Wavelength Division Multiplexing (WDM) Increases Network Capacity

WDM is a method of separating or combining multiple wavelengths out of or into a single fiber strand with each wavelength carrying a different signal. Using optical filters lets a certain range of wavelengths pass through, while another range is allowed. Thin-film filter technology (TFF) is often used to achieve this effect. Multiple thin layers are stacked and interference effects are created by sequential reflections on the interface between the layers. This lets light reflect for certain wavelengths and pass through for others.
The capacity of a network can be increased cost effectively by using WDM. Two types of WDM are commonly used:
Dense Wave Division Multiplexing (DWDM) devices are mainly used when more wavelengths are required between sites and when the network extends over a very long distance. Forty wavelength channels from 1530 nm to 1570 nm are distributed in the C-band. To increase capacity, DWDM can be overlaid on a CWDM infrastructure.
Coarse Wave Division Multiplexing (CWDM) has 18 different wavelength channels standard, spaced 20 nanometers (nm) apart between 1270 nm and 1610 nm. Most systems only use the top eight channels between from 1470 nm and 1610 nm. CWDM systems have the advantage that they can always be upgraded at a later stage. This limits the initial installation costs. The requirements on the lasers is not severe due to the wide channel spacing, allowing less expensive lasers without any temperature control to be used.
The insertion loss of DWDM and CWDM is typically lower than that of optical splitters. This increases the reach of a network from a centralized office substantially. As every customer has wavelength(s) assigned to them, this provides better security and makes eavesdropping virtually impossible.
WDMs Can Be Utilized In Different Ways:
Add/Drop Vs Mux/Demux.
A multiplexer, also known as a mux, combines several wavelength channels on one fiber, while a de-multiplexer (demux) separates them at the other side. A mux/demux configuration is very useful to increase a fiber’s end-to-end capacity. A mux is normally located at a central office, while demuxes are placed in either a splice closure or cabinet. From there the fibers are routed in a star-shaped topology to their ultimate destination.
An alternative to separating the wavelengths at one side, individual wavelengths can be added or dropped at various points across the line. This process does not affect other wavelengths. This is often preferable when the distance between sites is long or they are grouped in a circular structure.
One Or Two Fibers?
An alternative to sending signals at different wavelengths through the same fiber is to use two different fibers. Many CWDM systems use two fibers where one is used for upstream signals and the other for downstream. In this configuration, each customer uses two fibers and one wavelength. Each customer will have two wavelengths if they use a single fiber.

