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Fiber Link Power Budget: How to Make It Right?

Fiber Link Power Budget: How to Make It Right?

In optical communication system, fiber patch cables and optical transceivers are necessities to complete the pathway for optical signal, enabling data to transmit between devices. To ensure that the fiber system has sufficient power for correct operation, it is vitally important to calculate the span’s power budget. A solid fiber link performance assures the networks run smoother and faster, with less downtime. This article addresses the essential elements associated with link power budget, and illustrates how to calculate power budget effectively.

Power Budget Definition

Power budget refers to the amount of loss a data link can tolerate while maintaining proper operation. In other words, it defines the amount of optical power available for successful transmitting signal over a distance of optical fiber. Power budget is the difference between the minimum (worst case) transmitter output power and the maximum (worst case) receiver input required. The calculations should always assume the worst-case values, in order to ensure the availability of adequate power for the link, which means the actual value will always be higher than this. Optical power budget is measured by dB, which can be calculated by subtracting the minimum receiver sensitivity from the minimum transmit power:

PB (dB) = PTX (dBm) – PRX (dBm)

fiber link power budget

Why Does Power Budget Matter?

The purpose of power budgeting is to ensure that the optical power from transmission side to receiver is adequate under all circumstances. As data centers migrate to 40G, 100G and possible 400G in the near future, link performance becomes increasingly essential. Link failures would stir up a sequence of problems like system downtime, which equates to accelerated costs, frustrated users, deteriorated performance and increased total cost. While with appropriate power budgeting, a high-performance link can be achieved for better network reliability, more flexible cabling and simplified regular maintenance, which is beneficial in the long run.

Critical Elements Involved In Calculating Power Budget

When performing power budget calculation, there are a long list of elements to account for. The basic items that determine general transmission system performance are listed here.

link power budget vs. distance

Fiber loss: fiber loss impacts greatly on overall system performance, which is expressed by dB per kilometer. The total fiber loss is calculated based on the distance × the loss factor (provided by manufacturer).

Connector loss: the loss of a mated pair of connectors. Multimode connectors will have losses of 0.2-0.5 dB typically. Single-mode connectors, which are factory made and fusion spliced on will have losses of 0.1-0.2 dB. Field terminated single-mode connectors may have losses as high as 0.5-1.0 dB.

Number and type of splices: Mechanical splice loss is generally in a range of 0.7 to 1.5 dB per connector. Fusion splice loss is between 0.1 and 0.5 dB per splice. Because of their limited loss factor, fusion splices are preferred.

Power margin: power budget margin generally includes aging of the fiber, aging of the transmitter and receiver components, additional devices, incidental twisting and bending of the fiber, additional splices, etc. The margin is needed to compensate for link degradation, which is within the range of 3 to 10 dB.

How to Properly Calculate Power Budget?

Here we use the following example to demonstrate how to calculate power budget of an optical link: Example: the system contains the transmitter and receiver, the optical link contains optical amplifier, 4 optical connectors and 5 splices. The following table presents attenuation or gain of each components.

Tx power:   3dBm

Connector loss: 0.15dB

Splice loss: 0.15dB

Amplifier gain: 10dB

Fiber optic loss: 0.2 dB/km

fiber link power budget calculation

The total attenuation of this link PL is the sum of:

Fiber optic loss: (30 km + 50 km) ×0.2dB/km = 16 dB

Attenuation of connectors: 4×0.15 dB = 0.60 dB

Attenuation of splices: 5×0.15 dB = 0.75 dB

So PL = 16 Db + 0.60 Db + 0.75 Db = 17.35 dB

The total gain of the link is generated by optical amplifier, which is 10 dB in this case. So PG = 10 dB

Considering link degradation, power margin should be calculated as well. A good safety margin  PM = 6 dB

To select the receiver’s sensitivity at the end of the optical path, it is sufficient to rearrange and solve the equation. So:

Ptx – Prx < PL – PG + PM

Prx > Ptx – PL + PG – PM

Prx > 3 dBm – 17.35 dB +10 dB – 6 dB

Prx > -10.35 dB

The receiver should provide sensitivity better than -10.35 dBm.

Conclusion

With data centers migrating to 40G, 100G, 200G and even 400G, fiber link performance becomes more important than ever before. Understanding link power budget will help you optimize your fiber link design as well. In addition, high-performance cables, quality transceivers and high-performance installation practices also assist to ensure better link performance.

