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  • OTDR (Optical Time Domain Reflectometer) Dead Zone Tutorial

     

    OTDR (Optical Time Domain Reflectometer) is a familiar fiber test instrument for technicians or installers to characterize an optical fiber. To understand the specifications which may affect the performance of OTDR can help users get maximum performance from their OTDRs. This tutorial will introduce one of the key specifications—Dead Zone.

    What Is a Dead Zone?

    The OTDR dead zone refers to the distance (or time) where the OTDR cannot detect or precisely localize any event or artifact on the fiber link. It is always prominent at the very beginning of a trace or at any other high reflectance event.

    OTDR_Trace
    Why makes a Dead Zone occur?

    OTDR dead zone is caused by a Fresnel reflection (mainly caused by air gap at OTDR connection) and the subsequent recovery time of the OTDR detector. When a strong reflection occurs, the power received by the photodiode can be more than 4,000 times higher than the backscattered power, which causes detector inside of OTDR to become saturated with reflected light. Thus, it needs time to recover from its saturated condition. During the recovering time, it can not detect the backscattered signal accurately which results in corresponding dead zone on OTDR trace. This is like when your eyes need to recover from looking at the bright sun or the flash of a camera. In general, the higher the reflectance, the longer the dead zone is. Additionally, dead zone is also influenced by the pulse width. A longer pulse width can increase the dynamic range which results in a longer dead zone.

    OTDR connection
    Event Dead Zones & Attenuation Dead Zone

    In general, dead zones on an OTDR trace can be divided into event dead zone and attenuation dead zone.

    OTDR_dead_zone
    Event Dead Zone

    The event dead zone is the minimum distance between the beginning of one reflective event and the point where a consecutive reflective event can be detected. According to the Telcordia definition, event dead zone is the location where the falling edge of the first reflection is 1.5 dB down from the top of the first reflection.

    EDZ
    Attenuation Dead Zone

    The attenuation dead zone is the minimum distance after which a consecutive non-reflective event can be detected and measured. According to the Telcordia definition, it is the location where the signal is within 0.5 dB above or below the backscatter line that follows the first pulse. Thus, the attenuation dead zone specification is always larger than the event dead zone specification.

    ADZ

    Note: In general, to avoid problems caused by the dead zone, a launch cable of sufficient length is always used when testing cables which allows the OTDR trace to settle down after the test pulse is sent into the fiber so that users can analyze the beginning of the cable they are testing.

    The Importance of Dead Zones

    OTDR_testThere is always at least one dead zone in every fiber—where it is connected to the OTDR. The existence of dead zones is an important drawback for OTDR, specially in short-haul applications with a large number of fiber optic components. Thus, it is important to minimize the effects of dead zones wherever possible.

    As mentioned above, dead zones can be reduced by using a lower pulse width, but it will decrease the dynamic range. Thus, it is important to select the right pulse width for the link under test when characterizing a network or a fiber. In general, short pulse width, short dead zone and low power are used for premises fiber testing and troubleshooting to test short links where events are closely spaced, while a long pulse width, long dead zone and high power are used for long-haul fiber testing and communication to reach further distances for longer networks or high-loss networks.

    The shortest-possible event dead zone allows the OTDR to detect closely spaced events in the link. For instance, testing fibers in premises networks (particularly in data centers) requires an OTDR with short event dead zones since the patch cords of the fiber link are often very short. If the dead zones are too long, some connectors may be missed and will not be identified by the technicians, which makes it harder to locate a potential problem.

    Short attenuation dead zones enable the OTDR not only to detect a consecutive event but also to return the loss of closely spaced events. For instance, the loss of a short patch cord within a network can now be known, which helps technicians to have a clear picture of what is actually inside the link.

    Summary

    OTDR is one of the most versatile and widely used fiber optic test equipment which offers users a quick, accurate way to measure insertion loss and shows the overview of the whole system you test. Dead zone, with two general types, is an important specification of OTDR. It is necessary for users to understand dead zone and select the right configuration in order to get maximum OTDR performance during test. In addition, OTDRs of different brands are designed with different minimum dead zone parameters since manufacturers use different testing conditions to measure the dead zones. Users should choose the suitable one according to the requirements and pay particular attention to the pulse width and the reflection value.

     

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  • Identify Types of Network Cables and Connectors

    There are three types of network cables: fiber, twisted pair, and coaxial.

    Fiber is the most expensive of the three and can run the longest distance. A number of types of connectors can work with fiber, but three you must know are SC, ST, and LC.

    Twisted pair is commonly used in office settings to connect workstations to hubs or switches. It comes in two varicties: unshielded (UTP) and shielded (STP), The two types of connectors commonly used are RJ-11 (four wires and popular with telephones), and RJ-45 (eight wires and used with xBaseT networks—100BaseT, 1000BaseT, and so forth). Two common wiring standards are T568A and T568B.

