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  • Introduction to Small Form-factor Pluggable (SFP) Transceiver Modules

    Introduction to Small Form-factor Pluggable (SFP) Transceiver Modules

    What Is SFP?
    SFP, short for small form-factor pluggable is a compact, hot-pluggable transceiver used for both telecommunication and data communications applications. SFP transceiver can be regarded as the upgrade version of GBIC module. Unlike GBIC with SC fiber optic interface, SFP is with LC interface and the main body size of SFP is only about half of GBIC so that it can save more space. SFP interfaces a network device mother board (for a router, switch, media converter or similar devices) to a fiber optic or copper networking cable. Meanwhile, SFP is a popular industry format supported by many network component vendors. It is designed to support SONET, Gigabit Ethernet, Fibre Channel, and other communications standards.

    The SFP transceiver is not standardized by any official standards body, but rather is specified by a Multi-source Agreement (MSA) among competing manufacturers. The SFP was designed after the GBIC interface, and allows greater port density (number of transceivers per cm along the edge of a mother board) than the GBIC, which is why SFP is also known as mini-GBIC. The related Small Form Factor transceiver is similar in size to the SFP, but is soldered to the host board as a through-hole device, rather than plugged into an edge-card socket.

    However, as a practical matter, some networking equipment manufacturers engage in vendor lock-in practices whereby they deliberately break compatibility with "generic" SFPs by adding a check in the device's firmware that will enable only the vendor's own modules. For example, in 2003 during a routine Internet Operating System (IOS) update on their Catalyst line of switches, Cisco added a feature that would cause the switch to reject optical modules that were not deemed "Cisco brand".

    Types of SFP Transceiver Modules
    SFP Transceivers are available with a variety of transmitter and receiver types, allowing users to select the appropriate transceiver for each link to provide the required optical reach over the available optical fiber type (e.g. multi-mode fiber or single-mode fiber).

    In the market, SFP transceiver modules are commonly available in several different categories:

    For multi-mode fiber, with black or beige extraction lever
    SX - 850 nm, for a maximum of 550 m at 1.25 Gbit/s (Gigabit Ethernet) or 150m at 4.25 Gbit/s (Fibre Channel)

    For single-mode fiber, with blue extraction lever
    LX - 1310 nm, for distances up to 10 km
    EX - 1310 nm,for distances up to 40 km
    ZX - 1550 nm, for distances up to 80 km
    BX - 1490 nm 1310nm, for distances up to 10 km
    1550 nm 40 km (XD), 80 km (ZX), 120 km (EX or EZX)

    For copper twisted pair cabling
    1000BASE-T - these modules incorporate significant interface circuitry and can only be used for Gigabit Ethernet, as that is the interface they implement. They are not compatible with (or rather: do not have equivalents for) Fibre channel or SONET.

    For WDM (Wavelength Division Multiplex) system
    BiDi SFP (Bidirectional SFP) for bi-directional traffic on a single fiber. Coupled with CWDM (Coarse Wavelength Division Multiplexing), these double the traffic density of fiber links
    CWDM and DWDM (Dense Wavelength Division Multiplexing) transceivers at various wavelengths achieving various maximum distances

     Applications of SFP Transceiver Module
    SFP is expected to perform at data speed of up to five gigabits per second (5Gbps), and possibly higher. Because SFP module can be easily interchanged, so electro-optical or fiber optic networks can be upgraded and maintained more conveniently than that with traditional soldered-in modules. Owing to its low cost, low profile and the ability to provide a connection to different types of optical fibers, SFP transceiver can result in a substantial cost savings, both in maintenance and in upgrading efforts. SFP transceiver is available with multi-mode single-mode fiber optics, allowing users to select the appropriate transceiver for each link in order to provide the required optical reach over the available optical fiber type. It is also available with copper cable interfaces, which allows a host device designed primarily for optical fiber communications to communicate over unshielded twisted pair networking cables. Modern optical SFP transceiver supports DDM (Digital Diagnostics Monitoring) functions, also known as DOM (Digital Optical Monitoring). This feature gives users the ability to monitor the real-time parameters of SFP transceiver, such as optical output power, optical input power, temperature, laser-bias current and transceiver supply voltage.

    Click on Link to buy Compufox SFP Transceivers

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  • Difference between UPC and APC fiber connectors

    Ever wonder what the difference is between ultra physical contact (UPC) and angled physical contact (APC) singlemode fiber connectors and which one to use? As usual, the answer is, “It depends.”

    Let’s take a closer look.

