Which type of network medium is used by an Integrated Services Digital Network (ISDN) adapter?

An Integrated Services Digital Network (ISDN) adapter primarily utilizes copper telephone wire as its network medium. ISDN is designed to carry voice, video, and data over traditional copper telephone lines, allowing for digital transmission rather than the analog signals typically found in standard telephone service. This digital capability enhances call quality and allows for higher data transfer rates compared to traditional phone lines.

The use of copper telephone wire is fundamental to ISDN's operation, enabling it to establish a digital connection by using existing infrastructures such as twisted-pair copper cables. Other mediums, like fiber optic cable or coaxial cable, are not part of the ISDN framework. Fiber optic, while offering much higher speeds and longer distances, is not used in ISDN. Coaxial cable is typically used for cable internet and television services, rather than for telephone networks. Wireless signals, while increasingly common in modern networking, are not applicable in the context of traditional ISDN connections, which rely on wired infrastructure.