SFP - Small form-factor pluggable transceiver

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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.SFP transceivers are designed to support SONET, Gigabit Ethernet, Fibre Channel, and other communications standards. Due to its smaller size, SFP obsoletes the formerly ubiquitous gigabit interface converter (GBIC); the SFP is sometimes referred to as a Mini-GBIC although no device with this name has ever been defined in the MSAs.

Contents

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:

SFP+

The enhanced small form-factor pluggable (SFP+) is an enhanced version of the SFP that supports data rates up to 10 Gbit/s. The SFP+ specification was first published on May 9, 2006, and version 4.1 published on July 6, 2009.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.

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.

Consideration has to be given to whether the module is linear or limiting. Linear SFP+ modules are most appropriate for 10GBASE-LRM; otherwise, limiting modules are preferred.

SFP Fiber Optic Transceiver

The small form-factor pluggable (SFP) Fiber Optic Transceiver supports data rates up to 10 Gbit/s. SFP Fiber Optic Transceivers are available with a variety of transmitter and receiver types.

Compatiblity

It is possible to design an SFP+ slot that can accept a standard SFP module.

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 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) 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 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 only enable the vendor's own modules.

Signals

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

SFP pin-out
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)
16 VccT Transmitter power (3.3 v)
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 XFP
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 digital diagnostics monitoring (DDM) functions according to the industry-standard SFF-8472. 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.

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

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