Passive DWDM vs. Active DWDM

To keep pace with the rapidly growing volumes of data-network traffic driven by the growth of the Internet, service providers are always looking to increase the fiber capacity and wavelength spectral efficiency in their networks. DWDW (dense wavelength division multiplexing) is an optical multiplexing technology used to increase bandwidth over existing fiber networks. DWDM works by combining and transmitting multiple signals simultaneously at different wavelengths on the same fiber. It has revolutionized the transmission of information over long distances. DWDM can be divided into passive DWDM and active DWDM which will be illustrated in this article.

Passive DWDM

“Passive” refers to the passive DWDM MUX/DEMUX element which is an unpowered, pure optical equipment. Passive DWDM systems have no active components, which means that no optical signal amplifiers and dispersion compensation modules (DCM) are used. The DWDM passive link is only determined by the optical budget of transceivers used. Passive DWDM system has a high channel capacity and potential for expansion, but the transmission distance is limited to the optical transceivers used. The main application of passive DWDM system is metro networks and high speed communication lines with a high channel capacity.

Active DWDM

Active DWDM system is built from transponders, providing full optical demarcation point agnostic to the routers, switches and ADMs within the network. Active DWDM offers a way to transport large amounts of data between sites in a data center interconnect setting. The transponder takes the outputs of the SAN or IP switch format, usually in a short wave 850nm or long wave 1310nm format, and converts them through an optical-electrical-optical (OEO) DWDM conversion. In long-haul DWDM networks, several EDFAs are installed sequentially in the line. The number of amplifiers in one section is determined by the fiber cable type, channel count, data transmission rate of each channel, and permissible OSNR value.

Besides, the maximum transmission distance of the active DWDM system also depends on the influence of chromatic dispersion—the distortion of transmitted signal impulses. When designing a DWDM network project, permissible values of chromatic dispersion for the transceivers should be considered, and, if necessary, chromatic dispersion compensation modules are included in the line. DCM fixes the form of optical signals that are deformed by chromatic dispersion and compensates for chromatic dispersion in fibers.

Passive DWDM vs. Active DWDM

Choosing passive or active DWDM system depends on your requirements and current setup. Because both of them have pros and cons.

Passive DWDM
Pros:
1. Inexpensive – As mentioned above, less components are required, and less engineering time is required.

2. INITIAL Setup – Because of the colored optics there isn’t a need to tune wavelengths for all of your connections. It’s a matter of matching your colored optics and plugging it.

Cons:
1. Scalability – you are limited to colored optics, and less wavelengths on the transport fiber. As you grow, you would be required to have more passive devices. Furthermore, with the more passive devices, you have more difficulty to manage. And you will have to start managing the same wavelength on multiple passive devices and they could be serving different purposes on each depending on your setup.

2. Control – If you need to change a wavelength or connection for whatever reason, your option is limited to taking it out of service and disconnecting the physical cabling as the wavelength is tied to the optic.

Active DWDM
Pros:

1. Active can fit a lot more wavelengths (colors) onto a single fiber pair. The composite signal that is sent over a single fiber pair can carry more bandwidth than a passive of the same size, in turn you don’t need as much physical fiber between your two sites (this really only applies if you require that much bandwidth). This is advantageous when distance is a problem because it allows you to get more out of a single leased fiber pair as opposed to passive.

2. Active setups grant you more control over your optical network, you can dynamically re-tune wavelengths without dropping connections (it’s transparent to whatever is riding on that wavelength).

3. Scalability – Active can be easier to scale as your network grows (you can fit more wavelengths on the fiber, see above), but again – we’re talking seriously big iron. I’ll dig into it a bit more below.

Cons:
1. EXPENSIVE – Active DWDM setups are much more expensive compared to passive DWDM. If you don’t have long-distance requirements, don’t choose active DWDM.

2. Configuration – Depending on your vendor, configuration can be a serious undertaking, and require a solid understanding of optical networks. There are many more components in active builds.

Conclusion

Most of the time, DWDM operates with powered component like transponders. Further, after multiplexing the signals, they typically need active amplification to have any preferred reach. Without this, you’re only going with a relatively short distance, which is not a good value for the expense of DWDM.

