A random-access channel (RACH) is a communication mechanism used by mobile phones and other wireless devices on a TDMA-based network. The RACH is used to get the attention of a base station in order to initially synchronize the device's transmission with the base station. It is a shared channel that is used by wireless access terminals to access the access network (TDMA/FDMA, and CDMA based network) especially for initial access and bursty data transmission. RACH is transport-layer channel; the corresponding physical-layer channel is PRACH.
A random-access channel like that of mobile phone networks is also used in the OpenAirMesh network, between cluster heads and mesh routers.
A key feature of a random-access channel is that messages are not scheduled (compared to, for example, a "dedicated channel" in UMTS, which is assigned exclusively to one user at a time). There is no certainty that only a single device makes a connection attempt at one time, so collisions can result.
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—Cardinal John Henry Newman (1801–1890)