EPON — An Ideal Optical Access Network Solution

In recent years, the telecommunications backbone has experienced huge growth. The tremendous growth of Internet traffic has far surpassed the network capacity. The “last mile” still remains the bottle neck between high-capacity local area networks and the backbone network. So a new technology for optical access network, which is simple, scalable but not expensive, is needed. And that is Ethernet passive optical network (EPON).

EPON Definition

EPON, unlike other PON technologies which are based on the ATM standard, is based on the Ethernet standard. This lets you utilize the economies-of-scale of Ethernet, and provides simple, easy-to-manage connectivity to Ethernet-based, IP equipment, both at the customer premises and at the central office. As with other Gigabit Ethernet media, it is well-suited to carry packetized traffic, which is dominant at the access layer, as well as time-sensitive voice and video traffic.

EPON Network

An EPON network includes two parts: an optical line terminal (OLT) and an optical network unit (ONU).

The OLT resides in the central office (CO). This could typically be an Ethernet switch or Media Converter platform. OLT is mainly designed for controlling the information float across the optical distribution network (ODN). OLT has two float directions: upstream (getting an distributing different type of data and voice traffic from users) and downstream (getting data, voice and video traffic from metro network or from a long-haul network and sending it to all ONU modules on the ODN.

The ONU resides at or near the customer premise, in a building, or on the curb outside. It uses optical fiber for connecting to the PON on the one side, while interfacing with customers on the other side.

EPON Upstream and Downstream Traffic

In an EPON, the process of transmitting data downstream from the OLT to multiple ONU is fundamentally different from transmitting data upstream from multiple ONUs to the OLT.

In the downstream direction (from network to user), Ethernet frames transmitted by OLT pass through a 1:N (N represents the number of subscribers each fiber can serve) passive splitter and reach each ONU. Splitting ratios are usually between 4 and 64. At the splitter, the traffic is divided into separate signals, each carrying all of the ONU–specific packets. When the data reaches the ONU, it accepts the packets that are intended for it and discards the packets that are intended for other ONUs.

In the upstream direction (from user to network ), due to the directional properties of a passive combiner (optical splitter), data frames from any ONU will only reach the OLT, not other ONUs. Frames in EPON from different ONUs transmitted simultaneously may collide. Thus, ONUs need to share the trunk fiber channel capacity and resources.

EPON Advantages

First, EPON uses a point-to-multipoint topology instead of point--to-point in the outside plant. Thus it saves much of the cost of running fiber from every customer to the CO, installing active electronics at both ends of each fiber and managing all of the fiber connections at the CO. And EPON also eliminates active electronic components, such as regenerators and amplifiers, and replaces them with passive optical couplers that are less-expensive, simpler, and longer lived than active ones. As to the cost of expensive electronic components and lasers in the OLT, it will be shared over many subscribers not paid by each subscriber.

Second, EPON offers high bandwidth to subscriber. The traffic rates of 1Gbps in downstream and return traffic of 800 Mbps have been achieved already. Compared with point--to-point technology, EPON is specially made to address the unique demands of the access work. So more bandwidth can be got by each subscriber.

At last, the main advantage of EPON is that it can eliminate complex and expensive asynchronous transfer mode (ATM) and SONET elements and simplify the networks dramatically. Traditional telecom networks use a complex and multilayered architecture. While this architecture requires a router network to carry IP traffic, ATM switches to create virtual circuits, add/drop multiplexers (ADM) and digital cross-connects to manage SONET rings, and point-to-point DWDM optical links.

Summary

EPON is suitable for Fiber-to-the-Home/Building/Business applications, including voice, data and video services. EPON is a shared network but with much higher bandwidth. It’s a highly attractive access solution for service providers to extend fiber into the last mile because of low cost and good performance, resulting from their nature as passive networks, point-to-multipoint architecture, and native Ethernet protocol.

Originally published at www.fiber-optic-equipment.com

Which One Will You Choose for FTTx? PON or AON?

When it comes to FTTx deployment, there are two competing network solutions which are PON (Passive Optical Network) and AON (Active Optical Network). What is the difference between them? And which one will you choose? PON or AON? You may find the answer from the following contents.

PON

A PON consists of an optical line terminator (OLT) located at the Central Office (CO) and a set of associated optical network terminals (ONT) to terminate the fiber–usually located at the customer’s premise. Both devices require power. Instead of using powered electronics in the outside plant, PON uses passive splitters and couplers to divide up the bandwidth among the end users–typically 32 over a maximum distance of 10-20km.