Cleaning Recommendation for Optical Transceiver

Cleaning Recommendation for Optical Transceiver

We have always emphasized that proper fiber cleaning of connector end-face is very important to ensure the performance of the whole fiber systems. In fact, optical transceiver module is no exception as the contamination of the optical port of a transceiver will also lead to network failure. However, many people overlook the importance of optical transceiver cleaning or do not clean it in a proper way. This is why I want to talk this topic today.

When to Clean?

As we know, the connector end-face of fiber jumper is always recommended to clean before connection. But the optical port of the optical transceiver should not need frequent cleaning unless there is a problem because they have less risk of being contaminated compared to jumper. In general, if you have cleaned your connectors, but still experience low-power output from an optical transceiver or a fault signal from your equipment, you should clean the optical port of the transceiver.

interface

How to Clean

The best way to clean the optical port of a transceiver is to use the air duster (also called clean dry air) to blow away small dust particles. In addition, lint-free stick/swab is also required for dry cleaning. The detailed cleaning procedure is shown as below:

  • Remove the dust cap from the optical transceiver.
  • Use an air duster to remove any dirt or particles.
  • Insert a lint-free stick of the appropriate size (2.5 mm or 1.25 mm) and turn clockwise. Dry cleaning is recommended here. Thus, Don’t use alcohol-based cleaning sticks.
  • Repeat steps 2 and 3 if necessary.
  • Remove the lint-free stick and reinsert the dust cap to the transceiver. Always keep the dust cap inserted in the transceiver when not in use.
  • Place the transceiver on a clean and static-free area, such as an antistatic mat.

cleaning tool

Tips: To prevent cross contamination, always make sure that the connector of jumper that will be plugged into the transceiver is cleaned before connection.

Summary

Optical ports of transceivers also require proper cleaning to ensure the fiber transmission performance. It is recommended to clean the transceiver port when there is an error on port. Dry cleaning is recommended to use with air duster and lint-free. Moreover, cross contamination should be avoided by always using cleaned jumper. For more information about fiber optic cleaning, please visit here.

3rd-Party Optical Transceivers Testing & Verification

3rd-Party Optical Transceivers Testing & Verification

fiber optic transceiverOverview

As the technology and market of fiber optic transceivers continue to mature, 3rd-party optical transceivers are now widely used in optical transmission solutions. In order to ensure compliance, 3rd-party optical transceivers need to be tested and verified before inserting to the device. This paper will talk something about the testing and verification methods of 3rd-party optical transceivers.

Why Are 3rd-Party Optical Transceivers So Popular?

Nowadays, people prefer to use 3rd-party optical transceivers rather than officially-branded’s. The increasing market demands of 3rd-party transceivers illustrate the point. There is absolutely no difference between an officially-branded transceiver and a 3rd-party plug. As long as transceivers meet the international standards, there is no question of compatibility between fiber optic transceiver modules. Actually, most “third party” transceivers are made and assembled in exactly the same plants assembling officially-branded transceivers. In addition, it is very, very unlikely that a transceiver module will damage a switch. The primary benefit is the cost savings. The difference in price often exceeds 80 percent or more. Because transceiver costs are a significant part of the total system cost, it is important for designers to minimize these costs. With the significant savings, designers can re-invest and make their designs better. This is why 3rd-party transceivers are more and more popular with users.

Testing & Verification Are Necessary

There are methods to test and verify the 3rd-party transceiver modules, but it’s not always as easy as it seems. It was easier when the entire network was owned by a single company. As long as the system worked, there was no need to test all the subcomponents extensively. Now, you have so many components from so many different suppliers that you’ll need a test strategy to ensure that all components will meet the system level requirements. Here’s what you need to know if you’re considering testing and verifying in today’s world.

Test for an Acceptable Bit-Error Ratio

In a digital communications system, you must always operate within an acceptable bit-error ratio (BER). This is true whether you are testing an interface bus in a laptop computer or a telecommunications link. In general, when you’re testing in a digital communications system, it should be no more than one error in 1012 bits. If the desired BER is not reached, it must be determined if the problem is in the transmitter, receiver, or both.

Test to Determine Interoperability With a Worst-Case Transmitter

Network specifications should determine if the worst-case transmitter will interoperate with a receiver. Transmitters should also have a signal sufficient enough to support the worst-case transceiver.

Determine the Minimal Power Level & Jitter Level

A receiver will need to achieve a minimum power level to achieve the BER target. The level achieved will dictate the minimum allowed output power. Likewise, if the receiver can only achieve a certain level of jitter, this will be used to define the maximum amount of jitter that can be received from the transmitter without malfunctioning. Transmitter parameters may specify the wavelength and the output waveform shape.

