Gigabit Ethernet (GE) came into use in 1999 and has been gradually supplanting Fast Ethernet (FE) in wired local networks, due to the fact of being considerably faster. The transmission hardware used for connecting GE supported devices retains the compact Small Form-factor Pluggable (SFP) package. SFP is often called mini-GBIC (Gigabit Interface Converter). Because it is smaller size and has replaced GBIC modules in most 1Gb applications. The initial Gigabit Ethernet hardware standard was produced even one year earlier than its use. It is IEEE802.3z (1000BASE-X), which required optical fiber. Other Gigabit Ethernet standard SFP transceivers or non-standard but industry accepted Gigabit SFP transceivers were introduced successively in the past years.
Figure 1: Know SFP transceiver types.
SFP transceiver can be categorized into different versions under Gigabit Ethernet standards and industry-accepted standards, including 1000BASE-T, 1000BASE-TX, 1000BASE-SX, 1000BAS-LX, 1000BASE-LX10, 1000BASE-BX10, 1000BASE-LX/LH, 1000BASE-EX, and 1000BASE-ZX.
1000BASE-T (IEEE 802.3ab) transceiver is 1Gb copper SFP that transmits GE over twisted pairs. They make GE a desktop technology since users can use their existing copper cabling infrastructure. 1000BASE-TX (TIA/EIA-854) is similar copper SFP version but utilizes only two pairs of wires.
|Specified Data Rate||1000Mbps||1000Mbps|
|Medium||Twisted-pair cabling (Cat5 or higher level), using four bidirectional pairs, each pair supports a data rate of 250Mbps.||Twisted-pair cabling (Cat6 or higher level), using two unidirectional pairs (one pair transmit, one receive), each pair supports a data rate of 500Mbps.|
|Specified Distance||100 m (330 ft)||100 m (330 ft)|
|Symbol Rate||Four-dimensional five-level pulse amplitude modulation (4D-PAM5, 6dB coding).||Ten-Bit Interface (TBI, 8dB/10dB coding).|
Though 1000BASE-TX needs less wires for transmission, 1000BASE-T is still more widely. Possible reasons are that Cat6 cable is more expensive and 1000BASE-T has become cheaper. 1000BASE-T and 1000BASE-TX are generally not inter-operable in switches without a dual physical layer (PHY) since they use different coding approaches.
SFP transceivers that work over optical fiber consist of standard 1000BASE-SX, 1000BASE-LX and 1000BASE-LX10, and non-standard industry accepted 1000BASE-LX/LH, 1000BASE-LH, 1000BASE-EX and 1000BASE-ZX.
|SFP Version||Medium||Interface||Wavelength||Max. Distance||Notice|
|1000BASE-SX||MMF*||LC duplex||850 nm||FDDI (~ 220 m), OM1 (~ 275 m), OM2 (~ 550 m)|
|1000BASE-LX||MMF/SMF**||LC duplex||1310 nm||MMF (~ 550 m), SMF (~ 5 km)|
|1000BASE-LX10||SMF||LC duplex||1310 nm||~ 10 km|
|1000BASE-LX/LH||MMF/SMF||LC duplex||1300 nm/1310 nm||MMF (~ 550 m), SMF (~ 20 km)||Mode conditioning patch cable is required when used with MMF (only FDDI, OM1 and OM2, can not use with higher level MMF).|
|1000BASE-LH||SMF||LC duplex||1310 nm/1550 nm||~ 100 km|
|1000BASE-EX||SMF||LC duplex||1310 nm/1550 nm||~ 40 km|
|1000BASE-ZX||SMF||LC duplex||1550 nm||~ 70km|
*MMF = Multimode fiber. **SMF = Single-mode fiber.
The non-standard SFP transceiver versions are created by transceivers vendors to meet the requirements of Gigabit transmission of different applications. They are all compliant to Multi-Source Agreements (MSA) so as to ensure interoperability between different vendors equipment. For example, before the standard 1000BASE-LX10 was released, the non-standard versions 1000BASE-LX/LH and 1000BASE-LH have been in use as a proprietary extension.
For SFP transceivers that work over optical fiber, they can also be categorized into different types according to their fiber types. There are single-mode SFP and multimode SFP, as well as simplex SFP and duplex SFP.
