Test unshielded Cat 5e twisted pairs and Ethernet connections (2023)

Cat 5e (Enhanced) cables are commonly used in local area networks (LAN), telephones and videos. It is well suited for applications requiring unshielded twisted pair (UTP) and telephone zone cabling in a star configuration. Two phone lines can work and two additional pairs are available for future use. Using modular RJ-45 connectors, a Cat-5e installation enables 10BASE-T, 100BASE-T, 1000BASE-T, and 10GBASE-T at speeds of 10Mbps, 100Mbps, 1Gbps, and 10Gbps /s with acceptable performance up to 100m between active repeaters. Crimp connectors should be used for Ethernet LAN lines, but the small blue wire nuts will suffice for phone lines.

Cat 5e typically consists of four twisted pairs, each with a slightly different twist rate ranging from 50 to 75 turns/m to prevent crosstalk. The twisted pair used in Ethernet along with differential signaling minimizes external noise significantly, as common mode rejection eliminates the unwanted current induced equally on both conductors. Good performance requires keeping torque as close to the extremes as possible. Therefore, RJ-45 crimp leads are very suitable. (Cat 6a has a higher twist rate and better performance, but is not used in most LAN installations due to its higher cost.)

Test unshielded Cat 5e twisted pairs and Ethernet connections (1)

There are two termination standards, T568A and T568B. Using either of these patterns at both ends results in what is known as a straight cable configuration. Using T568A and T568B at the other end results in a crossover configuration. The choice of straight-through or crossover terminations depends on the type of equipment present at both ends. The difference lies in the positions of the two pins used for sending and the two pins used for receiving. The network will not work if transmission and reception are not connected.

(Video) Ethernet Cables, UTP vs STP, Straight vs Crossover, CAT 5,5e,6,7,8 Network Cables

Test unshielded Cat 5e twisted pairs and Ethernet connections (2)

Hubs and switches have MDI-X ports with internal crossovers. Routers, servers, and end hosts such as PCs all have uplink ports. When connecting devices with the same port type, a crossover cable is used. A straight cable is used when connecting devices with different port types. (Connecting a computer to a hub or switch requires a straight-through cable. Connecting two computers, switches, or hubs requires a crossover cable.) In fact, the devices manufactured today automatically detect and implement the appropriate settings , so that the cables can be used interchangeably. But it is best if the correct type is labeled and used in case a device is replaced in the future.

Short patch cords of any type are readily available. On long runs, particularly those that will be obscured with painted surfaces or fished through existing cavities, it is common practice to run the cable first and then connect both ends. Copper cables are available with stranded or solid conductors. Braid is generally used for patch cords when greater flexibility is desired, and solid is preferred for permanent installations.

In LANs, metropolitan area networks (MANs), and wide area networks (WANs), Ethernet is by far the dominant technology. In the past, coaxial and other cables were used, but today you see high-quality cables, mostly unshielded twisted pair (UTP) category 5e or fiber optic cables. The exception is wireless transmission. Whether the medium is wired or Wi-Fi, Ethernet packets are generated, transmitted, and processed in the same way. Wi-Fi is much preferred in home and commercial applications because it's fast, easy, and eliminates the clutter of cables and plumbing at the expense of a slightly less stable connection and the need for password protection.

(Video) Shielded vs Unshielded Ethernet Cable

An Ethernet transmission consists of short segments called frames. The source and destination addresses are given in each field. Defective frames are detected, discarded and replaced. Each Ethernet frame contains 48-bit MAC addresses that identify the source and destination. These elements create link-level connections. A recipient reads the destination address to determine whether the transmission is relevant or should be ignored. All of this is backward compatible, so new generation devices can be used in existing networks. The frame format does not change.

Earlier computers required an external network card, but today a network interface is part of the computer's motherboard. Modern Ethernet stations communicate via switches that transport Ethernet packets to the correct destination. Collisions are greatly reduced and only occur when the station and switch attempt to communicate simultaneously. Collisions are limited to a single link. Also, full-duplex communication was introduced in the 10Base-T standard and is used in Fast Ethernet and Gigabit networks. These implementations are completely free of data collisions.

When building a data network, an important final step is to test and certify it. Dedicated test equipment is available for use with fiber optic and optical media.

(Video) Wire Mapping: reversed, crossed, split, open, & short

Test unshielded Cat 5e twisted pairs and Ethernet connections (3)

An optical time domain reflectometer (OTDR) is used to test and evaluate fiber optic links. The instrument injects pulses of light into one end of the fiber under test and, at the same end, captures reflected light from one or more points on the link. Return pulses are measured and timed so that the location of anomalies and other relevant data can be known.

A desktop OTDR has several features not found in more portable, battery-powered, handheld devices. Both types are efficient and accurate fiber break locators and provide other information as well. The latest handheld OTDRs are suitable for field data collection. In addition to fiber breaks, they measure and locate points of high loss or reflectance, end-to-end loss, and optical return loss. The data can be stored and then downloaded to a PC with the appropriate software installed for further analysis or emailing to a colleague.

Test unshielded Cat 5e twisted pairs and Ethernet connections (4)

A time domain reflectometer, available in both desktop and portable models, can be optimized for evaluating copper data links over UTP or coaxial cable. Again, a pulse, now electrical instead of light, is injected into one end of the compound under study, and all reflections are timed and analyzed at the same end. If the cable has a consistent and correct characteristic impedance and is properly terminated, there will be no reflections, indicating a good connection. Without reflections it is impossible to determine the length of the cable. However, the sensitivity of the instrument is so high that even with a near-perfect cable, there will be a slight deviation that will produce a small harmless reflection that can be used to measure length.

(Video) What Ethernet Cable to Use? Cat5? Cat6? Cat7?

If the cable is shorted at the opposite end, the transmitted pulse will not be absorbed as it would be if the impedance of the cable matched the impedance of the load. Consequently, the voltage at the source drops to zero. By measuring the time interval, the distance to the short can be determined.

If there is an open circuit at the opposite end (infinite impedance), the retrace pulse increases the source voltage because it has the same polarity and the time interval indicates the fault location.

TDR analysis has many different applications beyond evaluating data links and locating faults. An example is the detection and location of illegal wiretapping that creates discontinuities that lead to reflections. Another example is the non-destructive mapping of rebars in large concrete structures such as dams. Another example is finding an electrical fault in the hidden wiring of a large aircraft. In addition, time-domain reflectometry is used to inspect printed circuit boards to reveal hard-to-detect soldering defects due to open circuits.

(Video) T568A vs T568B - what's the difference and how to test patch leads.

Test unshielded Cat 5e twisted pairs and Ethernet connections (5)TDRs are quite expensive, and unless you take these measurements professionally and regularly, you may not be able to justify the cost. But if you're reading this, you probably have an oscilloscope and a signal generator.

The context and the math are quite complex. (The advantage of a factory built time domain reflectometer is that it is easy to use and will do the calculations for you and display the results in a way that is easy to communicate.) There are many plans and discussions on the internet. The best explanation I've ever seen, you can seeHere.

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