Try Performing the Optical Eye-Mask Tests

You can perform optical eye-mask tests with oscilloscope, e.g. digital communications analyzers. Laser manufacturers will need their lasers to pass the tests without violations. Measurements will also need to be made within a significant margin.

Verify Compliance With Multiple Samples

Several waveform samples are required to remain compliant. Sometimes, a larger population of waveform samples will provide an accurate assessment of transmitter performance. The oscilloscope will collect more data, but as more samples are increased the likelihood of mask violations increase. Since the results are either pass or fail, it is important to acquire as many samples as possible to get an accurate assessment, which requires aligning the mask to the waveform.

Consider Expanding Your Eye Mask

When you expand the eye mask, you can verify a compliant hit ratio. Only a small number of samples are capable of intersecting a mask. Most oscilloscopes will include a modified version of the classic eye-mask test. Once you have the desired number of samples, you can determine how far you can expand the mask. Each test will determine how far you can expand the mask before the mask hits to the total waveform exceeds the ratio.

Know About Instrumentation Effects

Keep in mind that any transceiver test can be skewed based on the oscilloscope’s frequency response. You can achieve consistent results with a reference receiver. Most tests will use a fourth-order Bessel filter response, and the 3-dB bandwidth is at 75 percent of the data rate.

These are just a few ways to test and verify third-party optical transceivers. If you follow these tests and avoid the pitfalls, you’ll be able to test and verify your 3rd-party optical transceivers with ease.

How to Use DOM for All Transceivers Type in The Cisco System

How to Use DOM for All Transceivers Type in The Cisco System

hot-swappable-transceiverDo you know that there is a fiber tester inside your optical transceiver? This “fiber tester” we call it DOM, which is short for Digital Optical Monitoring. DOM is a feature which enables the monitoring of some interesting status values on the interface with the most useful values being the optical receive and transmit powers. You can configure your Cisco (or other brand) device to monitor optical transceivers in the system, either globally or by specified port(s). When this feature is enabled, the system will monitor the temperature and signal power levels for the optical transceivers in the specified port(s). CONSOLE messages and SYSLOG messages are sent when optical operating conditions fall below or rise above the optical transceiver manufacturer’s recommended thresholds. By being able to monitor transmit and receive power levels of optical interfaces you are able to characterize the fiber loss and isolate any unidirectional connectivity issues. So, how to use DOM for your optical transceiver in Cisco system is our main topic today.

What Parameters are Monitored by DOM?

DOM allows to monitor some parameters so that network administrators can then check and ensure that the module is functioning correctly. These real-time operating parameters include:

  • Optical Tx power
  • Optcal Rx power
  • Laser bias current
  • Temparature
  • Transceiver supply voltage
How to Use DOM
Restrictions

There are some restrictions of using DOM in Cisco system including:

  • Ensure that your optical transceiver supports DOM. For Cisco original optical transceivers, you need the transceiver module compatibility information for configuring transceiver monitoring. (See Compatibility Matrix)
  • In case of combo ports with SFP and RJ45 provision, when SFP is inserted in slot or port and media type is not configured to SFP, DOM is functional only if global transceiver monitoring is enabled.
  • CISCO-ENTITY-SENSOR-MIB traps are sent only once after the threshold violation. However, SYSLOG traps are sent according to the monitoring interval.

 

Procedure
Command or Action Purpose
Step 1 enableExample: Router> enable Enables the privileged EXEC mode.• Enter your password if prompted.
Step 2 configure terminalExample: Router# configure terminal Enters the global configuration mode.
Step 3 transceiver type allExample: Router(config)# transceiver type all Enters the transceiver type configuration mode.
Step 4 monitoringExample: Router(config-xcvr-type)# monitoring Enables monitoring of all optical transceivers.
Step 5 monitoring intervalExample: Router(config-xcvr-type)# monitoring interval 500 (Optional) Specifies the time interval for monitoring optical transceivers. Valid range is 300 to 3600 seconds, and the default value is 600 seconds.

In conclusion, there are three main command that can be used to turn on/off DOM for all transceivers type in the system:

  • Router(config)#transceiver type all
  • Router(config-xcvr-type)#monitoring
  • Router(config-xcvr-type)#end

Once enabled, DOM can be accessed via CLI using “show interface transceiver command“, shown as the following picture:

show_interfaces_transceiver

DOM is incredibly handy when troubleshooting fiber issues. A low value in the Rx Power column indicates that you have a bad fiber, or more commonly, a dirty fiber optic patch cable somewhere.