    Coaxial cabling is not as popular as it once was, but it's still used with cable television and some legacy networks. The two most regularly used connectors are F-conectors (television cabling) and BNC (10Base2, and so on).

    Fiber

    Fiber-optic cabling is the most expensive type. Although it's an excellent medium, it's often not used because of the cost of implementing it. It has a glass core within a rubber outer coating and uses beams of light rather than electrical signals to relay data. Because light doesn't diminish over distance the way electrical signals do, this cabling can run for distances measured in kilometers with transmission speeds from 100 Mbps up to 1 Gbps higher.

    Fiber optic cable

    Often, fiber is used to connect runs to wiring closets where they break out into UTP or other cabling types, or as other types of backbones. Fiber-optic cable can use either ST, SC, or LC connector. ST is a barrel-shaped connector, whereas SC is squared and easier to connect in small spaces.The LC connector looks similar to SC but adds a flange on the top (much like an RJ-45 connector) to keep it securely connected.

    st sc lc connectors

    Note: In addition to these listed in the A + objectives, other connectors are used with fiber. FC connectors may also be used but are not as common. MT-RJ is a popular connector for two fibers in a small form factor.

    Twisted Pair

    There are two primary types of twisted-pair cabling (with categories beneath cach that are shielded twisted pair (STP) and unshielded twisted pair (UTP). In both cases, the cabling is made up of pairs of wires twisted around each other.

    UTP offers no shielding (hence the name) and is the network cabling type most prone to outside interference. The interference can be from a fluorescent light ballast, eletrical motor, or other such source (known as eletromagnetic interference [EMI]) or from wires being too close together and signals jumping across them (known as crosstalk), STP adds a foil shield around the twisted wires to protect against EMI.

    Twisted Pair

    STP cable uses IBM data connector (IDC) or universal data connector (UDC) ends and connects to token ring networks. While you need to know STP for the exam, you are not required to have any knowledge of the connectors associated with it. You must, however, know that most UTP cable uses RJ-45 connectors, which look like telephone connectors (RJ-11) but have eight wires instead of four.

    RJ-45 connectors

    Two wiring standards are commonly used with twisted-pair cabling:T568A and T568B (sometimes referred to simply as 568A and 568B). These are telecommunications standards from TIA and EIA that specify the pin arrangements for the RJ-45 connectors on UTP or STP cables. The number 568 refers to the order in which the wires within the Category 5 cable are terminated and attached to the connector. The signal is identical for both.

    T568A was the first standard, released in 1991. Ten years later, in 2001, T568B was released. Pin numbers are read left to right, with the connector tab facing down. Notice that the pin-outs stay the same, and the only difference is in the color coding of the wiring.

     

    Pin assignments for T568A and T568B

    Note: Mixing cables can cause communication problems on the network. Before installing a network or adding a new component to it, make sure the cable being used is in the correct wiring standard.

    Coaxial

    Coaxial cable, or coax, is one of the oldest media used in networks. Coax is built around a center conductor or core that is used to carry data from point to point. The center conductor has an insulator wrapped around it, a shield over the insulator, and a nonconductive sheath around the shielding. This construction allows the conducting core to be relatively free from outside interference. The shielding also prevents the conducting core from emanating signals externally from the cable.

    Note: Before you read any further, accept the fact that the odds are incredibly slim that you will ever need to know about coax for a new installation in the real world (with the possible exception of RG-6, which is used from the wall to cable modem). If you do come across it, it will be in an existing installation and one of the first things you'll recommend is that it be changed. 

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  • How to Install or Remove SFP Transceiver Modules on Cisco Device

    The SFP (small form Factor pluggables) transceiver modules are hot-pluggable I/O devices that plug into module sockets. The transceiver connects the electrical circuitry of the module with the optical or copper network. SFP transceiver modules are the key components in today's transmission network. Thus, it is necessary to master the skill of installing or removing a transceiver modules to avoid unnecessary loss. This tutorial are going to guide you how to install or remove SFP transceiver module in a right way.

     

    Things you should Know Before Installing or Removing SFP

    Before removing or installing a Transceiver Module you must disconnect all cables, because of leaving these attached will damage the cables, connectors, and the optical interfaces. At the same time please be aware that do not often remove and install an SFP transceiver and it can shorten its useful life. For this reason transceivers should not be removed or inserted more often than is required. Furthermore, transceiver modules are sensitive to static, so always ensure that you use an ESD wrist strap or comparable grounding device during both installation and removal.

     

    Required Tools

    You will need these tools to install the SFP transceiver module:
    Wrist strap or other personal grounding device to prevent ESD occurrences.Antistatic mat or antistatic foam to set the transceiver on.Fiber-optic end-face cleaning tools and inspection equipment

     

    Installing SFP Transceiver Modules

    SFP transceiver modules can have three types of latching devices to secure an SFP transceiver in a port socket:
    SFP transceiver with a Mylar tab latch.SFP transceiver with an actuator button latch.SFP transceiver that has a bale-clasp latch.
    Types of SFP Latching

    Determine which type of latch your SFP transceiver uses before following the installation and removal procedures.

