of the inbuilt electronics. Limiting SFP+ modules include a signal amplifier to re-shape the (degraded) received signal whereas linear ones do not. Linear modules are mainly used with the low bandwidth standards such as 10GBASE-LRM; otherwise, limiting modules are preferred.[15]

SFP+ also introduces Direct Attach for connecting two SFP+ ports without dedicated transceivers.

CSFP

The compact small form-factor pluggable (CSFP) is a version of SFP with the same mechanical form factor allowing two independent bidirectional channels per port. It is used primarily to increase port density and decrease fiber usage per port.

Compatibility

It is possible to design an SFP+ slot that can accept a standard SFP module. Some routing and Ethernet switch equipment allows for the use of a 10 Gbit/s transceiver at lower gigabit ethernet speed, such as with a 1 Gbit/s 1310 nm LX SFP.[16][17]

Applications

Ethernet switch with empty SFP slots (lower left)

SFP sockets are found in Ethernet switches, routers, firewalls and network interface cards. Storage interface cards, also called HBAs or Fibre Channel storage switches, also make use of these modules, supporting different speeds such as 2Gb, 4Gb, and 8Gb. Because of their low cost, low profile, and ability to provide a connection to different types of optical fiber, SFP provides such equipment with enhanced flexibility.

Standardization

The SFP transceiver is not standardized by any official standards body, but rather is specified by a multi-source agreement (MSA) among 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 through-hole device, rather than plugged into an edge-card socket.

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 enable only the vendor's own modules.[18] Third-party SFP manufacturers have introduced SFPs with "blank" programmable EEPROMs which may be reprogrammed to match any vendor ID.[19]

Signals

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

SFP pin-out[1]
Pin Name Function
1 VeeT Transmitter ground
2 TxFault Transmitter fault indication
3 TxDisable Optical output disabled when high
4 MOD-DEF(2) Data for serial ID interface
5 MOD-DEF(1) Clock for serial ID interface
6 MOD-DEF(0) Grounded by the module to indicate module presence
7 RateSelect Low selects reduced bandwidth
8 LOS When high, indicates received optical power below worst-case receiver sensitivity
9 VeeR Receiver ground
10 VeeR Receiver ground
11 VeeR Receiver ground
12 RD- Inverted received data
13 RD+ Received data
14 VeeR Receiver ground
15 VccR Receiver power (3.3 V, max. 300 mA)
16 VccT Transmitter power (3.3 V, max. 300 mA)
17 VeeT Transmitter ground
18 TD+ Transmit data
19 TD- Inverted transmit data
20 VeeT Transmitter ground

Mechanical dimensions

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

The physical dimensions of the SFP transceiver are slightly smaller than the later XFP transceiver.

Dimensions
SFP[20] XFP[21]
Height 8.5 mm (0.33 inches) 8.5 mm (0.33 inches)
Width 13.4 mm (0.53 inches) 18.35 mm (0.72 inches)
Depth 56.5 mm (2.22 inches) 78.0 mm (3.10 inches)

EEPROM information

The SFP MSA defines a 256-byte memory map into an EEPROM describing the transceiver's capabilities, standard interfaces, manufacturer, and other information, which is accessible over an I²C interface at the 8-bit address 1010000X (A0h).

Digital diagnostics monitoring

Modern optical SFP transceivers support standard digital diagnostics monitoring (DDM) functions.[22] This feature is also known as digital optical monitoring (DOM). Modules with this capability give the end user the ability to monitor parameters of the SFP, such as optical output power, optical input power, temperature, laser bias current, and transceiver supply voltage, in real time. This functionality is commonly implemented for monitoring on routers, switches and optical transport equipment via SNMP.

See also

References

Wikimedia Commons has media related to Small Form-factor Pluggable.
  1. 1 2 3 4 SFF Committee (2001-05-01), INF-8074i Specification for SFP (Small Formfactor Pluggable) Transceiver (PDF), retrieved 2012-08-12
  2. ↑ "FAQs for SFP+". The Siemon Company. 2010-08-20. Retrieved 2016-02-22.
  3. ↑ Agilestar/Finisar FTLF8524P2BNV specification (PDF)
  4. 1 2 3 1000BASE Gigabit Ethernet SFP Transceiver, Optcore, retrieved March 26, 2013
  5. ↑ Single Fiber Bidirectional SFP Transceiver (PDF), MRV, retrieved June 16, 2010
  6. ↑ Gigabit Bidirectional SFPs, Yamasaki Optical Technology, archived from the original on February 3, 2010, retrieved June 16, 2010
  7. ↑ "Single-fiber single-wavelength gigabit transceivers". Lightwave. Retrieved September 5, 2002.
  8. ↑ "The principle of Single Wavelength BiDi Transceiver". Gigalight. Archived from the original on May 3, 2015. Retrieved 2011.
  9. ↑ VSC8211 media converter/physical layer specification
  10. ↑ "Fiberstore: 100 Mbps SFPs".
  11. ↑ "SFF-8431 Specifications for Enhanced Small Form Factor Pluggable Module SFP+ Revision 4.1" (PDF). July 6, 2009. Retrieved May 9, 2011.
  12. ↑ Tektronix (November 2013). "Characterizing an SFP+ Transceiver at the 16G Fibre Channel Rate".
  13. ↑ "10-Gigabit Ethernet camp eyes SFP+". LightWave. April 2006.
  14. ↑ "SFP+ to XENPAK adapter".
  15. ↑ Ryan Latchman and Bharat Tailor (January 22, 2008). "The road to SFP+: Examining module and system architectures". Lightwave. Retrieved July 26, 2011.
  16. ↑ 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."
  17. ↑ 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."
  18. ↑ John Gilmore. "Gigabit Ethernet fiber SFP slots and lock-in". Retrieved December 21, 2010.
  19. ↑ "Reprogrammable SFPs".
  20. ↑ INF-8074i Specification for SFP (Small Formfactor Pluggable) Transceiver (pdf), SFF Committee, May 12, 2001, p. 6
  21. ↑ "INF-8077i: 10 Gigabit Small Form Factor Pluggable Module" (PDF). Small Form Factor Committee. August 31, 2005. Retrieved June 16, 2011.
  22. ↑ SFF-8472 (PDF), 21 November 2014, retrieved 2016-01-04
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