Network test instruments are divided into two basic categories: Physical Layer Analyzers and Higher Protocol Layer Analyzers. These categories are linked to the OSI Reference Model. Higher protocol layer analyzers can perform test and measurement across six layers of the OSI model; whereas, physical layer analyzers focus on one layer.

Physical Layer Analyzers: On the physical layer (OSI Layer 1), the instruments used to measure electrical and electronic characteristics include multimeters, cable testers, optical time domain reflectometers (OTDRs), oscilloscopes, signal level meters, and spectrum analyzers. The most important parameters measured by these instruments are line characteristics such as cable length, resistance, attenuation, crosstalk, reflections caused by connectors and terminating resistors, and electromagnetic interference from external sources.

Higher Protocol Layer Analyzers: On the higher protocol layer (OSI Layer 2-7), processes are monitored and analyzed using protocol analyzers. These instruments examine frames, packets, data transfer integrity, session connections, data transformations, and application performance. There are a variety of protocol analyzers such as universal devices with special modules for different tasks, small hand-held devices, and software packages installed in high-performance network node.

Application performance is measured using software agents that simulate network use by typical applications to determine throughput and other characteristics.