ISDN testers verify the communication services provided by ISDN equipment

Network test equipment is used to test, probe, and analyze telecommunication, network and telephone systems

Network modems (modulators-demodulators) are devices or programs that allow computers to transmit data over telephone lines.

Bit error rate testers are devices or procedures that measure the bit error rate (BER) for a specific transmission.

Patch panels are groups of ports used to connect lines between communications and electronic devices.

Network analyzers and protocol analyzers are test equipment used to troubleshoot and analyze network problems

Network switches route packets between ports at the OSI layer 2, which means that (in Ethernet) the switches decide where incoming packets are transferred to, based on the NIC's 48-bit address.