Utilizing the WDM – Increase Fiber Capacity Without Construction

Imagine turning a dirt road into a multilane highway without having to perform any new construction. That is what Wave Division Multiplexing (WDM) allows with an existing fiber network. This technology can greatly reduce the cost of increasing network capacity without having to move a single shovelful of dirt or hang a single new fiber.
It’s no secret that outside-plant (OSP) fiber construction is expensive. Construction costs vary, but they are always hefty, and they increase greatly if cable is buried. In addition to construction, the costs of permitting, zoning, raw materials and splicing are significant. Thus, avoiding installing new fiber is best whenever possible.
Many communications providers are experiencing fiber exhaust in their networks. This means that the cable counts initially deployed are not able to handle today’s needs. Now, emerging technologies in cell backhaul, business class services and others are creating a need for yet more fibers. However, in most cases, ever-increasing labor and material prices make new fiber construction too costly to consider for many projects.
WDM allows operators to place new equipment at either end of a fiber strand and combine multiple wavelength channels on a single fiber strand. Many existing systems use only a small amount of the spectrum available on single piece of glass. Using either coarse wave-division multiplexing (CWDM) or dense wave-division multiplexing (DWDM), operators can combine many different services on a single fiber by assigning a different color, or wavelength, to each service. Multiplexers are used to combine all these wavelengths onto a single fiber, and demultiplexers are used to separate the colors farther on in the network.
Mobile devices, cloud computing, over-the-top video, DOCSIS 3.1 with IPTV, and online gaming are just a few of the drivers for increased bandwidth demand. As demand continues to rise, service providers will need long-term strategies to develop a bigger pipe.
Cellular backhaul, FTTx and commercial business services are also creating a need for more fiber capacity. 3G and 4G cellular services require more bandwidth than cellular services needed in years past and therefore require a fiber link to each cell site. A provider may own a fiber sheath that runs right past a cell tower, but all its fibers may currently be used to maximum capacity. Providing lit services or dark fiber to cell towers can be very profitable but not if it requires plowing or hanging new fiber to these cell sites.
Business-class services are becoming popular revenue sources for communications companies. Businesses are often willing to sign long-term contracts and pay more than residential customers. In some cases, businesses require fiber to meet their bandwidth needs. The same issue arises here: How is it possible to serve these new customers without having to install new OSP fiber to those sites?
Most legacy fiber networks use a single wavelength, or color, on each fiber. Think of it as two people on different mountaintops using white-lens flashlights to communicate via Morse code – not very sophisticated, but it works.
All of a sudden, two more people want to start communicating between those two mountaintops. What is the solution? Use different colored lenses on the flashlights to communicate. Senders and receivers will recognize and send only their own colors of light and ignore the others.
This is basically what a WDM network does. It uses multiple colors of light over the same medium (fiber). Transmitters tuned to specific wavelengths send light into a passive combiner called a mux (short for multiplexer). All the wavelengths travel down the common fiber and are separated using a passive demultiplexer (also called a demux). Now each receiver at the other end will be able to receive just its own discrete signal.
In other words, WDM maps multiple optical signals to individual wavelengths and multiplexes the wavelengths over a single fiber. WDM can carry multiple protocols without having to convert them to a common signal format. A single fiber is able to do virtually anything that’s needed.
There are two main types of WDMs. The advantage of CWDM technology is that it is relatively inexpensive compared with DWDM. The transmitters used in CWDM are less expensive, as they do not need to be tuned as precisely as DWDM transmitters. However, CWDM has drawbacks, too: Only 18 channels are available, and fiber amplifiers cannot be used with them. Thus, they are not the ideal choice for long-haul networks.
CWDM channels each consume 20 nm of space and together use up most of the single-mode operating range. The wavelengths most commonly used are the eight channels in the 1470 to 1610 nm range. Any transceiver used in CWDM applications operates within one of these channels.
DWDM allows many more wavelengths to be combined onto one fiber. It also leverages the capabilities of fiber amplifiers, which can amplify the 1550 nm or C band commonly used in DWDM applications. This makes it ideal for use in long haul and areas of greater customer density. Instead of the 20 nm spacing in CWDM (equivalent to about 15 million GHz), DWDM uses either 50, 100 or 200 GHz spacing in the C and sometimes the L bands. This allows many more wavelengths to be packed onto the same fiber.
The downside of DWDM is that the lasers need to be much more accurate and require precise temperature ranges to operate. This makes DWDM applications much more expensive than CWDMs. The introduction of the ITU-T G.694.1 grid in 2002 made integrating DWDM technology easier. It created an industry standard for DWDM.
Before deploying any WDM equipment, it is necessary to ensure that the glass in place will support all the required wavelengths. Low-water-peak or zero-water-peak fiber is more suitable for WDM applications, and older glass types may have water peak issues. If the glass is too old, it may be necessary to bite the bullet and install some new fiber.
Assuming the glass is appropriate for WDM, should you use CWDM or DWDM technology to solve fiber exhaust problems? As previously noted, CWDM can support a maximum of 18 channels and is not ideal for long haul. So CWDM would typically be best for applications that do not require the signal to travel great distances and in locations where not many channels are required. The availability of SFP transceivers may also be a limiting factor.
For applications that require a high number of channels or for long-haul applications, DWDM is the ideal solution. Though the electronics and passives are not cheap, they are considerably more cost-effective than putting in new fiber.
It’s important to ensure that the CWDM and DWDM passives will operate properly in the environment where they will be placed. This becomes especially important when putting CWDM passives in the outside plant. Before buying a mux or demux for use in an unconditioned cabinet or splice case, verify that the operating temperature will fit the application. Many vendors specify the storage temperature but not the operating temperature.
The operating temperature of an optical component is the actual temperature range in which the component will work. Usually, a component must remain within a specified temperature range to perform at a specified optical performance level.
The storage temperature of an optical component is the temperature at which an optical component can be stored without causing any degradation or component failure when it is used in the component’s specified operating temperature limits. Some storage temperatures can exceed the actual operating temperature of the components. When sourcing WDM filters, ensure that they will be able to operate within the temperatures in which they will be deployed.
Another design consideration with any WDM network is insertion loss. Though WDM creates a huge increase in capacity, it also creates insertion loss in a network. Using the maximum insertion loss values in the link budget is a good idea; keep in mind that some manufacturers do not include the connector loss if the device is terminated.
Calculate the loss for both the mux and demux components. The maximum insertion loss on a typical eight-channel CWDM is 3 dB, so for a mux/demux solution, add 6 dB of insertion loss.
WDM filters can be designed to drop individual colors at a specific location and keep sending the rest down the fiber path. In some applications, combining several wavelengths at a certain location and then dropping individual channels to customers along the same route may be desirable. This is the most common type of design used in fiber-to-the business and cell tower applications.
WDM technology is a very effective method for overcoming fiber exhaust. Placing passive filters and WDM transceivers at each end of a fiber optic network can greatly increase bandwidth without having to spend capital on new fiber construction projects. Most current fiber technologies use only a small sliver of the available bandwidth capacity of single-mode glass, so a properly designed WDM network can unlock a floodgate of available power in a network. Using many channels on the same piece of optical fiber enables operators to serve businesses, cell towers and residential customers with the same fiber. Fiber counts are no longer a constraint.