Installation Guide to CWDM MUX/DEMUX System

CWDM MUX/DEMUX System Overview

Coarse Wavelength Division Multiplexing (CWDM) is a wavelength multiplexing technology for access networks. It is designed to increase fiber optic network capacity without adding additional fibers. The wavelengths of CWDM channels range from 1270nm to 1610nm with 20nm spacing, which allows the use of cost-effective lasers. CWDM MUX/DEMUX system is a passive, optical solution to increase the flexibility and capacity of existing fiber lines in high-speed networks. By adding more channels into available fibers, the CWDM MUX/DEMUX system enables greater versatility for data communications in ring, point-to-point, and multipoint topologies for both enterprise and metro applications.

CWDM MUX/DEMUX System Components

All CWDM system components are passive and require no power supplies. They consist of the rack mount chassis, a set of CWDM MUX/DEMUX and CWDM OADM (Optical Add/Drop Multiplexing) modules with color-coded ports. The CWDM MUX/DEMUX takes 4 or 8 different wavelength channels and multiplexes them onto one common fiber cable for transmission to the network. Then it demultiplexes the channels it receives from the network and sends each channel to a different device. Multiple modules may be chained through the expansion port on the four-channel modules. Thus it increases flexibility and enables growth for evolving networks.

The CWDM OADM module can add or drop CWDM channels into an existing backbone ring. It provides the ability to drop one CWDM channel from the network fiber, while allowing all other channels to continue pass to other nodes. Similarly, the drop/insert module removes an individual channel from the network fiber, however, it also provides the ability to add that same channel back onto the network fiber. The drop/insert module supports two paths (east and west) for dropping and adding, so that network viability is maintained in a ring topology, even if a break occurs in the ring.

CWDM MUX/DEMUX System Installation Guide

Step1: Mount the system chassis on the rack. The CWDM rack-mount chassis can be mounted in a standard 19-inch cabinet or rack. Make sure that you install the rack-mount chassis in the same rack or an adjacent rack to your system so that you can connect all the cables between your CWDM MUX/DEMUX modules and the CWDM SFP transceivers.

Step2: Install the CWDM MUX/DEMUX modules. First loose the captive screws on the blank of module panel and remove the panel. Then align the module with the slot of the chassis shelf and gently push the module into the slot. Finally, ensure that you line up the captive screws on the module with the screw holes on the shelf and tighten them up.

Step3: Install CWDM SFP transceivers. Since each channel has a specific wavelength, transceivers must comply with the right wavelengths. Each wavelength must not appear more than once in the system. Device pairs must carry transceivers with the same wavelength.

Step4: Install the CWDM MUX/DEMUX to the switch. After inserting the CWDM SFP transceiver into the switch, single-mode patch cables are used to connect the transceiver to the CWDM MUX/DEMUX module.

Step5: Connect the CWDM MUX/DEMUX pairs. In a CWDM MUX/DEMUX system, multiplexer and demultiplexer must work in pairs. Two strands of single-mode patch cables are needed in the duplex MUX/DEMUX module and one strand for the simplex one. Simply insert single-mode cables from your system equipment to the appropriate port on the CWDM MUX/DEMUX or OADM module.

Conclusion

CWDM MUX/DEMUX system is an attractive solution for carriers who need to upgrade their networks to accommodate current or future traffic needs while minimizing the use of valuable fiber strands. With CWDM technology, you can accommodate Ethernet and SONET on a single fiber that enables converged circuit/packet networks at high demand access sites. Besides, CWDM MUX/DEMUX can work seamlessly with transceivers to optimize link length, signal integrity and network cost, thus becoming a single rack-mount solution for enhanced design, power and space efficiency.

 Source: http://www.china-cable-suppliers.com/

Identify Various Ports on WDM Mux/Demux

In today’s world of intensive communication needs and requirements, fiber optic cabling has become increasingly popular. But considering the physical fiber optic cabling is expensive to implement for each individual service, using a Wavelength Division Multiplexing (WDM) for expanding the capacity of the fiber to carry multiple client interfaces is a highly advisable. WDM MUX/DEMUX (Multiplexer/De-Multiplexer) is one of the most important components in WDM systems. But there are so many types of ports which are not so easy to identify. This article will illustrate various ports with different functions on WDM Mux/Demux.

