How Do Network Cable Testers Work? (Dan Klimke)

Network cable testers are essential tools for engineers or technicians to ensure the connectivity and reliability of wired ethernet networks. In this comprehensive guide, we will explore how network cable testers work. We will also discuss how to detect, localize, and resolve common faults and issues, plus the difference between network cable testers and ethernet network testers.

● What is a Network Cable Tester?

● What are the types of Network Cable Testing?

● Detecting and Localizing Faults with a Network Cable Tester

● The Difference between a Network Cable Tester and an Ethernet Network Tester

● Conclusion

What is a Network Cable Tester?

A network cable tester is a specialized tool that network technicians rely on to assess the functionality and integrity of network cabling. Its primary purpose is to verify the physical connections and wiring within a network infrastructure, ensuring proper installation for optimal data transmission. It is important to know the key differences between the types of cable testers and technologies available, and which is appropriate for your requirements. (Note, this article focuses on testing twisted-pair copper cabling; fiber optic testing is another subject.)

Three Types of Network Cable Testing – Validation, Qualification, Certification

Validation – Basic Cable Testing

Validating or verifying cabling is the most essential form of cable testing in which the connectivity of the individual wires is examined. The simplest form of tester in this category may rely on having a remote terminator at the far end; an electrical pulse is sent down the wire in order to identify common issues such as breaks (or “opens”), shorts (miswiring where one conductor contacts another), and improper continuity (sometimes called “wiremap”). Wiremapping ensures that each conductor is correctly terminated to the correct pins in plugs or jacks.

More sophisticated testers use a technology called Time Domain Reflectometry (TDR) where an electrical pulse is injected into cabling which is open or unterminated at the far end. By measuring and interpreting the electrical reflections coming back to the tester (and the timing of the signal), it is able to determine various faults and the distance to them as well as the overall length of the cable. (Accurate length and distance to fault measurements require the user to enter the type of cabling under test. The “speed” of the cable – referred to as its Nominal Velocity of Propagation (NVP) – must be taken into account for accurate length and distance measurements.)

Qualification – What bandwidth will the cabling support?

Validating connectivity and proper wiring is essential, but do you know whether your cabling is of sufficient quality to provide the bandwidth required? With the insatiable growth in bandwidth demands, increasing speeds of Wi-Fi Aps (with Multi-Gig 2.5/5Gbps backhauls), and 1Gbps to 10Gbps infrastructure upgrades, network professionals must have confidence that their network will transport that data error-free at the maximum speed possible. Downtime or intermittent loss and errors is simply not an option.

To “qualify” a cable plant is to assess its ability to carry data at a particular speed or rate, error free. The most reliable and meaningful test methodology is to generate and measure the transmission of line rate Ethernet frames point-to-point over your network cabling infrastructure, qualifying its ability to support 100M/1G/2.5G/5G/10G on copper links. To do so, two testers are typically used, one at each end of the network under test. A pre-configured rate of network traffic is generated both upstream and downstream simultaneously, measured at each end. (These types of testers typically also include basic cable validation features as well.)

Running this type of test over a long duration (up to 24 hours) serves as a “soak test” to identify the presence of intermittent issues and noise events that can corrupt network traffic.

The other type of cable qualification tester is one that utilizes electrical signal parametrics (measurements such as insertion or return loss, near-end and far-end crosstalk, etc.) and compares those results against the specifications of a particular cabling standard, such as TIA-568-C.2 or ISO/IEC 11801. For example, if the test results are within the parameters of the standard’s requirements for Category 6A cabling, one can infer that the cabling will support 10Gbps.

But beware! Just because a cable does not meet the requirements of a standard does not mean that the cabling cannot support the transmission of packets at speed, error free. Many network owners have spent thousands in re-cabling links that did not meet the standard, but which could still carry multiple gigabits of network traffic. In fact, depending on the quality of installation and other parameters (such as lengths <100 meters), even Category 3 cabling can support 1 Gbps or better! Qualifying your cable plant by transmitting actual packets could save you from costly, unnecessary upgrades.

