What Should You Know Before Using an OTDR?

OTDR, the optical time domain reflectometer, is the most important investigation tool for optical fibers. It’s applied in the measurement of fiber loss, connector loss and for the determination of the exact place and the value of cable discontinuities. It’s the only device which can verify inline splices on concatenated fiber optic cables and locating faults.

To know how to use OTDR for the fiber investigations, first you should know the structure and working principle of OTDR equipment. When a short light pulse transmits into the fiber under test, the time of the incidence and the amplitude of the reflected pulses are measured. The commonly used pulse width ranges from nanosecs to microsecs, the power of the pulse can exceed 10 mW. The repetition frequency depends on the fiber length, typically is between 1 and 20 kHz, naturally it is smaller for longer fibers. The division by 2 at the inputs of oscilloscope is needed since both the vertical (loss) and the horizontal (length) scales correspond to the one-way length.

Besides, to use an OTDR successfully, you should also know how to operate the instrument. The following is about the experiences collected from some experienced people who use OTDRs during installation and for maintaining telecommunication networks.

Keep Connectors Clean

Before use OTDR, first, you should watch out if the connectors are clean. If it’s dirty, then clean it. Otherwise, it will make measurements unreliable, noisy or even impossible. What’s worse, it may damage the OTDR.

Check the Connector or the Patch Cord

Check whether the patch cord, the module, and the fiber under test are single-mode or multimode. To test the patch cord, activate the laser in the CW (Coarse Wavelength) mode and measure the power at the end of the patch cord with a power meter. This should be between 0 and - 4 dBm for most single-mode modules and wavelengths.

Set the Range

The range is the distance over the cable which the OTDR will measure. The range should be longer than the cable you are testing. For example, if your link is 56.3 km long, choose 60 km. For distances greater than approximately 15 km, make your first measurement in longhaul mode, otherwise use shorthaul.

Determine the Wavelength

Usually single-mode is set for 1310 nm or 1550 nm, and multimode is set for 850 nm or 1300 nm.

Averages of Noisy Traces

If the trace is very noisy, increase the number of averages. Usually 16-64 averages are adequate. To improve the signal to noise ration of the trace, the OTDR can average multiple measurements, but averaging takes time. So try to average over a longer time.

Realtime Mode

In this mode, you can modify parameters only if you stop a measurement explicitly. So it avoids you to erase a trace averaged over a long time by accident. You use realtime mode to check your connection, the quality of splices, and whether a fiber is connected. Start in automatic mode, then switch to realtime mode and select the most suitable parameters.

Adjust the Refractive Index

If you know the exact physical length of the fiber under test, you can measure the refractive index. Start with the refractive index 1.5000. Place a marker at the end of the fiber. Then select the refractive index function and adjust it until the displayed marker position is equal to the known fiber length. Then, the effective refractive index will be displayed.

Macrobending Loss

Single-mode fibers (1550 nm) are very sensitive to macrobending such as a tight bend or local pressure on the cable. It doesn’t always happen at this wavelength of 1310 nm. So characterize your link at both wavelengths.

OTDRs are invaluable test instruments. Maybe a small mistake will cause serious damage to this equipment. So before use it, you should better know it as detailed as possible to avoid any loss because of innocence and make full use of it in optical fiber events.

Originally published at http://www.articlesxpert.com/article/1182251/what-should-you-know-before-using-an-otdr/

How to Choose a Right OTDR?

An optical time-domain reflectometer (OTDR) is an optoelectronic instrument used to measure fiber loss, the loss and reflectance of fiber splices, and to locate loss irregularities within the fiber. Now there are many types of OTDRs providing different test and measurement needs including very simple fault finders and advanced OTDRs for link certification. Then, how to choose the right one?

First, you should evaluate your needs. Installing or maintaining fiber? For simple maintenance, a simple or low cost OTDR is good. It’s easy to use, requires the lowest possible investment and some even provides total link loss and optical return loss values. For not very complex installation, you should choose a mini OTDR based on the following key parameters for your specific environment.

Dynamic Range

This specification determines the total optical loss that the OTDR can analyze; i.e., the overall length of a fiber link that can be measured by the unit. The higher the dynamic range, the longer the distance the OTDR can analyze. Insufficient dynamic range will influence the ability to measure the complete link length and affect the accuracy of the link loss, attenuation and far-end connector losses. It’s good to choose an OTDR whose dynamic range is 5 to 8 dB higher than the maximum loss you will encounter.

Dead Zones

Dead zones originate from reflective events (connectors, mechanical splices, etc.) along the link, and they affect the OTDR’s ability to accurately measure attenuation on shorter links and differentiate closely spaced events, such as connectors in patch panels, etc. There are two types of dead zones to specify OTDR performance:

Attenuation dead zone refers to the minimum distance required, after a reflective event, for the OTDR to measure a reflective or non-reflective event loss. Try to choose OTDR with the shortest possible attenuation dead zone to measure short links and to characterize or find faults in patchcords and leads. Industry standard values range from 3 m to 10 m for this specification.

