The small form-factor pluggable 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. It interfaces a network device motherboard 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 obsolesces the
formerly ubiquitous gigabit interface converter; the SFP is sometimes referred to as a Mini-GBIC
although no device with this name has ever been defined in the MSAs.
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.
Optical SFP modules are commonly available in several different categories:
for multi-mode fiber, with black or beige extraction lever
SX - 850 nm, for a maximum of 550 m at 1.25 Gbit/s or 150m at 4.25 Gbit/s
for single-mode fiber, with blue extraction lever
LX - 1310 nm, for distances up to 10 km EX - 1310 nm, for distances up to 40 km
ZX - 1550 nm, for distances up to 80 km, with green extraction lever
EZX - 1550 nm, for distances up to 120 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. Variations of bidirectional SFPs are also manufactured
which use 1550 nm in one direction. 1550 nm 40 km, 80 km, 120 km
SFSW – Single Fiber Single Wavelength transceivers, for bi-directional traffic on a single fiber.
Coupled with CWDM, these double the traffic density of fiber links.
CWDM and DWDM transceivers at various wavelengths achieving various maximum distances
for copper twisted pair cabling 1000BASE-T - these modules incorporate significant
interface circuitry and can only be used for Gigabit Ethernet, as that is the interface
they implement. They are not compatible with Fibre channel or SONET.
SFP+ The enhanced small form-factor pluggable 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+ also introduces Direct Attach for connecting
two SFP+ ports without dedicated transceivers. Compatibility
It is possible to design an SFP+ slot that can accept a standard SFP module.
Applications
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 among competing manufacturers. The SFP was designed
after the GBIC interface, and allows greater port density 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. Signals
The SFP transceiver contains a PCB that mates with the SFP electrical connector in the host
system. Mechanical dimensions
The physical dimensions of the SFP transceiver are slightly smaller than the later XFP transceiver.
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. Digital diagnostics monitoring
Modern optical SFP transceivers support digital diagnostics monitoring functions according
to the industry-standard SFF-8472. This feature is also known as digital optical monitoring.
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. See also
Interconnect bottleneck Optical communication
Optical fiber cable Optical interconnect
Parallel optical interface Q­ Small Form Factor Pluggable
Serial digital interface References