Different types of transceivers

Different types of transceivers

There’s a lot to consider when building a fiber optic network. There are so many different ways to approach optical communication, and every device has its own list of pros and cons. In modern, dense networks, small form factors are a constant necessity. Without such interfaces, you simply can’t pack enough networking components into the limited space that is always constricting the network’s design. That’s why so many form factors have emerged. This simple guide is going to help you map the differences between GBIC, SFP, SFP+, SFP28, QSFP, QSFP+, QSFP28 and CFP. With it, at least some of your networking decisions should come a little more easily.

GBIC (Gigabit Interface Converter)

A gigabit interface converter (GBIC) is a transceiver that converts electric currents (digital highs and lows) to optical signals, and optical signals to digital electric currents. The GBIC is typically employed in fiber optic and Ethernet systems as an interface for high-speed networking. The data transfer rate is one gigabit per second (1 Gbps) or more. This is the first generation of all transceiver modules which was invented in the year 2000.

GBIC modules allow technicians to easily configure and upgrade electro-optical communications networks. The typical GBIC transceiver is a plug-in module that is hot-swappable (it can be removed and replaced without turning off the system). The devices are economical because they eliminate the necessity for replacing entire boards at the system level. Upgrading can be done with any number of units at a time, from an individual module to all the modules in a system.

SFP (Small Form-factor Pluggable)

Usually, SFP is considered an upgraded version of the GBIC module. However, GBIC and SFP are equal in performance. The only major difference between them is their size. SFP module is much smaller than the GBIC module. For this reason, the SFP is also called mini GBIC which was developed in 2001. These years, due to the small size of SFP, GBIC module is being replaced by SFP. Why is this happening? In fact, the most common reason is that the big size of the GBIC module was not feasible to provide a number of interfaces on a line card or a switch since it occupies more space.

In my previous article, you might have seen basics of SFP transceivers available in the market. The evolution of these transceivers didn’t stop here too. Even though SFPs are the most widely used transceivers there is many more SFP varieties are available which is based on the data transfer rate and maximum distance it can cover. Let us have a look at these models also.

SFP+

SFP+ takes the benefits of the SFP design and improves on their data capacity. SFP+ still functions with copper and optical cabling, but it can achieve much higher speeds. SFP+ is made to operate at 10Gb/s. Classified by the host interface, the SFP+ fiber optic transceiver can be divided into linear and limiting transceivers. The linear SFP+ module is most appropriate for 10GBase-LRM; otherwise, a limiting module is preferred with the reason that it contains a signal amplifier to re-shape the degraded (received) signal whereas linear does not.

SFP 28

SFP28 stands for Small Form-Factor Pluggable 28. It is the third generation of the SFP interconnect systems designed for 25G performance per the IEEE 802.3by specification (25GBASE-CR). SFP28 has the same common form factor as the SFP+ but supports 25Gbps electrical interfaces per channel. SFP+ and SFP28 transceiver has the same pinouts and they are mating compatible.

Given the fact that SFP28 is compatible with SFP+ ports, here comes the question: is it possible to connect SFP28 ports with SFP+? The answer is definitely yes: SFP28 adopts the same form factor as SFP+, just running at 25 Gb/s instead of 10Gb/s, which offers better performance and higher speed. So SFP28 will work sufficiently on SFP+ ports, and SFP+ cables can be plugged into SFP28 ports although they are not designed for 25Gb/s data rates. When it comes to copper cable, SFP28 copper cable possesses significantly greater bandwidth and lower loss compared with the SFP+ version.

XFP

XFP has appeared before the SFP+. It is also a standardized form factor for serial 10 Gb/s fiber optic transceivers. Principal applications include 10 Gigabit Ethernet, 10 Gbit/s Fiber Channel, synchronous optical networking (SONET) at OC-192 rates, synchronous optical networking STM-64, 10 Gbit/s Optical Transport Network (OTN) OTU-2, and parallel optics links.. XFP transceivers are used in data communication and telecommunication optical links and offer a smaller footprint and lower power consumption than other 10 Gb/s transponders. The electrical interface to the host board is a standardized serial 10 Gb/s interface called XFI. XFPs are slightly bigger than SFP modules in size.

QSFP(Quad Small Form-factor Pluggable)

Another expansion on the original SFP concept, QSFP uses double fiber pairs. The Q stands for “quad,” and the additional pair allows for substantially more powerful data transmission. QSFP data rates get up to 1 Gbps per channel, allowing for 4X1 G cables and stackable networking designs that achieve better throughput. QSFP connectors are still small(slightly bigger than SFPs) and hot-pluggable, and they still support Ethernet and fiber optics. Added to the supported list is InfiniBand.

QSFP+( Quad Small Form-factor pluggable plus)

QSFP+ is the modern incarnation of QSFP. The difference is only the data transfer rate in QSFP+ is much higher than QSFP. In most data centers, it has completely replaced its predecessor. QSFP+ can reach speeds of 10 Gbps per line. QSFP+ has four-channel SFP+ interfaces that can transfer rates up to 4x10Gbps or 1x40Gbps depending on the transceiver used.