WDM technology can be a reliable, cost-effective method of solving fiber exhaust problems and expanding bandwidth across campuses, municipalities, school districts, and other networks. In our first installment, we covered the basics behind the technology and how it works. In this installment, we will discuss how to begin deciding which WDM is right for you, as well as addressing some common misconceptions about this incredibly valuable technology.
Deciding between CWDM and DWDM is a complex issue, with many network- and application-specific variables that need to be considered. While we recommend a consultation with an expert to get a definitive answer, here are some preliminary considerations:
Common Misconception 1: WDM is extremely expensive to install.
For many network operators, the concept of “WDM” is inextricably linked with large, complex active line systems that cost hundreds of thousands of dollars. For most applications, this is a case of upselling by their OEMs. In fact, you can reap many of the benefits much more cost-effectively with a passive filter system. Passive CWDM and DWDM systems can be monitored via a tap port on the faceplate of most mux/demuxes.
Common Misconception 2: WDM can only cover long distances.
Network operators are often discouraged from adopting passive WDM system because the rated distances of the transceivers are much longer than required. For example, the shortest rated distance for CWDM transceivers is 40km, and 80km for DWDM transceivers. Is it still possible to use these optics if your campus is only, say, 8km, or even 100m apart?
The answer is yes! With the proper level of attenuation on the transmitting side of your transceivers, you can still deploy a passive WDM solution to add services and conserve fiber.
Further Reading
For more information about different WDM strategies and how to use them, you can check out our coverage on our ZS line of standard passives, this application note on some simple passive architectures, and an overview WDM strategies using a single strand of common fiber.
You can also schedule a consultation with our experts, who will walk you through your options step by step and find the perfect solution for your network.

