Difference Between AON and PON

AON (Active Optical Networks) and PON (Passive Optical Network) serve as the two main methods of building CWDM and DWDM backbone network. Each of them has their own merits and demerits. This article will compare them according to their different features and applications.

AON

An active optical system uses electrically powered switching equipment, such as a router or a switch aggregator, to manage signal distribution and direction signals to specific customers. This switch directs the incoming and outgoing signals to the proper place by opening and closing in various ways. In such a system, a customer may have a dedicated fiber running to his or her house. The reliance of AON on Ethernet technology makes interoperability among vendors easy. Subscribers can select hardware that delivers an appropriate data transmission rate and scale up as their needs increase without having to restructure the network. However, AON require at least one switch aggregator for every 48 subscribes. Since it requires power, an active optical network inherently is less reliable than a passive optical network.

PON

A PON is made up of an optical line termination (OLT) at the service provider’s central office and a number of optical network units (ONUs) near end users. Typically, up to 32 ONUs can be connected to an OLT. The passive optical network simply describes the fact that optical transmission has no power requirements or active electronic parts once the signal is going through the network.

A PON system makes it possible to share expensive components for FTTH. A PON splitter takes one input and splits it to broadcast to many users, which can lower the cost of the links substantially by sharing, for example, one expensive laser with up to 32 homes. PON splitters are bi-directional, that is signals can be sent downstream from the central office, broadcast to all users, and signals from the users can be sent upstream and combined into one fiber to communicate with the central office.

A passive optical network does not include electrically powered switching equipment. It uses optical splitters to separate and collect optical signals as they move through the network. A PON shares fiber optic strands for portions of the network. Powered equipment is required only at the source and receiving ends of the signal. PONs are efficient since each fiber optic strand can serve up to 32 users. Besides, PONs have a low building cost compared with active optical networks along with lower maintenance cost. However, PONs also have some demerits. They have less range than an AON, which means subscribes must be geographically closer to the central source of the data. When a failure occurs, it is rather difficult to isolate it in a PONs. Moreover, because the bandwidth in a PON is not dedicated to individual subscribers, data transmission speed may slow down during peak usage times in an effect known as latency. And latency would quickly degrade services such as audio and video, which need a smooth rate to maintain quality.

AON vs. PON

As early as the year 2009, PONs began appearing in corporate networks. Users were adopting these networks because they were cheaper, faster, lower in power consumption, easier to provision for voice, data and video, and easier to manage, since they were originally designed to connect millions of homes for telephone, Internet and TV services.

Passive Optical Networks (PON) provide high-speed, high-bandwidth and secure voice, video and data service delivery over a combined fiber network. The main benefits of PON are listed below:

• Lower network operational costs
• Elimination of Ethernet switches in the network
• Elimination of recurring costs associated with a fabric of Ethernet switches in the network
• Lower installation (CapEx) costs for a new or upgraded network (min 200 users)
• Lower network energy (OpEx) costs
• Less network infrastructure
• You can reclaim wiring closet (IDF) real estate
• Large bundles of copper cable are replaced with small single mode optical fiber cable
• PON provides increased distance between data center and desktop (>20 kilometers)
• Network maintenance is easier and less expensive
• Fiber is more secured than copper. It is harder to tap. There is no available sniffer port on a passive optical splitter. Data is encrypted between the OLT and the ONT.

Conclusion

To sum up, the PON network’s predefined topology makes individual changes more difficult. By terminating all the fiber optics at the OLT, i.e. the same fiber optic topology as in the AON (point-to-point), this disadvantage can be overcome. Therefore, for future-proof infrastructure investment, reliable point-to-point fiber optics technology should always be considered.

CWDM and DWDM Network Solutions

Growing demands of the internet users is one of the reasons that lead using wavelength division multiplexing (WDM) networks to transmit optical data. So, what is WDM? WDM is a technology that multiplexes various optical signals through a single optical fiber by taking advantage of different wavelengths of laser light. And the ITU-T recommendation specifies the wavelengths used in CWDM/DWDM or OADM. All the passive fiber optic components are made of filters that only allow specific wavelength to pass through a fiber port and then the others to be reflected to another fiber ports.

WDM Network Overview

A WDM network uses a multiplexer at the transmitter to join the several signals together, and a demultiplexer at the receiver to split them apart. With the increasing demand of data, video and mobile usage on many networks, WDM technology has proved to be the most reliable and cost-effective in transporting large amount of data in telecom. And by utilizing CWDM and DWDM network systems to scale the bandwidth, the operators enable to transmit service from 2Mbps up to 100Gbps of data. Now WDMs are very popular in field of CATV, Internet, VoIP, audio and video solutions, and even bring FTTX solutions to the people’s daily life.