Certification – Does the cabling meet the requirements of a particular standard?

The only way to ensure that a cable plant complies with an industry standard is to use a tester that is capable of certification, comparing measurement results with the requirements as set out by the Telecommunications Industry Association (TIA) or International Standards Organization (ISO). The test results will show either a “pass” or “fail” against the requirements of the standard employed. No data frames are utilized in this methodology; specific electrical signaling and parametric measurements are compared to the standard’s specifications. Typical cable certification testers can be very expensive, single-purpose tools – making them cost-prohibitive for many installers and end-users.

How to use a network cable tester

Technicians connect the tester to the end of the cable being tested (and terminate at the far end if required.) The tester then sends signals through the cable and analyzes the responses received. This process helps identify common issues such as breaks (opens) in the cable, unintended connections (shorts), incorrect wiring, and problems related to cable length and signal quality.

By accurately identifying these faults, network cable testers enable technicians to locate the exact source of the problem. This information is invaluable for efficient troubleshooting and allows technicians to take appropriate actions to resolve the issues promptly.

By utilizing a network cable tester to validate an installation or adds, moves, and changes, technicians can ensure the overall performance and reliability of network cables. Properly installed and tested cables minimize the risk of network connectivity issues, data transmission errors, and downtime. This leads to improved network efficiency, reduced troubleshooting time, and increased productivity.

Features of Network Cable Testers

Network cable testers offer a range of features to enhance their functionality:

● Connectivity Testing: Network cable testers are designed to test the connectivity of the cables. They can check if a properly wired connection is available from one end of the cable to the other. Some advanced models can even measure the cable length, identify open circuits, short circuits, or reversed connections.

● Cable Locating: Basic cable testers typically also include the ability to inject an analog or digital “tone” onto the wire which can be detected and audibly amplified by a receiver called a probe (or “tone probe”). This is used to locate cable runs and to identify individual cables inside bundles in trays or equipment racks.

● Power over Ethernet (PoE) Measurement: There are two levels of PoE validation. Inexpensive testers are capable of reporting the presence and voltage of PoE supplied by a PSE (power sourcing equipment), but only more sophisticated testers are capable of load testing, that is, measuring the actual power (in watts) that the PSE is actually delivering. This is the only way to ensure that a PD (powered device) will have enough power to successfully operate, and that a switch’s PoE budget has not been maxed out.

● Network Link Testing: Some cable testers also feature the ability to detect ethernet link pulse and, in some cases, actually link to the network. The distinction between link DETECTION and the speed at which the tester can actually connect to the network is very important (see “Ethernet Network Tester” below.)

● Signal Strength Analysis: Testers with link detection may also come with features that allow them to analyze the signal strength on the network cable. In some cases, this is reporting the strength of the link pulse signal; this could include signal-to-noise ratio (SNR) and delay skew between pairs, essential measurements for multi-gig links (2.5 and 5Gbps.)

Detecting and Localizing Faults with a Network Cable Tester

Network cable testers are capable of detecting various faults and issues that can impact network performance. Common errors include opens, shorts, incorrect wiring, and incorrect cable lengths. Using a network cable tester, these faults can be localized, enabling technicians to respond quickly and efficiently.

By utilizing the tester's features, such as wire mapping, length measurement, and signal quality analysis, network technicians can identify the exact location and nature of the fault. This facilitates targeted troubleshooting and minimizes downtime.

The Difference between a Network Cable Tester and an Ethernet Network Tester

A network cable tester is aimed at diagnosing potential problems at the physical layer. It identifies a wide range of wiring faults, such as shorts, open wires, crossed pairs, and reversed pairs in ethernet cables. Additional features of advanced models may include the ability to measure cable length and trace the distance to faults.