Details of the differences between fiber-optic network cards and HBA cards

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In the early SAN storage system, the server and the switch data transmission is through the fiber, because the server is the SCSI instruction to the storage device, can not take the ordinary LAN network IP protocol, so the need to use FC transmission, so this SAN is called FC-SAN, and later appeared in the IP protocol package SAN, can take the ordinary LAN network, so called IP-SAN, the most typical of which is now popular ISCSI.
Details of the differences between fiber-optic network cards and HBA cards
These two methods need to be heavy on the data block package unpacking operation, so the high-performance SAN system is the need to install a dedicated server on the unpacking work to reduce the burden on the processor card, this card we called It can provide a fiber interface (if it is an iSCSI HBA card is to provide a common RJ45 interface) for the corresponding switch connection; In addition, the HBA physical you can put it as NIC or PCI-E slot, so the use of this device is very a network card, many people also put it with ordinary network card or ordinary fiber-optic network card confused. Of course, some iSCSI HBA card can be used as a normal network card, but from the price to consider this is very extravagant.
The general definition of the HBA is the I / O adapter that connects the host I / O bus and the computer’s memory system. According to this definition, like the video card is connected to the video bus and memory, the network card is connected to the network bus and memory, SCSI-FC card is connected to SCSI or FC bus and memory, they should be regarded as HBA. HBA cards have FC-HBA and iSCSI HBA in the future there are other HBA cards, but HBA is usually used in SCSI. Adapter and NIC for FC; NICs are also used for Ethernet and Token Ring networks.
In fact, the network card is often referred to as a type of equipment in general, refers to the installation in the host, through the network cable (twisted pair, fiber optic cable, coaxial cable, etc.) and network switches (Ethernet switches, FC switches , ISCSI switches, etc.), or with other network devices (storage devices, servers, workstations, etc.) to form a network of hardware devices.
So, what is the name of the fiber-optic network card in the end refers to the fiber port HBA card?
In fact, we often say that the fiber-optic network card refers to the fiber channel network HBA card.
Due to the different transmission protocols, the card can be divided into three, one Ethernet card, the second is the FC card, the third is the iSCSI card.
• Ethernet card: The name of the Ethernet Adapter, the transmission protocol for the IP protocol, generally through the fiber optic cable or twisted pair and Ethernet switch connection. The interface type is divided into optical port and electrical port. Optical interface is generally through the fiber optic cable for data transmission, the interface module is generally SFP (transmission rate 2Gb / s) and GBIC (1Gb / s), the corresponding interface for the SC, ST and LC. The current interface type is RJ45, used to connect with the twisted pair, but also with the coaxial cable connection interface, but now has been used less.
• FC card: generally also called fiber optic card, scientific name Fibre Channel HBA. The transport protocol is a Fiber Channel protocol and is typically connected to a Fiber Channel switch through a fiber optic cable. The interface type is divided into optical port and electrical port. Optical interface is generally through the fiber optic cable for data transmission, the interface module is generally SFP (transmission rate 2Gb / s) and GBIC (1Gb / s), the corresponding interface for the SC and LC. The interface type of the electrical interface is generally DB9 pin or HSSDC.
• ISCSI NIC: The ISCSI HBA, which transmits the ISCSI protocol, has the same interface type as the Ethernet card.
Fiber-optic network card” generally refers to the FC HBA card, plug in the server, external storage with the fiber switch; and optical Ethernet card is generally called “fiber Ethernet card” is also inserted in the server, but it is an external Optical Ethernet switch.

Optical module selection and use of skills

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The optical module is composed of optoelectronic devices, functional circuits and optical interfaces. The optoelectronic devices include two parts: transmit and receive. Optical module can be photoelectric conversion, the transmitter side of the electrical signal into optical signals, and then transmitted through the optical fiber at the receiver and then converted into electrical signals. Any one optical module is a two-part function of the transceiver, photoelectric conversion and electro-optical conversion, so that both ends of the network equipment are inseparable from the optical module. Now a data center equipment is often million, in order to achieve the interconnection of these devices, optical modules indispensable. Today, optical modules have become a segment of the data center.
With the wide range of optical modules, more and more customers are concerned about the stability of the module itself and the characteristics of reliability. There are three popular optical modules on the market: original optical modules, second-hand optical modules and compatible optical modules. As we all know, the price of the original optical module is very high, many manufacturers can only discourage. As for the second-hand optical module, although its price is relatively low, but the quality is not guaranteed, often in the use of six months after the phenomenon of packet loss. As a result, many vendors have turned their attention to compatible optical modules. Indeed, compatible with the optical module in use, its performance and almost no original optical module, and the price is much cheaper than the original optical module several times, which is compatible with the optical module can be hot reasons. However, the goods on the market varies greatly, many businesses have shoddy, fish, the selection of the optical module caused a certain degree of difficulty, the following slim talk about the choice of optical modules.
First of all, the first question, how do we distinguish between new optical modules and second-hand optical modules? We mentioned above, second-hand optical module is often used in the use of six months after the packet loss, this is because of its optical power instability and decreased light sensitivity and other reasons. If we have an optical power meter, you can come up with a test to see if its optical power is consistent with the parameters on the data sheet. If the access is too large, the second-hand optical module.
And then observe the use of optical modules after sale. The life of a normal optical module is five years, and it is difficult to see the light module in the first year, but it can be seen in the second or third year of its use.
Second, see how the compatibility between the optical module and the device. Consumers before the purchase, the need to communicate with suppliers, inform them need to use in which brand of equipment.
Finally, we also need to see how the temperature module to adapt to the temperature. Optical module itself in the work of the temperature is not high, but it is the general working environment in the engine room or on the switch, the temperature is too high or too low will affect its optical power, light sensitivity and other parameters. In general, the optical module used in the temperature range of 0 ~ 70 ° C can, if in a very cold or extremely hot environment, you need to use industrial-grade -40 ~ 85 ° C optical module.
The use of optical modules
If the use of the process, found that the optical module function failure, first do not worry, to carefully check, analyze the specific reasons. General optical module function failure there are two, respectively, for the transmitter failure and receiver failure. The most common causes are mainly:
Optical module optical port exposed to the environment, the light port into the dust and pollution;
The use of fiber optic connector end has been contaminated, optical module secondary pollution port;
With the pigtail of the optical connector end use improper, end scratches and so on;
Use inferior fiber optic connectors.
Therefore, the correct purchase of optical modules, usually in use, but also pay attention to the optical module cleaning and protection. After the use of the usual use, it is recommended not to use when the plug on the dust plug. Because if the light contact is not clean, it may affect the signal quality, may lead to LINK problems and error problems.