CWDM Network Solutions

CWDM stands for Course Wavelength Division Multiplexer. “Course” means the channel spacing is 20nm with a working channel pass band (±6.5nm or ±7.5nm) from the wavelengths center. CWDM MUX DEMUX Modules take advantage of conventional thin-film filter (TFFS) technology and that allow various channels within ITU G.694 Grid (1270nm~1610nm,1271nm~1611nm), to realize multiplexing or demultiplexing wavelengths over one fiber. Due to the use of cheaper CWDM uncooled laser or lower-quality multiplexer and demultiplexers without fiber amplifiers. The CWDM works at a 60 or 80 km transmission with the wavelength of 1550nm. So CWDM is a very attractive options in metro networks.

DWDM Network Solutions

DWDM stands for Dense Wavelength Division Multiplexer. The word “Dense” is referring to the very narrow channel spacing measured in Gigahertz (GHz) as opposed to nanometer (nm). DWDM us typically use channel spacing measured in GHz (100G or 200G, C-Band 1525nm~1565nm). Now an optical fiber inter-leaver or optic fiber chip is used to double the channel of 100GHz or 200GHz spacing, that’s 50GHz or 100GHz AWG. Just like CWDM MUX DEMUX, DWDM MUX DEMUX also takes the advantage of thin-film filters and are used to increase the amount of data capacity that can be transmitted over a single fiber. The DWDM will be with more channels with much tighter channel spacing. Typical DWDM MUX DEMUX modules only have 32, 40, 44 channels but today’s 50Ghz 100Ghz DWDM MUX DEMUX doubles the channel spacing and can reach up to 64, 80, 88 and even 90 channels.

DWDM is the most suitable technology for long-haul transmission because of its ability to allow EDFA amplification. Given the growing need for bandwidth driven by data-hungry applications (smartphones, video streaming, etc.), DWDM has now found its way into metro networks, and is even being used in some cellular back-haul deployments.

Conclusion

WDM systems have become one of the major solutions to meet the growing demand for increased network bandwidth brought about by the rapid growth of Internet and data services. CWDM and DWDM network solutions have their own suitable applications. If you want to get more details for these solutions, kindly visit www.fs.com.

CWDM vs. DWDM

WDM (Wavelength Division Multiplexing) is a method of transmitting data from different sources on a single fiber whereby each data channel is carried on its own unique wavelength. A WDM system uses a CWDM or DWDM multiplexer at the transmitter to join various signals together, and a demultiplexer at the receiver to split them apart. Coarse Wavelength Division Multiplexing (CWDM) and Dense Wavelength Division Multiplexing (DWDM) are both mature WDM technologies, using standardized ITU-T wavelengths. This article will make a comparison between them according to their corresponding characteristics and applications.

CWDM is currently well-positioned to help carriers maximize their network capacity in the access, metro and regional network segments. CWDM supports fewer wavelengths than DWDM, but is available at a fraction of the cost of DWDM. This makes CWDM attractive for areas with moderate traffic growth projections. Thus CWDM is the ideal choice for cost efficiently short-haul transmission in telecoms or enterprise networks. While DWDM is designed for long-haul transmission where wavelengths are packed tightly together, providing a high-capacity solution in telecom networks. Generally speaking, DWDM and CWDM are based on the same concept of using multiple wavelengths of light on a single fiber, but differ in the wavelengths spacing, number of channels and the ability to amplify the multiplexed signals in the optical space.

The major difference between them is that DWDM multiplexing systems are made for longer haul transmission, by keeping the wavelengths tightly packed. They can transmit more data over a significantly larger run of cable with less interference than a comparable CWDM system. CWDM cannot travel long distances because the wavelengths are not amplified, and therefore CWDM is limited in its functionality over longer distances. Therefore, DWDM technology is one of the best choices for transporting extremely large amounts of data traffic over long distance in optical networks.

Compared with DWDM which is a more tightly packed WDM system, CWDM has larger wavelengths spacing with fewer wavelengths be transported on the same fiber. For instance, CWDM typically has 20 nm wavelengths spacing while DWDM typically has approximately 0.8 nm, hence can pack 40 plus channels compared to CWDM in the same frequency range. Thus, more channels and higher capacity can be achieved using DWDM.