Of all the five values, two mostly used and relevant values are TX and RX power, and temperature is also used sometimes. The operating range of these three values is unique across all modules and is available in the data sheet. Additionally, there is an extension available for this command, which is also very helpful and is used to check threshold values of the above parameters like temperature, Tx and Rx. The command is “show interface gig x/y transceiver detail“.

How about Non-Cisco Transceiver with DOM

Though DOM is a very helpful functionality of optical transceiver, not all transceivers support DOM in Cisco’s optical transceiver products family. For example, the common SFPs, such as the GLC-LX or GLC-SX units that are used by most network engineers on a day to day basis are not with DOM feature. Why not add this helpful and convenient feature to all transceivers? Actually, Cisco have their own attitude. They think that DOM functionality is worth an extra $300 a pop, putting the cost of a DOM-enabled single mode SFP close to $800. However, DOM functionality is not a novel thing now. Surprisingly, there are some third-party optical transceiver include the DOM functionality but with a low cost. Fiberstore, for instance, as the professional optical transceiver manufacturer and supplier, they can offer Cisco compatible GLC-LX-SM-RGD with DDM or DOM functionality just at $18.00. But if we want to use non-Cisco transceivers, we need a little different approach to get started with DOM of non-Cisco transceivers. To enable support for non-Cisco SFPs, command “Router(config)#service unsupported-transceiver” is necessary.

For more information about optical transceiver with DOM, please visit Fiberstore.com.

Optical Transceiver Module Tutorial From Fiberstore

Optical Transceiver Module Tutorial From Fiberstore

What is an Optical Transceiver module?

Optical Transceiver is a computer chip that uses fiber optic technology to communicate between other devices. This is opposed to a chip that transfers information electrically through metal wires and circuits or by the process of using various wave forms to communicate data. An optical transceiver chip is an integrated circuit (IC) that transmits and receives data using optical fiber rather than electrical wire.

Optical transceivers are typically used to create high bandwidth links between network switches. With the optical transceiver you can also create data transmission links capable of long range transmission.

Tips: Click here to know about the jargons related to fiber optic transceivers.

Development of Optical Transceiver Modules

Optical transceivers play an important role in conveying information across communication channels for Ethernet systems. They act as the all-in-one objects that receive and convey inforamtion, similar to those found in radios and telephone systems. With an optical transceiver, networks save much more space and avoid the need of having a transmitter and receiver apart inside a network. Capable of transmitting information further and faster than older models, the newer transceivers continue to change the way transceivers are used and appear, making for smaller, more compact modules than before. Here is a simple development of the transceivers.

Earliest Modules
SFP Module is one of the earliest transceiver devices which were created for Gigabit Ethernet networks and were preferred for their hot-swappable abilities. GBIC, or Gigabit interface Converters, allowed networks the ability to transmit data across copper or fiber-optic channels, creating a more versatile device than transmitters and receivers. Of course, GBIC modules were also have defect, and many had size and compatibility issues that limited their ability to transmit data across particular distances and at certain wavelengths.

XENPAK Modules
XENPAK became the new standard transceiver with increased support across longer distances and for multiple wavelengths. Unlike GBIC transceivers that sent information across either copper or fiber optic channels, XENPAKs included support for both networks, creating a better, more flexible module. And unlike the bigger GBIC transceivers, XENPAKs were capable of conveying data across short and long distances due to their configuration settings located inside the devices. When utilizing a single-mode configuration, networks create a single ray of light to send data across a long distance, while they use a multimode setup to transmit information across short distances. Both single and multimode fiber optics were utilized by networks, creating the XENPAK device ideal.

10 Gigabit Ethernet
X2 Transceiver and XPAK that the older XENPAK modules could no longer keep up with, were made when the 10 Gigabit Ethernet standard took hold. The smaller, more flexible X2 and XPAK standards allowed for even more support for the different Ethernet standards and were capable of transmitting data across longer distances.

And when the 10G SFP (SFP Plus or SFP+) came into existence, the competing standards of X2 and XPAK couldn’t continue to control the market as they once had any more. SFP+ modules allowed for more configuration standards for networks, providing various wavelength and distance configurations for Ethernet.

 

Principle of Optical Transceiver Modules

Optical transceiver generally includes both a transmitter and a receiver in a single module. The transmitter and receiver are arranged in parallel so that they can operate independently of each other. Both the receiver and the transmitter have their own circuitry so that they can handle transmissions in both directions. The transmitter takes an electrical input and converts it to an optical output from a laser diode or LED. The light from the transmitter is coupled into the fiber with a connector and is transmitted through the fiber optic cable plant. The light from the end of the fiber is coupled to a receiver where a detector converts the light into an electrical signal which is then conditioned properly for use by the receiving equipment.

