What device is required to attach a non-ISDN device to an ISDN network?

A terminal adaptor (TA) is essential for connecting non-ISDN devices to an ISDN network because it effectively translates the communication protocols and formats used by standard devices into those compatible with ISDN. ISDN (Integrated Services Digital Network) operates on a specific digital communication standard that many traditional devices do not support. The TA serves as an interface that allows these devices, which might otherwise operate on analog signals or different communication protocols, to access the ISDN network for data transmission.

In terms of connectivity, a TA can handle incoming and outgoing data from the non-ISDN device, converting it as necessary to make it viable for ISDN standards. This is particularly important for ensuring seamless communication across diverse network types.

Other devices, like a router, modem, or switch, serve different purposes within a network. Routers typically direct traffic between different networks, modems convert digital signals to analog for transmission over phone lines, and switches connect devices within a local area network. None of these devices provide the specific functionality required to directly bridge the gap between non-ISDN and ISDN systems, which is why a terminal adaptor is the correct choice for this application.