Event dead zone is the distance after a reflective event starts until another reflection can be detected. If a reflective event is within the event dead zone of the preceding event. Industry standard values range from 1 m to 5 m for this specification. The event dead zone specification is always smaller than the attenuation dead zone specification.

Sampling Resolution

Sampling resolution refers to the minimum distance between two consecutive sampling points acquired by the instrument. This is a quite important parameter as it defines the ultimate distance accuracy and fault-finding capability of the OTDR.

Pass/Fail Thresholds

This parameter is also important because lots of time can be saved in the analysis of OTDR traces if you set Pass/Fail thresholds for parameters of interest (e.g., such as splice loss or connector reflection). These thresholds highlight parameters that have exceeded a Warning or Fail limit set and, when used in conjunction with reporting software, it can rapidly provide re-work sheets for installation/commissioning engineers.

Report Generation

If an OTDR has specialized post-processing software allowing fast and easy generation of OTDR reports, it can save up to 90% post-processing time. These can also include bidirectional analyses of OTDR traces and summary reports for high-fiber-count cables.

To choose a right OTDR for your test application, you should better consider the above factors. Fiberstore offers JDSU MTS-4000, YOKOGAWA AQ1200 MFT-OTDR, EXFO AXS-110-023B OTDR 1310/1550 nm (37/35 dB), etc,. with great accuracy, measurement range and instrument resolution. There must be one suitable for you and helpful to maximize your return on investment.

Originally published at http://www.articlesfactory.com/articles/communication/how-to-choose-a-right-otdr.html

Which One Will You Choose? Cat 5e, Cat 6 or Cat 6a?

Copper is the oldest installed cable and it’s still widely used for connecting devices. Till now, copper cable has gone through several generations to meet people’s increasing needs of different sides. There are many types of copper cables offering different performance such as Cat 5e, Cat 6 or Cat 6a. What kind of copper cabling should you choose? This is a really confusing question people usually meet today. This article will introduce some details about these three kinds of copper cables and help you make your decision.

Cat 5e

Cat 5e, also known as Enhanced Category 5, is designed to support full-duplex Fast Ethernet operation and Gigabit Ethernet. In 1998, Gigabit Ethernet was introduced. Then, the original Cat 5 was found not good enough to guarantee error-free performance. So extra requirements were added to Cat 5, such as Return Loss, Delay, Delay Skew and Power Sum Crosstalk measurements. With these improved parameters, Cat 5e came into being to ensure reliable operation of Gigabit Ethernet. The electrical performance for Cat 5e requirements is up to 100MHz.

Cat 6

Cat 6 was designed as the next generation to Cat 5e. It has higher standards construction than Cat 5e with a bandwidth of up to 250 MHz rather than 100 MHz. It can support the faster protocols and is therefore considered more reliable than Cat 5e. It is ideal for 10 Gigabit Ethernet transmissions.

Cat 6a

Cat 6a has a bandwidth of up to 500 MHz and is designed to support 10 Gigabit Ethernet transmissions over 100 meter channel. It’s also compatible with Cat 5e and Cat 6. A new electrical parameter measure of “alien crosstalk”, which is a measurement of the noise crosstalk generated from neighboring cables, was introduced to ensure that Cat 6a cabling system can run 10 Gigabit Ethernet transmissions well.

Common Features of Three Types

The three kinds of cables are unshielded twisted pair (UTP) or shielded twisted cables. They use 4 twisted pairs in a common jacket and the same RJ-45 jacks and plugs. And they are limited to a cable length of 100 meters including the length of the patch cables on either end of the link. The parts are interchangeable. That means you can use a Cat 5e patch cable with Cat 6 house cabling. But your system will perform at the lowest link level.

Differences of Three Types

The most noticeable difference of these cables is the price. According to statistics, plan on Cat 6 will cost roughly 30% more than Cat 5e and Cat 6a 30% more than Cat6. But the price is not the only factors to decide which kind of cable should be used.

• Transmission Performance: Cat 5e has a bandwidth of up to 100 MHz. It has a reduced maximum length of 45 meters when used for 10 Gigabit Ethernet applications. Cat 6 cable is rated for 250 MHz. It can support 10 Gigabit Ethernet up to 55 meters. While Cat 6a performs at up to 500 MHz, so it allows 10 Gigabit Ethernet to be run over distances of up to 100 meters. Cat 6a has a better transmission performance than Cat 6 and Cat 5e. But this doesn’t mean the network ‘speed’ of Cat 6a is faster. These are electrical performance differences.
• Crosstalk: Crosstalk is a complicated subject to grasp and has been talked before. It is the phenomenon in which a signal from one channel or circuit interferes with another channel or circuit's signal. Cat 6 cable has lower signal degradation from near-end crosstalk (NEXT), power sum NEXT (PS-NEXT) and attenuation than Cat 5e. Cat 6a reduces this to an even lower level.
• Physical Properties: Cat 6a has bigger size and more weights than Cat 5e and Cat 6. It will take up more space for installation. And because of the larger cable diameter, Cat 6a needs a bigger bend radius. So it’s important to allow extra space anywhere for Cat 6a cables. Since it's capable of speeds up to 500 MHz and Alien Crosstalk begins at only 350 MHz, Cat 6a needs more testing.