AON

An active optical system uses electrically powered switching equipment to manage signal distribution and direct signals to specific customers. This switch opens and closes in various ways to direct the incoming and outgoing signals to the proper place. Thus, a subscriber can have a dedicated fiber running to his or her house. Active networks can serve a virtually unlimited number of subscribers over an 80km distance.

Advantages and Disadvantages of PON

• Advantages PON has some distinct advantages. It’s efficient, in that each fiber optic strand can serve up to 32 users. Compared to AON, PON has a lower building cost and lower maintenance costs. Because there are few moving or electrical parts and things don’t easily go wrong in a PON.
• Disadvantages PON also has some disadvantages. One of the biggest disadvantages is that these splitters have no intelligence, and therefore cannot be managed. Then you can’t check for problems cost-effectively when a service outage occurs. Another major disadvantage is its inflexibility. If one needs to re-design the network or pull a new strand of fiber from the upstream splitter, all downstream customers must come offline for changing the splitter in the network. At last, since PONs are shared networks, every subscriber gets the same bandwidth. So data transmission speed may slow down during peak usage times.

Advantages and Disadvantages of AON

• Advantages AON offers some advantages, as well. First, its reliance 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. Second, it’s about the distance. An active network has the distance limitation of 80 km regardless of the number of subscribers being served. At last, there are some other advantages like high flexibility for deploying different services to residential and business customers, and low subscriber cost.
• Disadvantages Like PON, AON also has its weaknesses. It needs at least one switch aggregator for every 48 subscribers. Because it requires power, AON inherently is less reliable than PON.

From the above contents, you can find that both technologies have its advantages and disadvantages. In some cases, FTTx systems actually combine elements of both passive and active architectures to form a hybrid system. Thus, to decide which technology to deploy, you should consider your own unique circumstances.

Originally published at www.china-cable-suppliers.com/

Why Does FTTH Develop So Rapidly?

FTTH (Fiber to the Home) is a form of fiber optic communication delivery in which the optical fiber reached the end users home or office space from the local exchange (service provider). FTTH was first introduced in 1999 and Japan was the first country to launch a major FTTH program. Now the deployment of FTTH is increasing rapidly. There are more than 100 million consumers use direct fiber optic connections worldwide. Why does FTTH develop so rapidly?

FTTH is a reliable and efficient technology which holds many advantages such as high bandwidth, low cost, fast speed and so on. This is why it is so popular with people and develops so rapidly. Now, let’s take a look at its advantages in the following.

• The most important benefit to FTTH is that it delivers high bandwidth and is a reliable and efficient technology. In a network, bandwidth is the ability to carry information. The more bandwidth, the more information can be carried in a given amount of time. Experts from FTTH Council say that FTTH is the only technology to meet consumers’ high bandwidth demands.
• Even though FTTH can provide the greatly enhanced bandwidth, the cost is not very high. According to the FTTH Council, cable companies spent $84 billion to pass almost 100 million households a decade ago with lower bandwidth and lower reliability. But it costs much less in today’s dollars to wire these households with FTTH technology.
• FTTH can provide faster connection speeds and larger carrying capacity than twisted pair conductors. For example, a single copper pair conductor can only carry six phone calls, while a single fiber pair can carry more than 2.5 million phone calls simultaneously. More and more companies from different business areas are installing it in thousands of locations all over the world.
• FTTH is also the only technology that can handle the futuristic internet uses when 3D “holographic” high-definition television and games (products already in use in industry, and on the drawing boards at big consumer electronics firms) will be in everyday use in households around the world. Think 20 to 30 Gigabits per second in a decade. No current technologies can reach this purpose.
• The FTTH broadband connection will bring about the creation of new products as they open new possibilities for data transmission rate. Just as some items that now may seem very common were not even on the drawing board 5 or 10 years ago, such as mobile video, iPods, HDTV, telemedicine, remote pet monitoring and thousands of other products. FTTH broadband connections will inspire new products and services and could open entire new sectors in the business world, experts at the FTTH Council say.
• FTTH broadband connections will also allow consumers to “bundle” their communications services. For example, a consumer could receive telephone, video, audio, television and just about any other kind of digital data stream using a simple FTTH broadband connection. This arrangement would more cost-effective and simpler than receiving those services via different lines.