    8 Degrees of Separation


    The main difference between APC and UPC connectors is the fiber endface. APC connectors feature a fiber endface that is polished at an 8-degree angle, while UPC connectors are polished with no angle. UPC connectors are not exactly flat however; they have a slight curvature for better core alignment. Another more obvious difference is color. UPC adapters are blue while APC adapters are green.


    What does the difference mean? With UPC connectors, any reflected light is reflected straight back towards the light source. The angled endface of the APC connector causes reflected light to reflect at an angle into the cladding versus straight back toward the source. This causes some differences in return loss, which is a measurement of reflected light that is expressed as a negative dB value (the higher the value, the better). Industry standards recommend that UPC connector return loss should be -50dB or greater, while APC connector return loss should be -60dB or greater.

    UPC-APCRemember, return loss is different than insertion loss, which refers to the amount of optical power lost through a connector or cable length. Insertion loss is what we use to determine loss budgets. Achieving low insertion loss is typically easier with UPC connectors due to less air gaps than APC connectors. However, manufacturing techniques have improved significantly to create more precise angles on APC connectors and bring insertion loss down closer to that of UPC connectors. 

    Application Considerations


    There are some applications that are more sensitive to return loss than others that call for APC connectors. For example, in higher optical wavelength ranges (above 1500 nanometers) like those use for RF video signals, reflected light can adversely impact the signal. That is why we see APC connectors being used by most cable companies and other FTTX providers in outside plant applications.

    APC connectors are also commonly used in passive optical applications (both GPONs and passive optical LANs) due to the fact that many of these systems also use RF signals to deliver video. Future higher-speed passive optical networks and other WDM applications that will use higher wavelengths via singlemode fiber will also likely require the reduced return loss of APC connectors.

    One thing that should be noted is that APC and UPC connectors cannot and should not be mated. Not only does it cause poor performance since the fiber cores will not touch, but it can also destroy both connectors. The last thing you want to do is cause permanent transmitter damage—especially with higher-cost singlemode equipment.

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  • Migrate to a 40-Gbps Data Center with Cisco QSFP BiDi Technology

    What You Will Learn

    This document describes how the Cisco® 40-Gbps QSFP BiDi transceiver reduces overall costs and installation time for customers migrating data center aggregation links to 40-Gbps connections.

    As a result of data center consolidation, server virtualization, and new applications that require higher data transport rates, the data center network is shifting to 10 Gbps at the access layer and 40 Gbps at the aggregation layer. A broad portfolio of high-performance and high-density 10- and 40-Gbps Cisco Nexus® Family switches is available at attractive prices for this transition. However, to support 40-Gbps connectivity, data center architects are challenged by the need for a major upgrade of the cabling infrastructure, which can be too expensive or disruptive to allow data centers to quickly adopt and migrate to the 40-Gbps technology.

    Cisco solves this problem with innovative 40-Gbps Quad Small Form-Factor Pluggable (QSFP) bidirectional (BiDi) technology that allows reuse of existing 10-Gbps fiber infrastructure for 40-Gbps connections.

    Challenges with Existing 40-Gbps Transceivers

    Standard short-reach (SR) 10- and 40-Gbps transceivers use fundamentally different connectivity formats, requiring fiber cabling infrastructure to be redesigned and replaced. 10-Gbps SR transceivers operate over dual-fiber multimode fiber (MMF) with LC connectors, and 40-Gbps SR protocols, such as SR4 and CSR4, operate over MMF ribbon with MPO connectors. As a result, 40-Gbps MPO-based SR4 transceivers cannot reuse aggregation fiber infrastructure built for 10-Gbps connectivity.

    Connector type is not the only concern. Whereas 10-Gbps SR transceivers require 2 fiber strands per 10-Gbps link, 40-Gbps SR4 and CSR4 transceivers require a theoretical minimum of 8 fiber strands, and often 12 fiber strands in practice. The reason for this requirement is that 40-Gbps SR4 and CSR4 use 4 parallel fiber pairs (8 fiber strands) at 10-Gbps each for a total of 40-Gbps full duplex, as shown in Figure 1. However, both use MPO-12 connectors, which terminate 12-fiber ribbons. As a result, 4 fiber strands in each connection are unused and wasted.

    To economize trunk fiber in a structured cabling environment, a 2 x 3 MPO fiber conversion module could combine three SR4 links onto two 12-fiber ribbon cables. But even then the 40-Gbps SR4 trunk still uses 8 fiber strands per link compared to 2 fiber strands in the case of 10-Gbps SR.