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  • Feds get huge response to request for IoT input

    By Sean Kinney   www.industrialiot5G.com

     

     

    More than 100 companies suggest ways U.S. government can help advance the IoT

    Many industry watchers feel the U.S. is slipping behind other countries, particularly Germany and China, in creating a unified national strategy for development of the Internet of Things or IoT. But federal leaders, in the early stages of involvement, reached out to the telecom industry for guidance.

    Back in April the National Telecommunications and Information Administration, a part of the U.S. Department of Commerce, issued a “request for comments on the benefits, challenges and potential roles for the government in fostering the advancement of the Internet of Things.”

    Two months later and the call for comment has been met in spades with more than 130 filings coming from a broad swath of telecom interests including carriers like AT&T, T-Mobile, Verizon and Vodafone; vendors including Nokia, Ericsson, Huawei and Samsung; and industry trade groups like the Wi-Fi Alliance, Wireless Infrastructure Association, the Open Connectivity Foundation and the GSMA.

    Here’s a full list of the respondents and their filings with NTIA. A review of some of the filings indicates a strong industry expectation that the rapid uptake of IoT will require global coordination and will likely create new markets while disrupting existing ones.

    Verizon representatives told NTIA: “To support this explosion of IoT devices, a robust and secure underlying communications network must serve as a foundation. That network requires both increased commercial spectrum and development of the underlying core infrastructure. We encourage all stakeholders to work together to ensure that these necessary building blocks for IoT development are available and accessible. To enable sufficient spectrum to power this new wave of connected innovation, private and public sectors must continue to cooperate, not only to develop more ways to effectively share spectrum, but also to provide federal users incentives to free up spectrum for commercial licensed and unlicensed use. As potentially billions of new IoT devices are deployed, they will drive data growth that – combined with the parallel growth in overall data usage by consumer devices – will require new commercial spectrum allocations to accommodate the unprecedented demands for more bandwidth. This includes spectrum necessary to support 5G, since 5G’s super-fast speeds and low latency will help facilitate new IoT use cases.”

    Ericsson commented: “In Ericsson’s view, 5G is the technology that will unleash the true potential of the Internet of Things. To support the IoT’s development, the government should unleash the resources that will ensure U.S. leadership in 5G by releasing more spectrum for commercial use. Through network slicing, 5G technology will allow a single infrastructure to meet the very different needs of Massive and Critical IoT devices – it will enable networks to handle the incredible increase in data from the billions of low energy, low data devices, while also providing very high reliability, availability and security for critical uses. We also encourage the government to support global standards and best practices and to allow industry to continue to innovate and coalesce around the most favorable IoT solutions.”

    And from the GSMA’s point of view: “The United States should forbear from regulating IoT and avoid reflexively extending legacy regulations designed for outdated technologies to the IoT…The U.S. government should support and promote industry alignment around interoperable, industry-led specifications and standards across the global IoT ecosystem…The U.S. government should promote the allocation of globally harmonized spectrum that can support IoT…The U.S. government should encourage industry to build trust into IoT devices. Existing laws and regulations, operating in tandem with self-regulatory regimes and best practices, will provide sufficient protection to consumers as the IoT develops…Finally, the U.S. government should engage on a bilateral and multilateral basis, as appropriate, to ensure that international IoT activities similarly encourage competition, investment, and innovation. Regulatory interference at this stage—from any source—could lead to fragmentation and impede innovation, inhibiting the IoT’s ability to reach its full potential to deliver benefits to consumers.”

     

     

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  • Atari bringing back devices with Sigfox IoT agreement

    By Tim Skinner           Telecoms.com

    Retro gaming giant Atari will soon be entering the IoT arena following a partnership with Sigfox, the low power WAN provider. Famed for its trailblazing old-school computers and gaming consoles in the 1980s and 1990s, an announcement from Atari said it will soon be developing and launching consumer IoT services. While tangible details weren’t particularly forthcoming, and won’t be for the time being, Atari did hint at a move back to hardware having been primarily, if not solely, focused on software and gaming for the best part of the last 20 years. Atari said the initial product line will include offerings in areas such as home, pets, lifestyle and safety. By combining with Sigfox, Atari plans on developing a wide range of new products, from the very simple to the highly sophisticated, which users can track at any time. Sigfox says that by connecting to its network, products will benefit from an extended battery life and no need for paring or connectivity configuration. “By partnering together and using SIGFOX’s dedicated IoT connectivity, we are going to create amazing products with our brand,” said Fred Chesnais, Chief Executive Officer, Atari. “We look forward to our collaboration with SIGFOX and releasing new products to the mass market on a global scale.” It’s fair to assume Atari is targeting a move back into hardware and away from gaming, although more information will be released in due course. Atari says development of the new product line will begin in 2016.

     

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