As the demand for broadband capacity continues to grow, it’s likely governments and private developers will do more to bring FTTH broadband connections to more homes. According to a report, Asian countries tend to outpace the rest of the world in FTTH market penetration. Because governments of Asia Pacific countries have made FTTH broadband connections an important strategic consideration in building their infrastructure. South Korea, one of Asian countries, is a world leader with more than 31 percent of its households boasting FTTH broadband connections. Other countries like Japan, the United States, and some western countries are also building their FTTH broadband connections network largely. It’s an inevitable trend that FTTH will continue to grow worldwide.

Originally published at www.china-cable-suppliers.com

Fiber Optic Connector Cleaning

With the deployment of 40G and 100G systems in the data center, reliable and efficient fiber installations are critical to the high performance network. Contaminated fiber optic connectors can often lead to degraded performance. Any contamination on the fiber connectors can cause failure of the component or failure of the whole system. So it’s important to keep fiber connectors clean.

Contamination Sources

There are two most important forms of contamination on fiber connectors and they are oils and dust. Oils from human hands will leave a noticeable defect easily seen with a fiberscope. The oil will trap dust against the fiber and bring scratches to the fiber connector. Inserting and removing a fiber can create a small static charge on the ends, which can attract airborne dust particles. Simply removing and re-inserting a fiber may also contaminate the end of the connector with a higher level of dust. Fiber caps, which are used to prevent fiber ends from being contaminated while not seated in a connector, will collect dust, dirt, oil and other contaminants to the fiber when used. Except oil and dust, there also other types of contamination, such as film residues condensed from vapors in the air, powdery coatings leaving after water or other solvents evaporating away. These contaminates tend to more difficult to remove and can also cause damage to equipment if not removed.

Contamination Inspection Tools

To inspect whether a fiber connector is contaminated, one should use fiberscope, clean and resealable container for the endcaps, bulkhead probe. A fiberscope is a customized microscope for inspecting optical fiber components. The fiberscope should provide at least 200x total magnification. The bulkhead probe is a handheld fiberscope used in order to inspect connectors in a bulkhead, backplane, or receptacle port. It should provide at least 200x total magnification displayed on a video monitor.

Contamination Inspection Steps

With contamination inspection tools, you should know how to inspect fiber connectors. The following introduces the inspection steps:

• Make sure that the lasers are turned off before you begin the inspection. Be careful: Invisible laser radiation might be emitted from disconnected fibers or connectors. Do not stare into beams or view directly with optical instruments.
• Remove the protective cap and store it in a clean resealable container. Verify the style of connector you inspect and put the appropriate inspection adapter or probe on your equipment.
• Insert the fiber connector into the fiberscope adapter, and adjust the focus ring so that you see a clear endface image. Or, place the tip of the handheld probe into the bulkhead connector and adjust the focus.
• On the video monitor, see if there is contamination present on the connector endface (See the following figure).

Connector Cleaning Tools

If there is contamination inspected on the fiber connector, then you need to clean it with proper tools. These tools can be divided into four types based on the cleaning method.

• Dry cleaning: Optic cleaning without the use of any solvent like such as one click fiber optic cleaner for 2.5mm connector (See the following figure).

• Wet cleaning: Optic cleaning with a solvent.
• Non-Abrasive cleaning: Cleaning without abrasive material touching the fiber optic connector end face.
• Abrasive cleaning: The popular lint free wipes, such as fiber optic mini foam swabs.

Connector Cleaning Steps

How to clean the fiber connector? Here is about the cleaning steps with abrasive cleaning tools.

• Gently wipe endface with lint-free pad in one direction.
• Using a can with compressed gas held upright and approximately 2 inches from the connector end, release a stream of gas on the connector endface for no more than 5 seconds.
• Gently wipe the ferrule and the end-face surface of the connector with an alcohol pad. Making sure the pad makes full contact with the end-face surface. Wait 5 seconds for the surface to dry.

After finishing the cleaning steps, you should better inspect again to make sure there is definitely no contamination on the connector. Remember never touch the end face of the fiber connector and always install dust caps on unplugged fiber connectors. Do not re-use optic cleaning swabs or lens paper (lint free wipes).

Originally published at www.china-cable-suppliers.com/

Understanding of Optical Losses for Better Data Transmission

When light propagates as a guided wave in a fiber core, it experiences some power losses. These are particularly important for signal transmission through fiber optic cables over long distance. For better telecommunication, we should try to decrease optical losses. Then first we need to know well about optical losses. The article will tell about intrinsic fiber losses and extrinsic fiber losses.