FAQ of 40G wiring and XFP module

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40G network is more and more popular nowadays. Know the information about 40G optical transceiver module is important for you to deploy 40G Ethernet.
Question: what is the maximum transmission distance supported by 40GbE?
Answer: IEEE 40GBASE-X standard is described as follows:
40GBASE-SR4 transmission distance is 100m when using OM3 multimode fiber, can up to 150m when using OM4 multimode fiber. OM1 and OM2 transmission is not supported. 40GBASE-LR4 transmission distance is 10KM single mode fiber(Same fiber can be used in 10G single mode 10GBASE-LR standards). 40GBASE-CR4 supports a maximum transmission distance of 7 meters. However, due to the limitation of copper technology, may not be able to reach its maximum transmission distance. 40GBASE-KR4 supports backplane technology, transmission distance is 1 meters.
Question: Can 40G-LR4 optical modules be split into 4x10G connections?
Answer: No, 40G-LR4 module can not be divided into 4x10G. 40GBASE-LR4 uses 4 lambda (or wavelength) on a pair of single-mode fibers, and it doesn’t automatically divide itself into 4 pairs, unless the wavelength can be split. The uniqueness of 40GBASE-SR4 lies in its use of parallel optical fibers and allows simultaneous use of 4 pairs of parallel optical fibers. Both 40G-PLRL4 and 40G-PLR4 standards support 4x10G, using 12 core single-mode MTP ribbon fiber, and all of them can achieve the maximum transmission distance.
Question: What is the standard transmission performance of 40GbE PLRL4?
Answer: 40G parallel LR4 Lite (PLRL4) 10GBASE-LRL standard, the transmission distance is 1KM when using single-mode fiber. In addition, 40GbE PLRL4 optical devices connect the branch cables or single mode fiber boxes by using the 4x10G mode, can support 4 independent 10G-LR connections.
Question: What types of fiber are needed for PLRL4 and PLR4 optical modules?
Answer: PLR4 and PLRL4 use a 12 core MTP fiber connector, and require a APC single-mode 12 core MTP fiber. The fiber is equivalent to a 40G-SR4 MTP-MTP, the only change is the former uses single-mode optical fibers. UPC optical connector is another type of 12 core MTP connector, but it is not suitable for single-mode optical fiber. APC is the only viable choice for single-mode 12 core MTP fibers.
QSFP+ to QSFP+ and QSFP+ to 4SFP+ copper cable can achieve short distance connection, and for long distance connection, Fiberland provides a full range of optical transceivers, to meet the needs of various optical fiber type and distance.

