ATU-R（ADSL Tranceiver Unit Remote），又称非对称数字用户回路远程终止单元，是ADSL线路当中，放在用户端的设备，用以连接宽带上网，为「ADSL调制解调器」的正式名称，俗称“小乌龟”。

目前**使用的ATU-R，除了内置ADSL调制解调器功能，也具备部份路由器的功能，可以是外置式或内置插卡式。而ATU-R的主要工作，是与局端的ATU-C（ADSL Transceiver Unit Central）作搭配，因此不同区域，因为局端的ATU-C设备不一样，很有可能所用的ATU-R也不相同。

A digital subscriber line (DSL) modem is a device used to connect a computer or router to a telephone line which provides the digital subscriber line service for connectivity to the Internet, which is often called DSL broadband.

The term DSL modem is technically used to describe a modem which connects to a single computer, through an Ethernet Port, USB port, or is installed in a computer PCI slot. The more common DSL router is a standalone device that combines the function of a DSL modem and a router, and can connect multiple computers through multiple Ethernet ports or an integral wireless access point. Also called a residential gateway, a DSL router usually manages the connection and sharing of the DSL service in a home or small office network.