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About DDM, DOM and RGD in SFP Transceiver Module

About DDM, DOM and RGD in SFP Transceiver Module

SFP transceiverIf it is your first purchase of SFP transceivers, you may be very confused with the fuction options “DDM”, “DOM” or “RGD”. So, what functons do they represent? And do you need these functions? Today, we will have a detailed explanation of them.

What’s DDM?
DDM, namely Digital Diagnostics Monitoring, is a technology used in SFP transceivers in order to give the end user the ability to monitor real-time parameters of the SFPs. Such parameters include optical output power, optical input power, temperature, laser bias current, and transceiver supply voltage etc.

What’s DOM?
DOM, short for Digital optical monitoring, is familiar with the DDM function. It is also a feature which allows you to monitor many parameters of the transceiver module in real-time. DOM allows you to monitor the TX (transmit) and RX (receive) of the module, as well as input/output power, temperature, and voltage. Network administrators can then check and ensure that the module is functioning correctly. (Related reading: How to Use DOM for All Transceivers Type in The Cisco System)

Author Note: Obviously a SFP with DDM/DOM funstion is high-ender than one which without it. This is why most of modern optical SFP transceivers support DDM/DOM functions according to the industry-standard SFF-8472.

What’s RGD?
You may be confused with the difference with the SFPs with “RGD” and the one without it, or you may be interested in the “-RGD” in the product number of some SFP transceiver modules, like cisco GLC-SX-MMD-RGD. So, what does RGD stand for? RGD means rugged transceivers. In fact, these are enhanced transceiver modules which have been designed for greater durability, and can operate under more extreme conditions. Rugged transceivers may feature enhanced ESD protection, and extended operating temperature range so that it can help eliminate field failures without the need of costly external protection devices.

Author Note: In general, a rugged SFP can be identified by its product model, ie. -RGD. Specific situations depend on the specific vendors.

Other Functions in SFP transceivers
If you have an experience of buying Cisco SFPs, you may be confused with the part number with “=”, like GLC-SX-MMD vs GLX-SX-MMD=, because you can not find out the difference with the one without “=” according to the specification. In fact, “=” is also called a “FRU” part where FRU stands for “Field Replaceable Units”. Those are the parts that can be used as “spare” or be shipped individually to replace damaged units. But the new parts that are ordered directly from a reseller or from Cisco usually don’t come with the = sign. Thus, if you want to buy an SFP transceiver with the “FRU” part, you should ask your vendor to ensure this function.

Recommended Products With These Functions

When it’s best to use GBIC and When to use SFP?

When it’s best to use GBIC and When to use SFP?

There are many kinds of fiber optic transceiver modules in the market, such as GBIC, SFP, SFP+ and so on. In addition, these 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). In addition, there are a variety of interface types of GBICs and SFPs, like 1000Base-SX, 1000Base-LX/LH, 1000Base-EX or 1000Base-T etc. Faced with too much choice, users are often confused when they need to buy the related products.

Recently many users ask when they choosing a card for their switch/router, they should choose either cards that take SFP or cards that take GBIC. It seems to be a headache for them because they are not clearly know the differences of them. Thus, today, we are mainly going to discuss that when it’s best to use GBIC and when to use SFP.

What Is GBIC (gigabit interface converter)
GBIC is a hot-swappable input/output device that plugs into a Gigabit Ethernet port or slot, linking the port with the network. GBIC is a standard for transceivers, commonly used with Gigabit Ethernet and fiber channel. GBIC module is hot pluggable, this feature allows a suitably designed enclosure to be changed from one type of external interface to another simply by plugging in a GBIC having the alternative external interface. Generally, GBIC is with the SC connector. The GBIC standard is non-proprietary and is defined by the Small Form Factor committee in document number 8053i. The first publication of the proposal was in November 1995. A few corrections and additions were made through September 2000.


