Wiring standards and system tests

The network cabling system is the foundation of the network. Its health is crucial to network users. There are several important metrics for measuring the health of the wiring system, including near-end crosstalk NEXT), attenuation, length, wiring diagram, characteristic impedance and noise. Now, Category 5 twisted pair wires are becoming more and more popular, and have become the preferred cabling system for high-speed LAN. Class 5 UTP installation of International has long been standard to follow, that is, EIA/TIA 568A TSB-67. We will further discuss this new cable connection Standard below. We will also discuss some questions that users should know when testing the connection characteristics of Category 5 twisted pair wires.

Network and power supply standards

There are usually two types of standards used for cable installation testing, namely network standards and cable standards. If you are clear about which network environment the selected cabling system will be used, the corresponding IEEE network standard can be used to verify whether the cabling system supports applications in this particular network environment. The network standard defines the end-to-end connection specifications for the cable medium used in the network. Network standards are especially useful when you need to know whether a network fault is caused by a cable. Currently, most common networks run at 10 Mbps. 650 or 652 of existing low-price cable testers, such as Fluke, is used to test whether these cables comply with network standards. These cable testers provide automated testing capabilities that allow them to automatically test a variety of cable metrics and compare them with the metrics in the selected Standard. The test results will be given by the tester within the standard range.

Sometimes cabling construction engineers or users may not be able to determine at the beginning what network signal types the cabling system will be used to support. For example, when a contractor starts construction of a smart building, they do not know what kind of signals will be transmitted using these cables in the future. Further, users may upgrade the network or change the network type in the future. In order to reduce the cost of upgrade, users hope to make full use of their cabling systems. Therefore, it is very important to check whether the cabling system can support future network applications within a period of time. Most current networks, such as Ethernet and ring-based network, use UTP cables. Five types of UTP can also be used to support some new network platforms, such as 155 m atm, 100Base-TX, and 100Base-VG. Considering its relatively low price, five types of UTP are becoming the most widely used cable system.

As almost all high-speed networks support category 5 twisted pair wires, You need to determine whether their cabling systems meet the five UTP installation specifications. To meet user needs, TIA Communications Industry Association) has developed the EIA/TIA 568A TSB-67 standard, which is applicable to the already installed twisted pair connection network. It provides users with an acceptance specification for "Certification" Whether the cabling system of twisted pair wires meets the standards of Category 5 cables.

TSB-67 EIA/TIA 568A

1. Overview of TSB-67 content

The TSB-67 Board consists of cable manufacturers, network hardware manufacturers, and cable tester manufacturers. The purpose of the TSB-67 is to provide a standard for users and constructors of the 100AWG twisted pair to verify the specification and accuracy of the testing instrument so that they can truly complete the task of verifying the quality of the cable. TSB-67 includes:

Definition of two "connection" models

Define the transmission parameters to be tested

Define each connection model and three, four, and five links

PASS/FALL test limits

Reduce test report items

Define the performance requirements of the field tester and verify whether the system meets these requirements

Comparison of field tester and laboratory equipment testing results

2. Connection level defined in TSB-67

The connection levels defined in the TSB-67 have 3 connector 3 categories, 4 categories, and 5 categories. Table 1 lists the application of these connection levels. The LAN types supported by these categories are not mentioned in the TSB-67 ).

3. "join" model defined in TSB-67

The standard defines two Connection Models: primary Channel and Basic Link ). The Channel defines the standard requirements for end-to-end transmission with user end cables. It is important to thoroughly understand and distinguish the different features of the Channel and Basic Link models.

The same principle for all connection models is that the connector that matches the instrument is defined as part of the instrument, not included in the connection. The reason for this definition is that the cable connection part includes Plug and socket) the transmission performance is defined according to the pair cannot be separated.

Defining the end cables separately is in progress. Because the device's socket and its connection part are obviously part of the device, the matching plug is part of the device, although physically speaking, the plug is not part of the device and will always be connected to the cable line ). This definition method allows the manufacturers of field testers to face interesting challenges. The transmission parameters of the "connection" must be measured at the outlet of the instrument and the corresponding plug of the end cable, but at the same time, we must try to suppress the impact of the instrument's socket and connected plug on the measurement results in some way, otherwise there will be additional errors during testing.