Common Ports on WDM Mux/Demux

For WDM Mux/Demux, channel port and line port are the most common and necessary ports for normal operation of the WDM Mux/Demux.

Channel Port
CWDM uses 18 wavelengths ranging from 1270nm to 1610nm with channel intervals of 20nm. Channel ports on CWDM MUX/DEMUX is usually ranging from 2 to 18. DWDM uses the wavelength ranging from 1470nm to 1625nm usually with the channel port ranging from 4 to 96. Since DWDM Mux/Demux has a more dense channel spacing of 0.8 nm (100 GHz) or 0.4 nm (50 GHz), it is more suitable for high-density networks.

Line Port
There are two types of line port available for CWDM and DWDM MUX/DEMUX. One is dual fiber line port, and the other is single fiber line port. The wavelengths order and the applications of them are totally different. Dual-fiber line port is used for bidirectional transmission, which means the TX port and RX port of every duplex channel port supporting the same wavelength. The WDM MUX/DEMUXs with dual fiber line ports installed on the two ends of the network could be the same. Single-fiber line port only support one direction data flow. If you choose a single-fiber WDM MUX/DEMUX on one side of the network, there should be a single-fiber WDM MUX/DEMUX which supports the same wavelengths but has the reverse order on the TX port and RX port of every duplex channel port.

Special Ports on WDM Mux/Demux

1310nm Port and 1550nm Port
1310nm and 1550nm ports are wavelength ports of WDM MUX/DEMUX. Since a lot of optical transceivers use these two wavelengths for long-haul network, adding these two ports when the device does not include these wavelengths is very important. CWDM Mux/Demux can add either type of wavelength ports, but the wavelengths which are 0 to 40 nm higher or lower than 1310 nm or 1550 nm cannot be added to the device. However, DWDM Mux/Demux can only add 1310nm port.

Expansion Port
Expansion port which can be added on both CWDM and DWDM Mux/Demux is a special port to increase the number of available channels carried in the network. It means that when a WDM Mux/Demux can not meet all the wavelength needs, it is necessary to use the expansion port to add different wavelengths by connecting to another WDM Mux/Demux’s line port.

Monitor Port
This port is used to monitor or test the power signal coming out of a Muxed CWDM or before it gets demuxed from the signal coming through the fiber network usually at a 5% or less power level. Generally, it can be connected with measurement or monitoring equipment, such as power meters or network analyzers.

No matter the common ports or the special ports on WDM Mux/Demux have their own features and application. FS.COM WDM products designed for easy and fast implementation take up minimal space and use least power, thus providing the highest integration level of CWDM and DWDM networks. They can also provide complete solutions for CWDM and DWDM. Kindly contact sales@fs.com for more details if you are interested.

Why Is Fiber Optic Technology ‘Faster’ than Copper?

The deployment of fiber optics in telecommunications and wide area networking has been common for many years, but more recently fiber optics have become increasingly prevalent in industrial data communications systems as well. Fiber optic technology uses pulses of light to carry data along strands of glass or plastic. It’s the technology of choice for the government’s National Broadband Network (NBN) and data centers, which promises to deliver next-generation 200G and 400G Ethernet speeds.

When talking about ‘speed’, we were actually talking about throughput (or capacity) — the amount of data you can transfer per unit time, says Associate Professor Robert Malaney from the University of New South Wales, School of Electrical Engineering and Telecommunications.

And fiber optics can definitely transfer more data at higher throughput over longer distances than copper wire. For example, a local area network using modern copper lines can carry 3000 telephone calls all at once, while a similar system using fiber optics can carry over 31,000.

So what gives it the technical edge over copper wires? Traditional copper wires transmit electrical currents, while fiber optic technology sends pulses of light generated by a light emitting diode or laser along optical fibers.

In both cases you’re detecting changes in energy, and that’s how you encode data. With copper wires you’re looking at changes in the electromagnetic field, the intensity of that field and perhaps the phase of the wave being sent down a wire. With fiber optics, a transmitter converts electronic information into pulses of light — a pulse equates to a one, while no pulse is zero. When the signal reaches the other end, an optical receiver converts the light signal back into electronic information.