What Is SFP (small form-factor pluggable)
SFP is a specification for a new generation of optical modular transceivers. The form factor and electrical interface are specified by a multi-source agreement (MSA). SFP is also known as a Mini GBIC as its function is somewhat similar to the GBIC transceiver while SFP is smaller than it. SFP transceivers are designed to support SONET, gigabit Ethernet, Fibre Channel, and other communications standards. Due to its smaller size, SFP is now more and more widely used for both telecommunication and data communications applications.


GBIC & SFP Interface Types
For every type of GBICs and SFP transceivers, it works with different wavelengths at a designated location or distance. For examples, SX SFP uses 850nm for a maximum of 550 meters, LX SFP uses 1310nm for a maximum 10km, ZX SFP could reach 80km or copper SFP uses a RJ45 interface. We can easily distinguish via the information in their names or models, ie. 1000BASE-T, 1000BASE-SX, 1000BASE-LX/LH, 1000BASE-ZX, 1000BASE-CWDM, or 1000BASE-DWDM. In addition, the DOM function for an SFP is discretionary. It supports the users to locate the real-time working status of SFP. The famous brand of GBICs or SFPs are Cisco, HP, Juniper, Extreme Network and so on. There is a little difference in the features of each brand’s GBICs and SFPs and they support their corresponding brand’s switches/routers.

According to the above definitions of GBIC and SFP, you may have a further understanding on both of them. There is only one difference between GBICs and SFPs. SFP is smaller than GBIC. Because the smaller size of SFP (almost half the volume of GBIC), we can configure double number of ports on the same panel which increases the utilization rates of switches/routers. Other basic functions of SFP is almost the same with the GBIC and they are equal in performance. Though there are some users still using the GBIC as their old divice which can not be updated to support SFP, GBIC will gradually be obsoleted and replaced by SFP. So the answer to the question “When it’s best to use GBIC and When to use SFP?” is obvious. SFP is your choice. Of course, except GBIC and SFP, there are SFP+, XFP, QSFP/QSFP+ etc. new generation of transceivers which can meet all kinds of your requirements. These new types of transceivers will be discussed in other aticle and not state here one by one. If you are interested in them, please focus continuously on my blog. Or if you need these products, Fiberstore will be a good place for you.

Design principles and implementation of multi-function monitoring platform SFP optical module

Design principles and implementation of multi-function monitoring platform SFP optical module

Read by the microcontroller optical modules and CDR-related memory, and in accordance with the parameters that need to be read LCD display real-time, so that the results intuitive and easy to understand. While connected via serial port and external facilitate debugging. In this system, SFP module implemented by CDR I2c bus communication with the microcontroller. fiber optic transceiver module via an external device access signal, the photovoltaic modules into an electrical signal, and then after the clock data recovery CDR, bit error rate, measuring extinction ratio, sensitivity and other parameters with normal test results to see whether the correct comparison. While the optical module is connected via the optical interface with external microcontroller to communicate with the outside world through the serial port for data exchange, each signal via SMA connector leads, as required by coaxial cable to connect the debugger, it is easy to debug.

Optical Module Monitoring Platform Software Design

Software system design structure with a brief description of the microcontroller Atmega128L LCD (Model LM16032) using parallel data transfer, three control bit MCU PA5 ~ 7 and LCD (RS, RW, E) is connected, plus two control LCD display on the Up-key and turn the key down key DownKey and SCM PE5 and PE6 connected to the microcontroller interrupt the way to achieve the appropriate control. SFP microcontroller reads the data from the relevant parameters I2c bus after transmission through parallel to the LCD display. Using the timer mode, so With a frequency greater than 24MHz refresh LCD display.