Based on the types of optical fibers SFP transceivers work with, SFP transceivers are divided into single mode SFP that works with single-mode fiber and multimode SFP that works with multimode fiber. Let’s see what’s the major differences between them.
Figure 2: Color coding and fiber cable for single-mode SFP and multimode SFP.
|Specifications||Multimode SFP||Single-mode SFP|
|Optical Fiber Type||62.5/125µm or 50/125µm core MMF.||9/125µm core SMF.|
|Working Wavelength||Mainly in 850 nm and 1300 nm.||Mainly in 1310 nm and 1550 nm|
|Color Coding||Black color coded bale clasp.||Blue color coded bale clasp for 1310nm SFP. Yellow color coded bale clasp for 1550nm SFP.|
|Fiber Cable Jacket Color||Orange jacket for OM1 & OM2.||Yellow jacket for SMF.|
|Transmission Distance||Short distance transmission such as 100 m and 500 m.||Long distance transmission such as 2 km, 10 km, 20 km, 40 km, 80 km, 100 km and 120 km.|
|Price||Cheaper than SMF SFP.||Higher cost than MMF SFP.|
Apart from the above mentioned SFP transceivers that use dual fibers for duplex transmission (one transmit and one receive separately), there are SFP transceivers that use only a single fiber for transmission. The latter are called simplex SFPs, or more commonly known as bidirectional (BiDi) SFPs, which are equipped with WDM couplers/diplexers. The most frequently used wavelength pairs of BiDi SFPs are 1310nm/1550nm, 1310nm/1490nm and 1510nm/1590nm. And the transmission distances vary from 10 km to 160 km when using different wavelengths. It is very easy to distinguish simplex SFP and duplex SFP from the receptacle.
Figure 3: Duplex SFP with dual fiber port and simplex SFP with single fiber port.
All SFP transceivers should be used in pairs. For duplex SFPs at the two sides, we should connect two SFPs of the same wavelengths. For example, two 850nm SFPs or two 1310nm SFPs. However, for simplex/BiDi SFPs, we should use two SFPs that have opposite wavelengths for transmitter and receiver, which has more detailed introduction in the post A Brief Introduction of BiDi SFP Transceiver.
As an advanced technology that allows to transmit multiple signals simultaneously on a single fiber, wavelength-division multiplexing (WDM) is utilized by telecom systems in long distance transmission, either DWDM (dense WDM) or CWDM (coarse WDM). In these systems, the lasers of SFP transceivers are chosen with precise wavelengths closely spaced but not so close they interfere with each other.
Figure 4: 18 wavelengths CWDM SFP with different color coded bade clasps.
CWDM SFPs and DWDM SFPs both connect with LC duplex single-mode fiber cables, but they have more differences than similarities. Generally, when the customer needs a number of channels up to 16, it is more economical to deploy CWDM SFP vs. DWDM SFP. For information about how to choose CWDM SFP+ and DWDM SFP+, you can read the article: Everything You Need to Know Before Buying CWDM and DWDM SFP+ Transceivers.
|Specifications||CWDM SFP||DWDM SFP|
|Wavelength Spacing||Up to 18 wavelengths from 1270 nm to 1610 nm with a 20nm spacing, i.e. 1270 nm, 1290 nm, 1310 nm, 1330 nm...||Up to 45 wavelengths ( Channel 17 to Channel 61 according to ITU) of C Band (1525 nm to 1565 nm) or L Band (1570 nm to 1610 nm) with a 0.8nm spacing.|
|Modulation Laser||Electronic tuning uncooled laser.||Cooling laser which adopts temperature tuning enables DWDM SFP better performance, higher safety and longer life span.|
|Transmission Distance||Up to 100 km, typically 80 km.||Up to 80 km or 200 km.|
|Application||Gigabit Ethernet, Fibre Channel (FC), Metro Access Network, Point-to-Point Network, Synchronous Optical Network (SONET), SDH (Synchronous Digital Hierarchy).||Long distance DWDM SONET/SDH transmission, Gigabit Ethernet, Fibre Channel, Metro Network.|
|Benefits||Passive equipment that uses no electrical power. Much lower cost per channel than DWDM. Scalability to grow the fiber capacity as needed with little or no increased cost. Protocol transparent. Ease of use.||Up to 32 channels can be done passively. Up to 160 channels with an active solution. Active solutions involve optical amplifiers to achieve longer distances.|
|Drawbacks||16 channels may not be enough. Passive equipment that has no management capabilities.||DWDM solutions are quite expensive. Active solutions require a lot of set-up and maintenance expense. Very little scalability for deployments under 32 channels.|
3G-SDI (serial digital interface) video SFP transceivers are designed to meet the high standard video transmission needs in the High Definition (HD) environment. The key difference between video SFPs and normal SFPs is that, the video transmission is uni-directional. Thus, the video SFP can have either two optical transmitters, two optical receivers, a single transmitter, a single receiver, or one optical transmitter and one receiver. Similar to normal SFP transceivers, 3G-SDI video SFPs can be multimode, single-mode, BiDi or CWDM transceivers of different wavelengths, and can have different reaches of distances. More details about video SFP transceivers, please read Understanding Video SFP Transceivers.
