Network test equipment is the handheld and lab instruments that engineers use to measure fibre cables, radio signals and network equipment, usually before a link goes live and again when it fails. It is also called network test and measurement equipment. Its main buyers are telecom operators, the companies that build networks for them, and the makers of network equipment.
There are three main kinds. Fibre testers check optical fibre, the glass cable that carries data as pulses of light. The best known is the OTDR, or optical time-domain reflectometer. It sends short pulses of light into the fibre and measures the small amount of light that comes back from each point along it. From the timing of the returning light, it shows exactly where a joint is weak, or where the fibre is bent or broken. Radio testers check mobile signals: how strong the signal from a new site is, whether it disturbs other sites, and how fast data moves. Engineers often carry these in a car around the area, in what is called a drive test. Lab testers create heavy traffic, to check that a router or a 5G core can handle the load it is designed for, before it is installed.
Take, for example, a telecom operator laying new fibre between Jaipur and Ajmer, a distance of about 135 km, to connect new 5G sites. The cable is laid in sections. The sections are joined by splicing, which means melting two fibre ends together. A good splice loses almost no light, less than 0.1 dB. Before the link goes live, a technician connects an OTDR at the Jaipur end. Its trace shows a clean line, except for one event at 42.6 km: a loss of 1.4 dB. The crew digs at that point and finds a splice that was made badly in the rain. They redo it and test again, and the event is gone. The OTDR report is saved. If the link fails next year, the new trace will be compared with this one.
The same work happens at each radio site. Before a new site carries customers, engineers measure the signal from its radio units and antennas across the area it should cover, and check the download speed customers would get there.
Test equipment also checks optical transport equipment, which sends many signals over one fibre, each on a different colour of light. Many instruments now send their results to central software. Operators then use these results in telecom service assurance, to compare the live network with how it performed when it was new.
How is it different from oscilloscopes and other electronic test instruments? Those measure electronic circuits on a lab bench, such as the signals inside a circuit board. Network test equipment measures links and networks, often out in the field. Some of the same companies make both.