Main Parameters Read

Temperature parameters read

Because of the module can be used in a high rate of system and has the appearance of small, the layout of the they are usually very compact.In these applications sfp transceiver of rectangular box shape affect the cooling air flow, thus partially weaken the advantages of easy to use, so the temperature inside the module as a useful parameter to measure the long-term stability of the device and device of electro-optic specifications conform to the degree of life.3.2 read voltage parameterIn the SFP working voltage can through sensor installed on the internal PCB circuit for measuring.These measurements can also be used to observe the working voltage drift.And according to the experience can be linked with a given SFP pin or monitoring failure due to the system power supply environment caused by the large voltage fluctuation.

Read bias current

When reliability prediction has been the most effective transceiver module parameter is the laser bias current, typically used in integrated optical transceiver modules are in constant optical output power mode. Through a closed loop feedback circuit to change the laser bias current so as to stabilize the laser output power. Since the laser efficiency and the threshold values ​​are changed with temperature, and many modules are required to change the laser bias current so as to stabilize the optical output power of the laser, the laser bias current if the variation is not as temperature or voltage changes caused, it shows that the laser potential stability problems.

Based on the Test Platform Module Parameters

Bit Error Rate Test

For error test mainly through error instrument, optical module, and the CDR from ring, through error instrument observation error rate is less than 1 hour 10-12.Test procedures and results:

(1) good connection test equipment.

(2) the work continuously for an hour, once every five minutes record error rate.

(3) the bit error rate has been less than 10-12.

How Much Do You Know About SFP Transceivers?

How Much Do You Know About SFP Transceivers?

What is really a SFP transceiver?
SFP transceiver is a hot-pluggable fiber transceiver, of which the SFP stands for Small Form-factor Pluggable. The mechanical, electronic, and optical design and gratifaction derive from a Multi-source Agreement (MSA) within the fiber telecom industry. It is a pluggable form of SFF. SFP may be the interface between a network device mother board and a fiber optic or copper network cable.


Where is a SFP transceiver used?
SFP transceiver is able to support most of the fiber networking standards for example Gigabit Ethernet, Fiber Channel, SONET, along with a quantity of other communications standards. As a compact and hot-pluggable optical transceiver, it is utilized in optical communications for telecommunication and data communication applications. It connects a switch, router, or any other network devices to a fiber cabling plant. SFP transceivers can be found in Metro Access Network, Metro Core Network, Wide Area Networks (WANs), etc.

What types will the SFP transceiver have?
SFP transceiver has an immense variation available, each with different transmitters or receivers. This enables the user to configure and customize the transceiver to get the proper optical reach with either a multimode fiber (multi mode SFP) or single-mode fiber type.

The SFP module commonly is available in four categories which are SX (850nm), LX (1310nm), ZX (1550nm) and DWDM (DWDM wavelengths). All of them have an interface of a copper cable which permits a mother board to speak via UTP (unshielded twisted-pair) network cable. Click here for a good example of 1550 SFP 80km. There also exist a CWDM and single-mode bi-directional fiber optic cables which are 1310/1490nm upstream and downstream.

Tips: FYI, the industry has developed enhancements to the SFP MSA, known as SFP Plus (SFP+), that is designed for higher data rates, lower cost and better thermal performance. By using SFP+ transceivers, data rate at 10 Gbps could be achievable, including the 8 Gigabit Fiber Channel. When compared with XENPAK or XFP type of modules that have all of their circuitry inside, an SFP+ module leaves some of its circuitry to be implemented on the host board.

What benefits will the SFP transceiver have?
Firstly, SFP transceiver is pluggable that makes it easy to alter the optical interface in the last step of card manufacturing. It’s also easy to accommodate different connector interfaces or a mix of SX and LX SFP.

Practically available, the SFP transceiver has the capability transfer rates as high as 4.25 Gbps. XFP, a form factor that is virtually identical to the SFP type, increases this amount by nearly three times, at 10 Gbps. The SFP transceiver is specified making compatible through the MSA between manufacturers, to ensure that different users who may use equipment from various manufacturers and providers can function effectively and smoothly without having to worry about errors and inconveniences.