    At best, the connector change and increased fiber density needed for SR4 require a significant cable plant upgrade, making it expensive and disruptive for customers to migrate from 10-Gbps connectivity to 40‑Gbps connectivity in their existing data centers.

    Figure 1.      Concept of Existing 40-Gbps Transceivers: Of the 12 Fiber Strands Terminated by MPO-12 Connectors, 8 Fiber Strands (4 Fiber Pairs) Carry Traffic and 4 Are Unused


    Solution with Cisco 40-Gbps QSFP BiDi Transceiver

    The Cisco QSFP BiDi transceiver, shown in Figure 2, transmits full-duplex 40-Gbps traffic over one dual-fiber LC-connector OM3 or OM4 MMF cable. It provides the capability to reuse 10-Gbps fiber infrastructure. In other words, it enables data center operators to upgrade to 40-Gbps connectivity without making any changes to the previous 10-Gbps fiber cable plant.

    Figure 2.      Cisco QSFP BiDi Transceiver (QSFP-40G-SR-BD)


    The Cisco QSFP BiDi transceiver has two 20-Gbps channels, each transmitted and received simultaneously over two wavelengths on a single MMF strand. The result is an aggregated duplex 40-Gbps link over a MMF duplex LC-terminated fiber cable. The connection can reach 100 meters on OM3 MMF or 150 meters on OM4 MMF, which is the same as 40-Gbps SR4. Figure 3 shows the technology concept of the Cisco QSFP BiDi transceiver.

    Most Cisco switching and routing products that support 40 Gigabit Ethernet interfaces support the Cisco QSFP BiDi transceiver. For a complete list of supporting products, refer to the Cisco 40 Gigabit Optical Transceiver product page at

    Figure 3.      Concept of Cisco QSFP BiDi Transceiver


    Savings with Cisco QSFP BiDi When Migrating from 10 Gbps to 40 Gbps

    This section presents two case studies that demonstrate the savings achieved by using Cisco QSFP BiDi technology for 40-Gbps connectivity in data center networks. The case studies show how Cisco QSFP BiDi technology can remove the cost barriers for migrating and expanding the existing 10-Gbps cabling footprint to 40-Gbps infrastructure to provide the higher data rate in the data center network.

    Case Study 1: 288 x 40-Gbps Connections with Unstructured Cabling

    In an unstructured cabling system, devices are connected directly with fiber cables. This direct-attachment design can be used to connect devices within short distances in a data center network. As shown in Figure 4, direct connection between two 40-Gbps devices can be provided by MMF cables with either QSFP SR4 or QSFP BiDi transceivers at two ends.

    Figure 4.      Direct 40-Gbps Connections


    The QSFP SR4 transceiver uses MPO-12 connectors, whereas Cisco QSFP BiDi uses LC connectors. Existing 10-Gbps connections commonly are MMF cables with LC connectors. Therefore, with QSFP SR4 transceivers, none of the existing 10-Gbps MMF cables can be reused because the connector types are different. Cisco QSFP BiDi allows cable reuse, resulting in zero-cost cabling migration from direct 10-Gbps connections to direct 40-Gbps connections.

    Table 1 summarizes the costs and savings of migration and new deployment of 288 direct connections. To migrate the existing 288 10-Gbps connections to 40-Gbps connections, Cisco QSFP BiDi does not require any new spending on cables. Therefore, in comparison to QSFP SR4 transceivers, Cisco QSFP BiDi transceivers reduce costs by 100 percent and provide savings of up to US$290 per 40-Gbps port.

    Table 1.       Fiber Infrastructure Savings for 10-Gbps to 40-Gbps Direct-Cabling Migration and New 40-Gbps Deployment

    Fiber Cable Infrastructure Cost and Savings with BiDi* (US$)




    288 LC-connector dual-fiber MMF cables for Cisco BiDi




    288 MPO-connector ribbon-fiber MMF cables for SR4




    10-Gbps to 40-Gbps migration

    Total savings (US$)




    Per port savings (US$)




    Savings (percent)




    New 40-Gbps deployment

    Total savings (US$)




    Per-port savings (US$)




    Savings (percent)




    * This example is based on real-world cable cost estimates. The transceiver cost is not included.

    For the case in which 288 new direct 40-Gbps connections are needed in addition to the existing cabling infrastructure for a data center migration or expansion, the savings for 288 new connections using Cisco QSFP BiDi instead of QSFP SR4 transceivers is as high as 77 percent and US$221 per 40-Gbps port. These numbers do not take into account the installation costs. Adding installation costs could easily double the SR4 deployment costs.