While the network cable tester verifies the physical integrity of the ethernet cable connections that play a critical role in network reliability, the ethernet network tester focuses on ensuring operational performance and diagnosing higher-level network issues.

Actual link testing is the job of an ethernet network tester – a more sophisticated tool designed to test and evaluate the performance and functionality of ethernet-based networks. It measures data transmission, checks error rates, and assesses the operations of switches, routers and other integral components within the network's infrastructure including key services such as DHCP and DNS. This can also include network cable testing but is not always included.

While some cable testers may include the ability to detect ethernet link pulse, that is, to identify whether or not the cabling is connected to an active port, be aware that link “detection” is not the same as actively linking to the network. It is simply the ‘decoding’ and reporting the type of link pulse it sees on the wire. Even certain network testers may claim “10Gbps capable” when in fact, they are not able to actively link at that speed – simply detecting that the link partner is capable of connecting at that rate is not the same as validating that capability. Only by actually linking and communicating at the necessary speed ensures that a specific network link is operating at the highest possible configuration.

Acting as a full-functioning network client, network testers will also validate the availability and function of key network services such as DHCP and DNS, ensuring that other connected clients can get a valid IP address and resolve network addresses (URLs).

To ensure full connectivity at higher layers, the network tester may also be able to ping other devices on the local network or at remote sites, and/or conduct TCP/IP connectivity testing to assure the successful operation of specific applications and ports across the network infrastructure.

Additional functions of more sophisticated network testers can include packet capture, network discovery, path analysis, performance testing, remote control, and more.

NetAlly's LinkRunner AT: An Advanced Solution for Ethernet Network Testing

NetAlly's LinkRunner AT is a handheld ethernet network tester that includes cable testing, purposefully engineered to make the testing processes faster and more efficient. The device is equipped with advanced features, such as actively testing network linking at 1Gbps, identifying the link partner (switch port), and confirming reachability of internal network servers and/or external internet sites and validating key services (DHCP, DNS) capabilities that go well beyond the scope of basic cable testers by verifyingthe functionality and connectivity of the broader ethernet network.

The LinkRunner AT stands out due to its user-friendly interface and ability to rapidly detect and troubleshoot network issues. It provides detailed reports, allowing for better documentation. Test results can be automatically uploaded to the Link-Live reporting and analysis platform to improve collaboration between network engineers and technicians, creating greater job visibility, project control, and fleet management. Request a free virtual demo to learn more.

Conclusion

Network Cable Testers are fundamental tools for maintaining the connectivity of wired networks. As dedicated devices for assessing the quality and integrity of connections within a network infrastructure, they play a key role in ensuring consistent and efficient data transmission.

These testers probe into the detail of each network cable, checking for errors that might affect the network performance such as: open connections, shorts, incorrect wiring, and even problems related to the length and quality of signal transmission. By isolating these physical issues, network cable testers not only assist in a quick and accurate fault detection but also enable more efficient physical layer problem resolution.

The indispensability of these tools stems from their ability to precisely map the fault source, which aids targeted troubleshooting and minimizes network downtime. Advanced network cable testers stand out with enhanced features such as wire mapping, deeper connectivity testing, and signal strength analysis, furnishing technicians with a nuanced view of the network cable health. However they are not the only factor for a healthy network

While network cable testers are crucial for verifying the physical robustness of network cables, the comprehensive overview provided by ethernet network testers, such as NetAlly's LinkRunner AT, complements their functionality. The LinkRunner AT offers both – essential cable testing AND in-depth network diagnostics that go beyond basic physical connections, providing a more complete picture of overall network health and connectivity. This results in enhanced network management, and improved performance and reliability.

DAN KLIMKE

Director, Product Marketing

Dan Klimke serves as the Director of Marketing for NetAlly (www.netally.com). He has been involved in the premise cabling and network performance analysis segments of the network communications business for the past 30 years and is responsible for brand and product management as well as field and channel marketing at NetAlly, a leading provider of network analysis and troubleshooting solutions.

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