Intrinsic Fiber Losses

Intrinsic fiber losses are those associated with the fiber optic material itself. There are two kinds: scattering losses and absorption losses (see the following picture). Light is attenuated mainly because of these.

• Absorption Losses Absorption loss is caused by absorption of photons within the fiber such as metal ions (e.g., Cu2+, Fe3+) and hydroxyl (OH–) ions. Optical power is absorbed in the excitation of molecular vibrations of such impurities in the glass. One absorption feature is that it occurs only in the vicinity of definite wavelengths corresponding to the natural oscillation frequencies or their harmonics of the particular material. In modern fibers, absorption losses are almost entirely cuased by OH–1 ions. The fundamental vibration mode of these ions corresponds to l = 2.73 µm and the harmonics at 1.37 and 0.95 µm. To reduce presence of OH1 ions, it’s possible to employ dehydration.
• Scattering Losses Scattering losses are the second dominat influence factor to the signal attenucation in an optical fiber. This kind of loss is caused by micro variations in the fiber material density, which occur during the manufacturing process. Even though the careful manufacturing techniques is advanced and careful, most fibers are still inhomogeneous with disordered and amorphous structures. The scattering losses decrease in porption to the fourth power of the signal wavelength. So the scattering loss is a dominant loss mechanism below wavelengths of 1,000 nm. It’s also necessary in the third transmission window at the wavelengths of 1,550 nm.

Extrinsic Fiber Losses

These losses are specific to geometry and handling of the fibers and are not functions of the fiber material itself. There are two basic kinds and they are bending losses and connector losses.

• Bending Losses When optical fiber cables are bent, they exhibit additional propagation losses. This is called bending losses which is a frequently encountered problem in fiber optics. Typically, these losses rise very quickly once a certain critical bend radius is reached. This critical radius can be very small (a few millimeters) for fibers with robust guiding characteristics (high numerical aperture), or it can be much larger (often tens of centimeters) for single-mode fibers. Losses are greater for bends with smaller radius.
• Connector Losses Connector losses are related to the coupling of the output of one fiber with the input of another fiber, or couplings with detectors or other components. The losses may arise in fiber connectors and splices of the joined fibers with cores of different diameters or misaligned centers. Or the losses may occur if fibers’ axes are titled. The losses caused by mismatching of fiber diameters can be approximated by –10 log(d/D). There are other connection losses such as offsets or air gaps between fibers, and poor surface finishes.

From this article, you may know something about optical losses. To get better data transmission, you should consider the above influence factors. For intrinsic fiber losses, the products’ material is critical. For extrinsic fiber losses, note that you should try to avoid bending the fiber and do good coupling of fibers, joining fibers with the same diameters, avoid the fiber axes titled, etc.

Originally published at www.china-cable-suppliers.com/

Fiber Optic Splicing

Fiber optic splicing is one of the fiber optic terminations which creates a permanent joint between the two fibers. With the benefits of low light loss and back reflection, fiber optic splicing is a preferred method when the cable runs are too long for a single length of fiber or then joining two different types of cables together. There are two methods of splicing, fusion splicing and mechanical splicing.

Fusion Splicing

In fusion splicing (as following picture), a machine called fusion splicer is used to precisely align the two fiber ends. Then the glass ends are "fused" or "welded" together using some type of heat or electric arc. This produces a permanent connection between the fibers enabling very low loss light transmission (Typical loss: 0.1 dB). Fusion splicing has the best return loss performance of all the mating and splicing techniques.

Fusion Splicing Steps

• Prepare the fiber. Strip the protective coatings, jackets, tubes, strength members, etc. and only leave the bare fiber showing. Please pay attention to keep the fiber clean.
• Cleave the fiber. Choose a good fiber cleaver. The cleaved end must be mirror-smooth and perpendicular to the fiber axis to obtain a proper splice. But the cleaver is not used to cut the fiber. It’s only used to produce a cleaved end that is as perpendicular as possible.
• Fuse the fiber. Align the fusion splicer unit and use an electrical arc to melt the fibers, permanently welding the two fiber ends together. Alignment can be manual or automatic.
• Protect the fiber - To ensure the splice not break during normal handling, you must protect the fiber from bending and tensile forces. A typical fusion splice has a tensile strength between 0.5 and 1.5 lbs and will not break during normal handling but it still requires protection from excessive bending and pulling forces.