QSFP28(Quad Small Form-factor pluggable 28)

The latest advance on QSFP connections is QSFP28. The 100G QSFP28 transceiver module is a high-density, high-speed product designed for 100Gbps applications. It has the same form factor as the QSFP+ transceivers. QSFP28 100G optics offers four channels of high-speed differential signals with data rates ranging from 25 Gbps up to potentially 40 Gbps, and finally, meet 100 Gbps Ethernet (4×25 Gbps) and 100 Gbps 4X InfiniBand Enhanced Data Rate (EDR) requirements. QSFP28 transceiver recently is typically available in several standards—100GBASE-SR4, 100GBASE-LR4, 100GbASE-PSM4 and 100GBASE-CWDM4. QSFP28-100G-SR4 operates over multimode fiber for a distance of 100 m. While 100GBASE-LR4 QSFP28 supports a much longer distance of 10 km. Compared with CFP form factors, QSFP28 optics are more popular on the 100G optics market.

CFP(C form-factor pluggable)

CFP is a multi-source agreement to produce a common form-factor for the transmission of high-speed digital signals. The c stands for the Latin letter C used to express the number 100 (centum) since the standard was primarily developed for 100 Gigabit Ethernet systems. It can support a wide range of 40Gb/s, 100Gb/s and 400Gb/s applications, including next-generation High-Speed Ethernet (40GE, 100GE and 400GE). Pluggable CFP, CFP2, CFP4 and CFP8 transceivers will support the ultra-high bandwidth requirements of data communication networks that form the backbone of the internet. The most recent CFP8 transceiver form factor provides for a very versatile platform that can support a broad range of PMD’s at 400G and importantly offers a path to products in the future that are capable of supporting 800Gb/s.

Classified by application, which means that all of the above transceivers can be used with multiple fiber optics technologies such as BiDi, CWDM, DWDM the data transfer rate and distance can be maximized. For this purpose, various BiDi modules, CWDM modules, DWDM modules of all of the above transceivers can be purchased.

Knowledge & picture Credits: www.fs.com

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The meaning of SR, LR, LRM, ER, and ZR in Transceiver Modules

When you take transceiver modules, all of this will contain many abbreviations which may be quite confusing for you too. In fact, these abbreviations tell you the characteristics of these modules. Let us have a look into some of this in detail.

SFP-10G-SR vs SFP-10G-LR vs SFP-10G-LRM vs SFP-10G-ER vs SFP-10G- ZR is the most common scene abbreviations in almost all SFPs. What are the similarity and differences? Now let us make a comparison of the similarity and difference, it will help you choose the right 10G SFP+ module depends on your application.

When you are looking at these terms SR, LRM, LR, ER, ZR used in fiber optic communications that stand for the transmission distance of these modules. Here we have considered only 10Gbps SFPs only to learn about its transmission capacity.

Let us see that the case of Multimode Fiber

10GBase-SR

SR stands for Short Range, these transceivers support link length of 300m over multi-mode fiber and use 850nm lasers. 10GBase-SR is the original multimode optics specification and is still by far the most commonly used.  

10GBase-SR it uses a single, low-cost solid-state laser assembly, it is also the least expensive of the optical modules available for a 10GbE platform. However, 10GBase-SR is very sensitive to fiber type. Its Physical Coding Sublayer 64b/66b PCS is defined in IEEE 802.3 Clause 49 and its Physical Medium Dependent PMD in Clause 52. It delivers serialized data at a line rate of 10.3125 Gbit/s.

10GBase-LRM

LRM means Long Reach Multimode, these transceivers support distance up to 220m over multi-mode fiber and use 1310nm lasers. The replacement to 10GBase-LX4, 10GBase-LRM will reach up to 220m over standard multimode fiber, but without the complexity of the 10GBase-LX4 optics.  Instead, a single laser operating at 1310nm is used.  This allows LRM optics to be packaged in XFP and SFP+ form factors.

Let us see that the case of Single-mode Fiber

10GBase-LR

LR means Long Reach, these transceivers support distance up to 10km over single-mode fiber and use 1310nm lasers.  There is no minimum distance for LR, either, so it is suitable for short connections over single-mode fiber as well. 

10GBase-ER

ER means Extended Reach, Basically, these are just extremely long-range fiber variations. 10GBASE-ER has a reach of 40 kilometers over-engineered links and 30 km over standard links. Due to the laser power, attenuation is required for links less than 20km long.

10GBase-ZR

ZR also stands for Extended Reach which can transmit a 10Gbps data rate and 80km distance over single-mode fiber and use 1550nm lasers. Due to the very high transmit power, significant attenuation is needed for shorter links. ZR is actually an unofficial format, which is not technically part of the IEEE 802.3ae standards for networking hardware. Use of ZR optics should be preceded with an optical power test of the fiber span in question to ensure a problem-free deployment.  Several hardware manufacturers -including Cisco- have their own implementations of ZR, but they aren't necessarily cross-compatible. 