In a word, the optical transceiver module is the role of the photoelectric conversion. The transmitter converts electrical signals into light signals, and through the fiber optic transmission, the receiving end of the optical signals are converted into electric signals.

How Optical Transceivers Work In Personal Computers

When there is an issue, the pieces that make up the personal computers could be a mystery for many people. Without having an established understanding, we can feel helpless and incapable of fixing even the most basic of problems on ourself. So, it’s necessary to make clear that how the transceivers work in the computers.

Considering that many of us are constantly on the internet, it may be easy to get an understanding of the most basic optical transceivers and how they make it so you can connect an search the internet with ease. To provide you with a straight connection to the web, you are either connected through a wireless network, or to an Ethernet cable which is connected to your modem or router when you are online. The Cat5 cable as it is also known, plugs into the computer by using the optical transceiver, which is often not housed on the side of your laptop, or the reverse end of the CPU.

There are many various modules that can be utilized as your optical transceiver. Unlike XFP modules, Cisco SFP modules, GigaBit interface converters, or GBIC modules, are some of your more average transceivers, and are input/output modules with one end that plugs into a gigabit ethernet port, while the opposing side is plugged into the fiber patch cables and links the fiber optic networks. Allowing the devices to process the data accordingly, the base function of the GBIC module is to communicate the signals between the Ethernet network and fiber optic network. One terrific aspect of the GBIC module is that it’s a hot pluggable, allotting for a port to be changed from one kind of external interface to another by simply plugging the module in to an alternate external interface without having to power down the host switch or router in the process.

Application of Optical Transceiver Modules

Optical transceiver, essentially just completed the converted of data between different media, can realize the connection between two switches or computers in the 0-120km distance. Its main function is to achieve the conversion between optical-electrical and electrical-optical, including optical power control, modulation transmission, signal detection, IV conversion and limiting amplifier decision regeneration. In addition, there are security information query, TX-disable and other functions. Here is a summary in the practical application.

1. Optical transceivers can realize the interconnection between switches.

2. Optical transceivers can realize the interconnection between the switch and the computer.

3. Optical transceivers can realize the interconnection between computers.

4. Optical transceivers can act as the transmission repeater.
When the actual transfer distance exceeds the nominal transmission distance of the transceiver, in particular, the actual transfer distance exceeds 120km alerts, with 2 sets transceiver back to back in the case of on-site conditions allow, repeaters or the use of “optical-optical” conversiona relay, is a very cost-effective solution.

5. Optical transceivers can offer conversion between single-mode and multimode fiber connection.
When the networks appear to need a single multimode fiber connection, you can use a multimode transceiver and a single-mode transceiver back-to-back connections, which can solve the problem of single multimode fiber converted.

6. Optical transceivers can offer WDM transmission.
The lack of resources of long-distance fiber optic cable, in order to improve the utilization rate of the fiber optic cable, and reduce the cost, transceiver and wavelength division multiplexer (WDM multiplexer) with the use of two-way information on the same fiber transmission.

Classification of Optical Transceiver Modules

Optical Transceiver modules can be classified according to the following aspects.

1. Optical Fiber Type
Single-mode fiber transceiver and Multimode fiber transceiver. The single-mode version has a transmission distance of 20 to 120 km, while the multimode one’s is 2 to 5 km. Due to the different transmission distance, the transceivers’ transmit power, receiver sensitivity and the use of wavelength will be different.

2. Optical Fiber Count
Simplex fiber transceiver and Duplex fiber transceiver. The simplex version receives the data sent in a single fiber transmission, While the duplex one receives data transmitted on a dual fiber transmission. By definition, single fiber devices can save half of the fiber, a fiber that is in the receive and transmit data, where the fiber is very applicable to resource constraints. These products use the wavelength division multiplexing techniques, mostly using the wavelength 1310nm and 1550nm.

3. Transmission Rate
Transmission rate refers to the number of gigabits transmitted per second, per unit of Mbps or Gbps. Optical modules cover the following main rate: low rates, Fast, Gigabit, 1.25G, 2.5G, 4.25G, 4.9G, 6G, 8G, 10G and 40G.

4. Package
SFP, SFP+, GBIC, XFP, XENPAK, X2, 1X9, SFF, 200/3000pin, XPAK
, etc. Click for Details About Related Packages.

 

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