The throughput of the data is determined by the frequency range that a cable will carry — the higher the frequency range, the greater the bandwidth and the more data that can be put through per unit time. And this is the key difference — fiber optic cables have much higher bandwidths than copper cables (eg. cat5e copper cable).

“Optical fiber can carry much higher frequency ranges — note that light is a very high frequency signal — while copper wire attenuates or loses signal strength at higher frequencies,” says Malaney.

Also, fiber optic technology is far less susceptible to noise and electromagnetic interference than electricity along a copper wire.

“You can send the signal for over 200 km without any real loss of quality while a copper cable signal suffers a lot of degradation over that distance,” says Malaney.

As well as a significant increase in connection speed, fiber optic networks offer a tremendous capacity to keep up with any new technological advances. Once the basic fiber optic infrastructure is in place, it can be rearranged and the end point electronics upgraded when necessary, to deliver even higher capacity. It can do this far more effectively than existing wireless or copper based systems.

In terms of its serviceable lifetime, glass (from which fiber optic cable is made) is long lasting, stronger than copper and more able to retain its transmission properties after physical stress such as weight strain, or even attack by rats and cockatoos. We install fiber differently from copper: in good quality coatings, inside ducts, or in the case of newer systems, encased entirely by electrical transmission wires.

For applications where signal security is a concern, fiber optic technology is an excellent solution. Fiber optic cables do not generate electromagnetic fields that could be picked up by external sensors. It is also more difficult to ‘steal’ signals by spicing into optical fibers than it might be with conventional copper wiring.

Shielded vs. Unshielded Twisted-Pair Cable

As we all know, the advantages and disadvantages of shielded and unshielded twisted-pair cable are under debate for a long time. Advocates of STP cable, which includes screened twisted-pair and foil twisted-pair cables, claim that it is superior to UTP cable. Shielded versus unshielded twisted-pair cable, which is the winner? This post will give you the answer.

STP and UTP cable differ in design and manufacture. But their purpose should be the same–to provide reliable connectivity of electronic equipment. In theory, both types of cable should do this equally well. The true test comes when you look at how each of these cable types performs that task within its respective end-to-end system.

Shielded Twisted-Pair Cable

Shielded twisted-pair cable encases the signal-carrying wires in a conducting shield as a means of reducing the potential for electromagnetic interference. How effective the shielding is depends on the material used for the shield–its thickness and frequency, the type of electromagnetic noise field, the distance from the noise source to the shield, any shield discontinuity and the grounding practices. Also, crosstalk and signal noise can increase if the effects of the shield are not compensated for.

Some STP cables, for example, use a thick braided shield that makes a cable heavier, thicker and more difficult to install than its UTP counterpart. Other STP cables use only a thin outer foil shield. These cables, known as screened twisted-pair cables or foil twisted-pair cables, are thinner and less expensive than braided STP cable; however, they are not any easier to install. Unless the minimum bend radius and maximum pulling tension are rigidly observed when these cables are installed, the shield can be torn.

Unshielded Twisted-Pair Cable

Unshielded twisted-pair cable does not rely on physical shielding to block interference. It relies instead on balancing and filtering techniques using media filters, baluns or both. Noise is induced equally on two conductors and is canceled out at the receiver. With properly designed, manufactured and installed UTP cable (like CAT6 UTP cable), the network is easier to maintain than one in an STP cable plant, with its shielding continuity and grounding issues.

UTP cable has evolved during the years, and different types are available for different needs. Basic telephone cable, also known as direct-inside wire, is still available. Improvements over the years–variations in the twists or in individual wire sheaths or overall cable jackets–have led to the development of Cat3 cable that is compliant with the Electronic Industries Association/ Telecommunications Industry Association-568 standard for transmission rates up to 16 megahertz. Cat 4 UTP cable is specified for signal bandwidths to 20 MHz, and Cat5e UTP cable for specifications to 100 MHz–and possibly higher.

Shielded vs. Unshielded Twisted-Pair Cable

Since UTP cable is lightweight, thin and flexible, as well as versatile, reliable and inexpensive, millions of nodes have been, and continue to be, wired with this cabling medium. This is especially true for high-data-rate applications. For best performance, this UTP cable should be used as part of a well-engineered structured cabling system.

