In a communications network, a gateway is a network node equipped for interfacing with another network that uses different protocols. Broadly speaking a gateway is simply an entrance point for one network to another network, hence the name gateway.
A gateway may contain devices such as protocol translators, impedance matching devices, rate converters, fault isolators, or signal translators as necessary to provide system interoperability. It also requires the establishment of mutually acceptable administrative procedures between both networks.
A protocol translation/mapping gateway interconnects networks with different network protocol technologies by performing the required protocol conversions.