CWDM systems, on the other hand, use DFB lasers that are not cooled. These systems typically operate from 0 to 70°C with the laser wavelength drifting about 6 nm over this range. This wavelength drift, coupled with the variation in laser wavelength of up to ±3 nm (due to laser die manufacturing processes), yields a total wavelength variation of about ±12 nm. However, DWDM systems require larger cooled DFB lasers for a semiconductor laser wavelength drifts about 0.08 nm/°C with temperature. The use of uncooled lasers causes lower energy consumption, which has positive financial implications for systems operators. For instance, the cost of the battery is minimized with the decreasing of energy consumption, which reduces operating costs. So DWDM systems are more expensive than CWDM systems for the application of cooled lasers.

In conclusion, CWDM and DWDM differ in complexity, offered capacity, cost and the markets they address. Due to its low cost and simple deployment, CWDM is a good fit for access networks and many metro/regional networks. While DWDM increases the distances between network elements, which is a huge benefit for long-haul service providers looking to reduce their initial network investment significantly.

Necessary Components in DWDM Systems

DWDM (Dense Wavelength Division Multiplexing) is used to increase the amount of information or systems that can be transmitted over a single fiber, thus allowing allow for more channels with much tighter channel spacing. In DWDM systems, DWDM devices combine the output from several optical transmitters for transmission across a single optical fiber. At the receiving end, another DWDM device separates the combined optical signals and passes each channel to an optical receiver. This article covers DWDM system components that combine (multiplex) and separate (demultiplex) multiple optical signals of different wavelengths in a single fiber.

Optical Transmitters/Receivers

As the light sources in a DWDM system, the optical transmitters are of great importance to the whole system design. In DWDM systems, multiple transmitters are used to provide the source signals which are then multiplexed. Incoming electrical data bits (0 or 1) trigger the modulation of a light stream (e.g., a flash of light = 1, the absence of light = 0). Lasers create pulses of light, each with an exact wavelength. In an optical-carrier-based system, a stream of digital information is delivered to a physical layer device, whose output is a light source (an LED or a laser) that interfaces a fiber optic cable. Then the device converts the incoming electrical signals to optical form signals. Electrical ones and zeroes trigger a light source that flashes light into the core of an optical fiber. The format of the underlying digital signal is not changed. Pulses of light propagate across the optical fiber by total internal reflection. At the receiving end, another optical sensor (photodiode) detects light pulses and converts the incoming optical signals back to electrical signals. Two fibers are used in this process, one for transmitting and the other for receiving.

DWDM Mux/DeMux Modules

The DWDM Mux combines multiple wavelengths created by multiple transmitters and operating on different fibers. The output signal of an multiplexer is referred to as a composite signal. At the receiving end, the DEMUX (demultiplexer) separates all of the individual wavelengths of the composite signal out to individual fibers. The individual fibers pass the demultiplexed wavelengths to as many optical receivers. Generally, MUX and DEMUX components are contained in a single enclosure. Optical MUX DEMUX devices can be passive. Component signals are multiplexed and demultiplexed optically, not electronically, therefore no external power source is required.

Optical Add/Drop Multiplexers (OADM)

In a DWDM system, the optical add/drop multiplexers (OADM) can add or drop DWDM channels into an existing backbone ring. It provides the ability to drop one DWDM 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.

Optical Fiber Amplifiers

Optical fiber amplifiers boost the amplitude or add gain to optical signals passing on a fiber by directly stimulating the photons of the signal with extra energy. Optical fiber amplifiers amplify optical signals across a broad range of wavelengths. They can provide flat gain over a large dynamic gain range, have a high saturated output power, low noise, and effective transient suppression. Erbium-doped fiber amplifier (EDFA) is the most widely used fiber amplifier which has received great attention over the past 10 years. EDFA amplifier is generally used for very long fiber links such as undersea cabling. It uses a fiber that has been treated or "doped" with erbium, and this is used as the amplification medium.

Transponders (OEO)

Transponders are also referred to as optical-electrical-optical (O-E-O) wavelength converters. They can convert optical signals from one incoming wavelength to another outgoing wavelength suitable for DWDM applications. A transponder performs an O-E-O operation to convert wavelengths of light. Within the DWDM system, a transponder converts the client optical signal back to an electrical signal (O-E) and then performs either 2R (reamplify, reshape) or 3R (reamplify, reshape and retime) functions.

Conclusion

With all the necessary components, DWDM-based networks can transmit data in IP, ATM, SONET, SDH and Ethernet. Therefore, DWDM-based networks can carry different types of traffic at different speeds over an optical channel. If you want to learn more about all these components for DWDM system, kindly visit www.fs.com for more details.

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.