Passive Optical Networking is the key technology used in fiber-based (FTTx) access networks. PON SFP transceivers are used in the Optical Line Terminal (OLT) at the Central Office and the Optical Network Terminal/Unit (ONT/ONU) at subscriber’s premises. PON SFP differs from other SFP transceivers in that the OLT SFP and ONT SFP are not used in pairs, instead an OLT SFP should communicate with up to 32 or 64 ONT SFPs. Generally, GPON SFP consists of two types: Class B+ and Class C+. Here are their differences.
|Transceiver Type||Class B+||Class C+|
|Ports||Tx power||Max. Rx sensitivity||Tx power||Max. Rx sensitivity|
|GPON OLT SFP||1.5-5 dBm||-28 dBm||3-7 dBm||-32 dBm|
|OLT SFP Operation Wavelength||1480-1500 nm||1260-1360 nm||1480-1500 nm||1290-1330 nm|
|GPON ONT SFP||0.5-5 dBm||-27 dBm||0.5-5 dBm||-30 dBm|
|ONT SFP Operation Wavelength||1260-1360 nm||1480-1500 nm||1290-1330 nm||1480-1500 nm|
The trend towards higher speed and higher bandwidth is always unstoppable, from Fast Ethernet to Gigabit Ethernet, and then to 10 Gigabit Ethernet and 25 Gigabit Ethernet. At the same time, new devices for transmitting data are published, SFP+ for 10 Gigabit and SFP28 for 25 Gigabit Ethernet. The most obvious difference between them is the data rate, while they all use the same form-factor packaging. Let see what’s the difference SFP vs. SFP+ vs. SFP28.
|Data Rate||1.25G 2.5G/3G/4.25G||6G/8.5G/10G||25G|
|Types||Single-mode/Multimode Simplex/Duplex CWDM/DWDM||Single-mode/Multimode Simplex/Duplex CWDM/DWDM||Single-mode/Multimode (by the time when this post was written)|
|Distance||100 m/300 m/2 km/ 10 km/15 km/ 20 km/40 km/ 60 km/80 km/ 100 km/120 km/ 150 km||220 m/300 m/ 2 km/10 km/ 20 km/40 km/ 60 km/80 km||100 m/10 km (by the time when this post was written)|
|Wavelength||850 nm 1310 nm/1490 nm/1550 nm 1270 nm-1610 nm ITU Channel 17 ~ Channel 61||850 nm 1310 nm/1490 nm/1550 nm 1270 nm-1610 nm ITU Channel 17 ~ Channel 61||850 nm/1310 nm (by the time when this post was written)|
For these transceivers with the same packaging, a lower speed optical transceiver can be plugged into the slot of higher speed and work at the lower data rate, such as an SFP can be used in an SFP+ slot for 1G transmission, but the contrary is not feasible.
Regardless of any specific switches/routers/servers, it will be hard to figure out which SFP transceiver is proper in use when facing so many types of SFP modules. But you could get away with these problems when you choose FS. Not only all the SFP types can be supplied, but also with free technical support for connections between whichever device customers have, whether it is generic- or original-branded. Every SFP module will be compatibility and quality ensured before it is sent to you. Just throw your questions about SFP transceivers to FS and let us help solve them.Related Article: SFP Module: What’s It and How to Choose It?
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