4. Channel) Model Definition

It represents an end-to-end connection. One of the most easily remembered features of the Channel model is that each end of the Channel must have two connection points, excluding the connection points of the device ). The user's end cable is included in the connection, so the Test Instrument and the socket of the remote unit must match the user's end cable connector, in order to form the test conditions for the Channel. The vast majority of these matching plug are RJ-45 plug.

The transfer point Transition ctor in the connection) is an optional part and is not used in most cases. It is usually used in future modular office systems. The crossover cables in the distribution cabinet are usually not drawn, but replaced by socket panel jumpers. Therefore, such a Channel only has a transmission contact at each end. Because the preparation is different, the test limits are different. The user's end cable is always used no matter whether there is a transfer point.

5. Basic Link Basic connection) Model Definition

This model describes the testing requirements for contractors responsible for installation of fixed cables only in buildings. The easy-to-remember feature of the Basic Link model is that there is only one connection point at each end of the connection, not the connection point to the tester ). Compared with channels, Basic Link has more stringent test requirements, because when connecting network devices or workstation together, designers should consider setting aside performance margins for users' end cables.

In Basic Link mode, the end cable must be connected to the tester and the End Socket. There is no requirement that the plug must be RJ-45-type. In fact, many instruments usually do not use RJ-45 connectors to avoid the various limitations it brings. Common testing instruments use special low-NEXT value dedicated cable connectors to meet TSB-67 Requirements for the best performance (Advanced accuracy)

TSB-67 test parameters

1. Wiring Diagram

It verifies the correct line-to-line connection. The wiring diagram must comply with EIA 568A or 568B definitions. From the perspective of signal science, there is no essential difference between the two standards. The only difference is that the colors of line pairs are different.

It is not enough to test the DC resistance only. You also need to use an AC signal to test whether the cable has a string wound Split Pairs ). Other errors, such as open circuit and short circuit, can be detected by Pulse Reflection.

2. Length

The physical length of the connection. After the maximum error of the NVP value specified by the cable manufacturer and the error caused by the TDR technology used for length measurement are included, the error limit of the measurement length is:

Channel: 100 m + 15% × 115 m = m

Basic Link: 94 m + 15% × 94m = 108.1 m

3. Attenuation

Test limits at specific frequencies are listed in table 2. The TSB-67 requires testing at least once every 1MHz interval within the measured frequency band.

4. Near-end crosstalk NEXT

There are two important rules for NEXT testing.

A. the test of the NEXT value must be bidirectional, which is explicitly stated in the TSB-67 specification because the test results at one end of the NEXT value may be passed, the other end may fail.

B. Frequency Resolution

Lists the relationship between the NEXT value and frequency of typical five types of cables.

The relationship between the NEXT value and frequency of the five twisted pair wires shows that the NEXT value is non-linear, and there are many peaks and troughs at different frequencies. To accurately measure the nearest boundary, the test frequency step must meet the requirements shown in table 3.

Tester Performance Requirements

The definition of performance requirements for field Cable Testing Instruments seems unusual. Two performance testing level-1 and level-2 instruments have been defined.

The level-1 precision field tester has a much larger error than the level-2 precision field tester. Therefore, it is generally recommended that the level-2 precision tester be used for the certification test of the wiring system. However, if the connection performance of the tested cable is very good and the measured parameters are far away from the limit value, the first-level precision tester does not report results close to the accuracy ability of the instrument, then the test result is credible.

Summary

The new EIA/TIA 568A TSB-67 specification can be used to verify that installed twisted pair cabling systems meet specific levels of requirements. According to the definition and guidance of TSB-67, users can trust that the cable can support their various network applications today and in the future. The user can also choose a cable Tester that can precisely authenticate twisted pair wires to meet the various test conditions for field cable testing required by the TSB-67.