    Case Study 2: 384 x 40-Gbps Connections with Structured Cabling

    A structured cabling system is commonly deployed in data center networks to provide flexible and scalable cabling infrastructure. Structured cabling uses short patch cords to attach devices to a patch panel and then runs fiber trunks either to consolidate the cables in a central location for additional connectivity or to direct them to another patch panel to which the remote devices are attached. Figure 5 shows a simple example of a 10-Gbps structured cabling design.

    Figure 5.      Simple Example of 10-Gbps Structured Cabling


    For migration of a data center with a structured 10-Gbps cabling system, Cisco QSFP BiDi technology allows you to repurpose the existing cabling system - including the patch cables, patch panels with MTP/MPO LC modules, and fiber trunks - for 40-Gbps connectivity. In contrast, QSFP SR4 transceivers require new patch cables and patch panels because the connector types differ and the size of the fiber trunk needs to be quadrupled.

    This case study examines a simple nonblocking two-tier fabric design (Figure 6) that provides 1536 10-Gbps edge ports on its leaf layer. Its spine layer is composed of two Cisco Nexus 9508 Switches, and its leaf layer consists of 32 Cisco Nexus 9396PX Switches, each with six 40-Gbps links to every spine Cisco Nexus 9508. There are 384 40-Gbps links total between the leaf and spine layers.

    Figure 6.      Two-Tier Network Example


    If 384 x 10-Gbps connections are to be reused to construct this network, no additional spending on cabling will be needed if Cisco QSFP BiDi transceivers are used for all the 40-Gbps links. This scenario thus offers a 100 percent cost savings compared to the cost of reconstructing the cabling system using QSFP SR4 transceivers, including the cost of new patch cables, new patch panels, and expansion of the current fiber trunk.

    If the cabling for this network is a new (greenfield) deployment or an expansion of an existing cabling system, the 384 x 40-Gbps connections can be built by using MMF cables and either QSFP SR4 transceivers or Cisco QSFP BiDi transceivers. Figures 7 and 8 show design examples for each option. Table 2 compares real-world cost estimates for these two designs. The design with Cisco QSFP BiDi offers 77 percent savings over that with QSFP SR4 transceivers, which is equivalent to a savings of US$2077 per 40-Gbps connection.

    Figure 7.      Structured 40-Gbps Cabling with QSFP SR4 Transceivers


    Table 2.       Structured 40-Gbps Cable Infrastructure Cost Comparison

    Structured 40-Gbps Cable Infrastructure Cost Savings with BiDi Technology (US$)


    Unit Price* (US$)


    Total (US$)

    90m 12-fiber MPO-MPO trunk cable (3 SR links per 2 cables)


    384 x (2/3)


    12-fiber MPO-MPO 2x3 conversion module (3 SR links per module, both ends)


    384 x (1/3) X 2


    12-fiber MPO jumper (1 per link, both ends)


    384 x 2


    SR total




    90m 12-fiber MPO-MPO trunk cable (6 BiDi links per cable)


    384 x (1/6)


    12-fiber MPO-LC trunk module (6 BiDi links per module, both ends)


    384 x (1/6)


    12-fiber LC jumper (1 per link, both ends)


    384 x 2


    BiDi total




    Total savings




    Percentage savings




    *Based on manufacturer’s list price
    Figure 8.      Structured 40-Gbps Cabling with Cisco QSFP BiDi Transceivers



    Cisco QSFP BiDi technology removes 40-Gbps cabling cost barriers for migration from 10-Gbps to 40-Gbps connectivity in data center networks. Cisco QSFP BiDi transceivers provide 40-Gbps connectivity with immense savings and simplicity compared to other 40-Gbps QSFP transceivers. The Cisco QSFP BiDi transceiver allows organizations to migrate the existing 10-Gbps cabling infrastructure to 40 Gbps at no cost and to expand the infrastructure with low capital investment. Together with Cisco Nexus 9000 Series Switches, which introduce attractive pricing for networking devices, Cisco QSFP BiDi technology provides a cost-effective solution for migration from 10-Gbps to 40-Gbps infrastructure.

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  • Straight-through, Crossover, and Rollover Wiring

    When talking about cable pinouts we often get questions as to the difference in Straight-through, Crossover, and Rollover wiring of cables and the intended use for each type of cable. These terms are referring to the way the cables are wired (which pin on one end is connected to which pin on the other end). Below we will try shed some light on this commonly confused subject.


    Straight-Through Wired Cables

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  • Feds get huge response to request for IoT input

    By Sean Kinney



    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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