Mechanical Splicing

Mechanical splicing (as following picture) aligns and mates the end face of two cleaned and cleaved fiber tip together. It’s a reusable splice. The mechanical splice will have an index matching fluid that eliminates the fiber-to-air interface, there by resulting in less back reflections. Mechanical splices are often used when splices need to be made quickly and easily.

Mechanical Splicing Steps

• Prepare the fiber. Strip the protective coatings, jackets, tubes, strength members, etc. and only leave the bare fiber showing. Please pay attention to keep the fiber clean.
• Cleave the fiber. This one is the same to the fusion splicing step. But the cleave precision is as critical.
• Mechanically join the fibers. This method doesn’t use heat. Simply put the fiber ends together inside the mechanical splice unit. The index matching fluid inside the mechanical splice apparatus will help couple the light from one fiber end to the other. Older apparatus will have an epoxy rather than the index matching fluid holding the cores together.
• Protect the fiber - the completed mechanical splice provides its own protection for the splice.

Which One Should You Choose?

To decide which fiber splicing method you should choose, you may take two important factors into consideration. First, it’s the cost. Mechanical splicing has a low initial investment ($1,000—$2,000) but costs more per splice ($12-$40 each). While the initial investment is about at least $15,000 and per splice cost is about $0.50 - $1.50. Second, it’s the performance. Fusion splicing offers a high degree performance of lower loss and less back reflection than mechanical splicing.

By the comparison of the cost and performance of two methods, now you know which one is suitable for your applications. If you have enough money and need more precise alignment for lower loss, you could buy a fusion splicing machine. If you just have a small budget and should make a quick splice, then you can choose mechanical fiber optic splice.

Originally published at www.china-cable-suppliers.com/

Passive Optical Network Technology

The tremendous growth in IP traffic badly influenced the access network capacity. It’s believed that the copper-based access networks can’t provide either the minimum bandwidth or the required transmission distance for delivering services of voice, data, and video programs. Passive optical network (PON) is seemed as a promising and cost-effective way to solve this problem.

What’s PON?

PON is a telecommunication network that uses point-to-multipoint fiber to the end-points in which optical splitters are used to enable a single optical fiber to serve multiple end-points. It does not include any electrically powered switching equipment.

Three Devices in PON

There are three distinct devices in the network (as shown in the following picture): the OLT (optical line terminal), the ONUs (optical network units) or ONTs (optical network terminals) and the splitter. Each one has a necessary function in the passive optical network. PON always works under transmission between the OLT and the different ONT’s through optical splitters, which multiplex or demultiplex signals based on their origin and destination.

• OLTs are located in provider’s central switching office. This equipment serves as the point of origination for FTTP (Fiber-to-the-Premises) transmissions coming into and out of the national provider’s network. An OLT, is where the PON cards reside.
• ONU converts optical signals transmitted via fiber to electrical signals. These electrical signals are then sent to individual subscribers. ONUs are commonly used in fiber-to-the-home (FTTH) or fiber-to-the-curb (FTTC) applications. Using different wavelengths for each service makes it possible to transmit high-speed Internet and video services at the same time. Wavelength multiplexing is performed at the central office and a wavelength demultiplexing mechanism is provided at the customer's house.
• PON splitter is used to split the fiber optic light into several parts at a certain ratio. For example, a 1X2 50:50 fiber optic splitter will split a fiber optic light beam into two parts, each get 50 percent of the original beam.

Advantages of PON

There are many advantages given by the use of fiber and the passive elements that compose the network. The following will tell about the advantages of PON.

• High bandwidth The bandwidth allowed by systems based on PON can reach the 10 Gbps rate down to the user. The need to increase the bandwidth and the speed is another justification for the use of PON.
• Long distance A PON allows for longer distances between central offices and customer premises. While with the Digital Subscriber Line (DSL) the maximum distance between the central office and the customer is only 18000 feet (approximately 5.5 km), a PON local loop can operate at distances of over 20 km.
• Low cost On one hand, the cost of passive elements is low. On the other hand, the installation of these PON elements is much more economic. And it avoids operation and maintenance costs, such as absence of falls or maintenance of the network feeds.

Of course PON has some disadvantages. Compared with an active optical network, it has less range. That means subscribers must be geographically closer to the central source of the data. PON also make it difficult to isolate a failure when they occur. However, these disadvantages can not avoid choosing PON as the best possible configuration. Because it saves the cost of deploying PON networks regarding other two configurations (point to point and active optical network). And the flexibility of the network allows the usage of a channel by a large number of users.

Originally published at www.china-cable-suppliers.com/