If STP cable is combined with improperly shielded connectors, connecting hardware or outlets, or if the foil shield itself is damaged, overall signal quality will be degraded. This, in turn, can result in degraded emission and immunity performance. Therefore, for a shielded cabling system to totally reduce interference, every component within that system must be fully and seamlessly shielded, as well as properly installed and maintained.

An STP cabling system also requires good grounding and earthing practices because of the presence of the shield. An improperly grounded system can be a primary source of emissions and interference. Whether this ground is at one end or both ends of the cable run depends on the frequency at which a given application is running. For high-frequency signals, an STP cabling system must be grounded, at minimum, at both ends of the cable run, and it must be continuous. A shield grounded at only one end is not effective against magnetic-field interference.

The length of the ground conductor itself can also cause problems. If it is too long, it no longer acts as a ground. Therefore, because specific grounding requirements depend on the application, a general grounding policy that ensures the best results for an STP cabling system is not possible.

UTP cabling doesn’t have this problem. While an STP cabling system is dependent on such factors as physical continuity of the cable shield or installation with adequately shielded and grounded components, a UTP cabling system inherently has fewer potential trouble spots and is much easier to install.

Straight-Through vs. Crossover Ethernet Cables

Ethernet cables or networks cables are used for data transmission between devices on a network. They consist of a copper cable with 4 pairs of wires and connected by RJ45 connectors on each end of the cable. Most Ethernet cables in use today are either Cat5e and Cat6 which offer higher data transfer rates than the older types such as Cat5 and Cat4. Although various types of Ethernet cables look the same, the internal wiring distinguishes. Ethernet cables can come in two different wiring applications: straight-through and crossover, each of them with different wire arrangement in the cable for serving different purposes.

Straight-Through Ethernet Cables

Straight-through cable is the most common type and is used to connect different type of devices. This type of cable is easy to find in stores and can be used to:
1)Connect a computer to a switch/hub’s normal port.
2)Connect a computer to a cable/DSL modem’s LAN port.
3) Connect a router’s WAN port to a cable/DSL modem’s LAN port.
4) Connect a router’s LAN port to a switch/hub’s uplink port. (normally used for expanding network)
5) Connect 2 switches/hubs with one of the switch/hub using an uplink port and the other one using normal port.

If you need to check how straight-through cable looks like, it’s easy. Both side (side A and side B) of cable have wire arrangement with same color. For example, Cat5e UTP cable usually uses only four wires when sending and receiving information on the network. The four wires, which are used, are wires 1, 2, 3, and 6. When you configure the wire for the same pin at either end of the cable, this is known as a straight-through cable.

Crossover Ethernet Cables

Crossover cables are usually used to connect the same type of devices and may be a little harder to find since they aren’t used nearly as much as straight-through cables. A crossover cable can be used to:
1) Connect 2 computers directly.
2) Connect a router’s LAN port to a switch/hub’s normal port. (normally used for expanding network).
3) Connect 2 switches/hubs by using normal port in both switches/hubs.

Compared with straight-through Ethernet cables, the internal wiring of crossover cables reverses the transmit and receive signals. That is to say, the two end of the crossover Ethernet cable are wired differently. And the reversed color-coded wires can be seen through the RJ-45 connectors at each end of the cable.

Identifying Straight-Through and Crossover Cables

Whether they are straight-through or crossover cables, all Ethernet cables essentially look the same. When dealing with the inevitable pile of unlabeled cables that forms in every home, this can make dealing with them tricky. Fortunately, you can quickly identify crossover and straight cables if you know what to look for.

When determining if an Ethernet cable is a straight or crossover cable, examine the connectors. Observe the pin configuration carefully. The pins are color coded, so you should have no trouble doing this. If the pins are configured in the same way, you are looking at a straight cable. If not, it is a crossover cable.

Conclusion

Nowadays, the need for crossover cables has been eliminated with more modern equipment. Gigabit Ethernet was created with a widely used option called Auto-MDIX (automatic medium-dependent interface crossover). This technology detects whether you need a crossover cable or a straight-through cable, and it automatically configures the network interface card accordingly, which means that crossover function would be enabled automatically when it’s needed.