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Integrated Services Digital Network adapters can be used to send voice, data, audio, or video over standard telephone cabling. ISDN adapters must be connected directly to a digital telephone network. ISDN adapters are not actually modems, since they neither modulate nor demodulate the digital ISDN signal.

Like standard modems, ISDN adapters are available both as internal devices that connect directly to a computer's expansion bus and as external devices that connect to one of a computer's serial or parallel ports. ISDN can provide data throughput rates from 56 Kbps to 1.544 Mbps (using a T1 carrier service).

ISDN hardware requires a NT (network termination) device, which converts network data signals into the signaling protocols used by ISDN. Some times, the NT interface is included, or integrated, with ISDN adapters and ISDN-compatible routers. In other cases, an NT device separate from the adapter or router must be implemented.

ISDN works at the physical, data link, network, and transport layers of the OSI Model.

Network Interface Card, or NIC is a hardware card installed in a computer so it can communicate on a network. The network adapter provides one or more ports for the network cable to connect to, and it transmits and receives data onto the network cable.Every networked computer must also have a network adapter driver, which controls the network adapter. Each network adapter driver is configured to run with a certain type of network adapter.

A networked computer must also have one or more protocol drivers (sometimes called a transport protocol or just a protocol). The protocol driver works between the upper-level network software and the network adapter to package data to be sent on the network.

In most cases, for two computers to communicate on a network, they must use identical protocols. Sometimes, a computer is configured to use multiple protocols. In this case, two computers need only one protocol in common to communicate. For example, a computer running File and Printer Sharing for Microsoft Networks that uses both NetBEUI and TCP/IP can communicate with computers using only NetBEUI or TCP/IP.

A CSU/DSU is a device that combines the functionality of a channel service unit (CSU) and a data service unit (DSU). These devices are used to connect a LAN to a WAN, and they take care of all the translation required to convert a data stream between these two methods of communication.

A DSU provides all the handshaking and error correction required to maintain a connection across a wide area link, similar to a modem. The DSU will accept a serial data stream from a device on the LAN and translate this into a useable data stream for the digital WAN network. It will also take care of converting any inbound data streams from the WAN back to a serial communication.

A CSU is similar to a DSU except it does not have the ability to provide handshaking or error correction. It is strictly an interface between the LAN and the WAN and relies on some other device to provide handshaking and error correction.