Digital optical monitoring (DOM) or digital diagnostics monitoring (DDM) functions are based on the modern optical SFP transceiver according to the industry specifications of the SFF-8472 MSA. The consumer has the ability to constantly monitor real-time parameters of the SFP, for example optical input/outp power, supply voltage and laser bias current due to this feature.

A SFP cage is surface mounted to the PCB board to simply accept the transceiver. This not just provides easy replacement and reconfiguration, but additionally eliminates extra manufacturing steps and reduces cost. Because the optical component is taken away from soldering process, SFP transceivers have high optical reliability and permits the use of higher soldering temperatures.

SFP transceiver is a very popular format that’s recommended by a large number of fiber optic component providers. These businesses carry SFP transceivers for those Cisco devices along with transceiver modules for many other manufacturers. So, if you want technology solutions for the networking applications, at this point you know what to consider. Here is a nice web store you can purchase Cisco SFP modules.

SFPs Find The Position In Commercial Market

SFPs Find The Position In Commercial Market

Small Form factor Plug (SFP) is a compact transceiver that is popular in telecommunication and for data communication. It uses a device which contains a parent board and interfaces it to a fiber optic networking cable. SFP is mainly made to hold Gigabit Ethernet and various other standard communications in it.

Wide types of SFPs can be found, providing the customer by having an option to choose among various unique models, which suits the apt needs. They will use different set of transmitter types on it facilitating you to find the desired transceiver. The SFP transceiver gives link for getting the necessary optical reach through the existing optical fiber. For instance you will find optical fibers like single mode fiber and multimode fiber separately for appropriate usage. In every mode there are different group of fibers flexible for the users’ choice.

In general the rate of signal transmission of SFP module ranges from 100Mbps to 4Gbps. The transceivers work on a distance range varying from 500 meters to 100 kilo meters and also the working wavelength for a number of modules are generally 850nm, 1310nm or sometimes 1550nm. This excellent type of transceiver allows an ease to alter and keep in comparison with other traditional modules. The users can certainly and genuinely replace single module of SFP while the process is running rather than replacing the whole board containing large number of modules in it.


SFP transceivers find the position in commercial market having a capacity to vary data rates as much as 4.25 Gigabits in a single second. The upgraded version namely SFP plus or SFP+ supports data rate as high as 10 Gigabits per second. This rate of transfer is Ten times faster than usual Gigabit Ethernet device. The characteristics of 10G SFP are multifold as following:

  • It can be used instantly connecting to internet.
  • It can be hotly plugged and employed for transferring data.
  • It may withstand temperature up to 70 degree Celsius and may even function at zero degrees Celsius.

Some people might think that SFP would consume more current. Actually, it’s not true. SFP consumes less power but is highly efficient in transferring data. In recent times, SFP transceiver can be used for supporting digital diagnostics monitoring (DDM) activities as reported by the standard matching to it. Hence it is employed for digital optical monitoring services. By making use of this element, the user will keep track of the real time limiting factor of the SFP and monitor the optical input power and output power along with temperature and also the voltage way to obtain the transceiver.

There are lots of benefits of using SFP. You could have multiple choices for internet connectivity using this swappable input/output appliance. The device of SFP comes with copper wire interface by which the user can conveniently hold optical fiber communications. It’s now possible to transfer SDI video outputs over the coaxial cable through the 10G SFP copper. There is also CWDM/DWDM support in some single mode fiber transceivers.

Nowadays SFP has numerous commercial applications in SONET network, point to point mode of networking, Gigabit Ethernet, metro access networks, FTTD, routers, switches, bridges, servers, etc. It also finds a lot of demand kept in storage area network, local area network, high-speed computer links and switching system. SFP offers large range of detachable interfaces to UTP or coaxial cables and multimode or single-mode fibers.

About the author:
FIBERSTORE is a famous optical communication supplier, who can offer both SFP and SFP+ transceivers with all of varieties, along with other modules for example GBIC, XFP, XENPAK, X2, etc.