How to choose the MPO system for your Fiber Infrastructure

Nowadays, the demand for high connection speeds is increasing at an intimidating pace. People need to send -and receive- more data than ever, and the technology that’s available to them often seems to just not being able to keep up.
Optical fiber seems to represent the best choice when it comes to offering higher speeds -currently required by data center networks. In contrast to multimode and single mode optical networks, which were typically based on duplex fiber links, parallel fiber (MPO-based) connectivity has now become the ideal go-to choice, since it allows the use of pre-terminated systems that can be used in a quick and efficient way.
Nonetheless, this type of connectivity had been used to deliver duplex connectivity combined with duplex modules and breakouts. The selection of multifiber interfaces responds to the demands of increasing applications and density.
This turnover has led to a general consideration of using duplex connectivity, but at the same time, it needs to fill the necessity of including a combination of parallel and duplex interfaces.
Apart from considering these new iterations, it is essential to have a solid grasp on the evolution of network equipment and on the advantages of implementing an infrastructure based on duplex connections.
That being said, let us walk you through the Ethernet Roadmap.
There are several applications housed in data centers, which implies that those applications will demand a diversity in the connectivity topologies. It is commonly known that most networks use duplex links, but the demand for higher speeds requires using duplex links into other groups of links, which is when the term of parallel links enter the debate.
Likewise, this new incorporation asks for certain cabling structures that can handle this new array of options while having the acute vision of what the new results from this structures may provide us with. In other words, what we’re now witnessing it’s a migration from arrangements that involve duplex links into parallel link options that need to cover the requirements of higher speeds.
The great thing about parallel links is that they reduce the operation costs at a significant rate. Since they offer higher connectivity densities, it reduces the power consumption to send that data. This type of connection multiplies the information been transported, so it offers a notable reduction in the time employed in the transmission of information.
The increase of speeds has also developed a certain progress when it comes to the outlining of separate transmission lanes. In the end, the throughput will be augmented due to the incorporation of additional fiber, or the multiplexing over just a single a fiber.
Each one of these parameters will determine the selection of the fiber media and the options for cabling that will become the most appropriate for your data center. The decision of moving from single and duplex links to parallel ones will surely affect your cabling choice. This may traduce to a significant cost at the beginning, but it shall be seen as an investment in the long term.
The first thing you need to do is to determine the desired capacity that your data center will possess in the short-term future. Your team can come in handy forecasting this scenario since it is very well equipped with considering, evaluating and even trying several technologies, platforms and routing strategies.
After coming to terms to answering each one of the specific requirements demanded by your new system, the pre-terminated MPO-based fiber cabling system will enable a quicker utilisation and a certain flexibility of configuration, along with a cabling topology that corresponds appropriately with the new direction and desired performance of your data center direction.
Multimode fiber is definitely the primary media choice for the enterprise data center. Each one of the diverse types of multimode fiber (MMF) will affect the scale and scope of the data center that can be supported when speeds increase, so you need to take that into consideration.
Aside from combining “lanes” to provide for higher and better link speeds, multiplexing several wavelengths on a single pair of fibers offers great results.
The great thing about this new structure of links is that it offers a new set of applications. Depending on the type of configuration, migrations can be enabled between duplex and parallel optics.
This quality is very eloquent when it comes to supporting the notion of the flexibility offered by parallel links. If new needs come up, you should be able to accommodate those necessities by making adjustments to your new structure in your data center.
Every decision that you make towards implementing parallel links will affect your structure -and space- of your cabling, so every single analysis that you can make before adding something to your new structure should be mandatory.
To put it mildly, you need to be aware of the physical space every new configuration is going to occupy. You can have lots of great ideas for new connections, but if you can’t afford the space for it, none of them will work out. But don’t worry, you just need to gain conscience of the dimensions of your cabling configurations so you can design them and implement them properly.
The good thing about duplex cables is that they are very flexible, so not all of these considerations should be thought of as limitations. You can work around them -and, trust us, you should!
By merely thinking about all of this, you could be concerned about the cost it implies, and we hear you. Notwithstanding, this is a cost you need to assume. Not only because the current situation demands it, but also because this decision will stand out as an investment for the near future.
New designs imply adjustments so you can incorporate duplex and parallel connections, meaning that perhaps new racks or more space for your cabling will be needed. This inclusion will also call for changes in the management of your team, which will have to face new ways to handle these devices.
Human beings tend to reject at first all sorts of changes, it’s in our nature, but if you are totally convinced on the benefits that each and single one of these procedures will bring to your data center in the future, you will work through them focused on having the vision aiming at an impending success. The current concerns need to be replaced with a relentless optimism that your work will be enhanced in the long run.
We hope you find this article very useful and that this information can help you increase the speed -and hopefully the quality- of your data center.