Which One Should You Choose?

For most of copper network applications, Cat 5e is good enough to give all the performance we are likely to need today. But if you are looking for a cable for your future needs, then Cat 6a will give you the best performance at full distances. So it depends on what you will do with the cable. You should also consider the price and space.

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

EPON vs. GPON—Which Will Be More Popular?

With the development of passive optical networking (PON) technology, two PON standards are striking in FTTH solution area and they are Ethernet passive optical networking (EPON) and ATM (asynchronous transfer mode)-based Gigabit passive optical networking (GPON). During these years, it has become a hot topic that which will be more popular in broadband access and optical telecom applications, EPON or GPON? This article will compare these two technologies from the differences of architecture, bandwidth, efficiency, cost, etc.

Architecture

The biggest difference between the two technologies shows in architecture. EPON employs a single Layers 2 network that uses IP to carry data, voice, and video. While GPON provides three Layer 2 networks: ATM for voice, Ethernet for data, and proprietary encapsulation for voice.

EPON provides seamless connectivity for any type of IP-based or other "packetized" "communications". Since Ethernet devices are so popular and easy to get, implementation of EPONs can be highly cost-effective.

In GPON, virtual circuits are provisioned for different kinds of services sent from a central office primarily to business end users. This kind of transport provides high-quality service, but includes significant overhead because virtual circuits should be provisioned for each type of service. GPON equipment requires multiple protocol conversions, segmentation and reassembly (SAR), virtual channel (VC) termination and point-to-point protocol (PPP).

Bandwidth

EPON delivers symmetrical bandwidth of 1 Gbit/s. EPON's Gigabit Ethernet service actually constitutes 1 Gbit/s of bandwidth for data and 250 Mbit/s of bandwidth for encoding. GPON promises 1.25-Gbit/s or 2.5-Gbit/s downstream, and upstream bandwidths scalable from 155 Mbit/s to 2.5 Gbit/s. GPON's 1.25-Gbit service specifies a usable bandwidth of 1.25 Gbit/s, with no requirement for encoding. Gigabit Ethernet interfaces to the aggregation switch, central office, and metro are currently cost-effective to aggregate 1-Gbit ports for transport. But for 1.25 Gbit, there is no way.

Efficiency

Efficiency has to be considered in both directions of a PON. Each PON protocol introduces its own overhead in either direction. In the downstream direction, protocol overhead could be negligible. In the upstream direction, the total scheduling overhead within EPON is from 90.33 percent to 97.08 percent compared to a GbE point-to-point link. In the downstream direction, EPON efficiency reaches from 97.13 percent to 98.92 percent of the efficiency of a point-to-point 1GbE link, while GPON in GTC Encapsulation Method (GEM) mode can achieve ~ 95 percent efficiency of its usable bandwidth. The downstream EPON data rate can be doubled to 2.5Gbps comparable to GPON.

Cost

EPON simplifies the networks and needs no complex and expensive ATM and Sonet elements. Thus it helps lower the costs to subscribers. Now the cost of EPON equipment is about 10 percent of the costs of GPON equipment.

Encryption

Encryption is part of the ITU standard. EPON uses an AES-based mechanism, which is supported by multiple silicon vendors and deployed in the field. And EPON encryption is both downstream and upstream. However, GPON encryption is downstream only.

Ethernet Features

EPON is an IEEE Ethernet standard and uses Ethernet switches within its silicon, it can natively support all of the 802.1 and 802.3 Ethernet, including VLAN tags, prioritization, OAM, etc. All Ethernet services can be natively delivered in a manner identical to what is done with switched Ethernet today. As to GPON, it only defines the transport of Ethernet frames. So it has no native Ethernet functionality. Ethernet switches must be placed either in front of or within GPON OLTs and ONTs to provide any additional Ethernet capabilities.

EPON and GPON technologies have been introduced into the market because of service quality and price point. By comparing the differences of the two technologies, it shows EPON is a superior technology for delivering residential and small-to-medium enterprise Ethernet services in terms of its advantages in bandwidth, efficiency, cost, encryption and Ethernet features. So EPON will be employed in FTTH solution area in a large scale earlier and faster than GPON.

Originally published at http://www.streetarticles.com/internet-and-businesses-online/epon-vs-gponwhich-will-be-more-popular

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