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A Study about SFP Modules

A small form-factor pluggable (SFP) transceiver is a compact, hot-swappable, input/output transceiver used in data communication and telecommunications networks. SFP interfaces are generally used in almost all communication devices like switches, routers, and servers. SFP transceivers support communications standards including synchronous optical networking (SONET)(Standardized protocols that transfer multiple digital bit streams synchronously over optical fiber using lasers or highly coherent light from light-emitting diodes (LEDs).), Ethernet and fiber channel. Hence the availability of SFP modules can be either for fiber optic cables or copper cables.

SFP Transceivers have a wide range of detachable interfaces to multimode/single-mode fiber optics, which allows users to select the appropriate transceiver according to the required optical range for the network. SFP transceivers are also available with copper cable interfaces, which allows a host device designed primarily for optical fiber communications to also communicate over unshielded twisted pair networking cables. 

Functionality of SFP Modules

The simplest way to describe the functionality of SFP modules is that these are transceivers(a device that transmits and receives)which can also convert signals from one form to another form. As you know the machines can process the data only in the form of digital signals(1’s & 0’s), In the case of data transmission through fiber optic cables, data has to be converted into light signals. Here SFP modules will convert digital signals to light signals on the sender side and light signals to digital signals on the receiver side. When it comes to copper cable communications, digital signals are converted as electric signals (analog signals). The  SFPs used in this scenario can act as Digital to Analogue Converter (DAC) and Analogue to Digital Converter (ADC).

Modern optical SFP transceivers support digital diagnostics monitoring (DDM) functions, also known as digital optical monitoring (DOM). This feature gives users the ability to monitor the real-time parameters of SFP, such as optical output power, optical input power, temperature, laser-bias current and transceiver supply voltage.

Evolution of SFP Modules

With the increasing demand for higher bandwidth, multiple types of transceiver modules are designed for data transmission, including GBIC, SFP, SFP+, XFP, QSFP, QSFP+ and so on. Well, what do GBIC, SFP, SFP+, and QSFP stand for? Among them, SFP has been used in popularity for over 18 years.

The first generation of a transceiver is GBIC (Gigabit interface converter), which is a hot-swappable transceiver developed in 2000. However, with the demand for higher bandwidth and faster transmission speed, The Small Form Factor Committee, a group consisting of major equipment vendors, created the Mini GBIC(SFP) specification and first published it in 2001. SFP modules built to the initial specifications support data rates of up to 1 Gb. The specification has since been updated to support increased data rates.

The most common name used for Mini GBIC is nothing but the SFP which has replaced GBIC in most applications for the small size. Just as its name, Mini GBIC is similar to the former GBIC in function but with a smaller form factor. It provides flexibility for the transmission in both data and telecommunication applications. Instead of being standardized by official standards, SFP is specified by the multi-source agreement (MSA). MSA is an agreement between many different transceivers manufactures to make standardized products. So the SFP is compatible across a range of telecoms vendors’ hardware. In addition, SFP module can be categorized into various types 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, 1000BASE-ZX, 1000BASE-SR and so on.

SFP Transceivers Over Copper Cabling: 1000BASE-T vs. 1000BASE-TX

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. Below table will give you a better idea of each of these SFPs specifications.

Though 1000BASE-TX needs fewer 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 Over Optical Fiber Cabling

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 ,1000BASE-ZX and 1000BASE-SR. Have a look at the below table which will give you a better idea of each of these SFPs specifications.

SFP modules designed for use with fiber support a variety of wavelengths and maximum distances up to 2 km with multimode and 100 km with a single-mode. 
If you ever wonder why SFP Transceivers over copper cabling is limited than SFP transceiver over fiber cabling, the answer is simple, it’s due to the distance limitation of UTP/STP cables(maximum up to 100m) and its noise disruption characteristics.

Optical SFP Transceivers of Different Fiber Types

We all know that there are two types of fiber optics cables are available. Hence the use of SFP transceivers that work over optical fiber 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.

The primary function to meet the communication using SFP’s are, both the end to end must have similar components. Let’s say for example if you want to interconnect two switches using SFP ports, If this is a single-mode fiber optics cable communication then both the SFP modules used in both the end should be single mode. If this is a multi-mode fiber communication then both the SFP modules which are used in communication should support multimode communication. So let’s say that we can’t make the communication channel by using different mode components. 

Single-mode SFP vs. Multimode 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.

Simplex SFP & Duplex 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. BiDi SFPs support bidirectional communication over a single fiber. While other SFP types require two fibers -- one to send and one to receive -- BiDi SFPs use different wavelengths with one wavelength for sending data and the other for receiving. 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.

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.

Long-Reach WDM SFP Transceivers of Multiple Wavelengths

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.

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

Video SFP Transceivers for High-Quality Video Services

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.

PON SFP Transceivers in FTTx Networks

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 the 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.

Advancing to Higher Speed: From SFP to SFP+ and SFP28

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.

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.

Knowledge & Picture credits: www.fs.com

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