The word gateway is a general term that refers to a node on a network that acts as an entrance to another network and often serves to translate between different communications protocols, data formats, etc.
Gateways are customized and designed to perform specific functions and are used on a case-by-case basis. A gateway can operate at any of the seven layers of the OSI (open systems interconnect) model, depending on the type of services that it is providing.
An Internet gateway is a device that is used to connect an enterprise or other organization to the Internet. In addition to merely providing a connection, it typically also provides other functions as well, including serving as both a router (which directs individual packets to their next node) and a firewall (which filters out inappropriate packets).
Other common uses of gateways include a file translator (e.g., allowing Macintoshes to access files on a Linux server), a mail translator (i.e., between two types of mail protocols), a network protocol translator (e.g., converting between between TCP/IP and AppleTalk) and an interface between VoIP (voice over Internet protocol) and the PSTN (public switched telephone network).
The ability of gateways to translate between very different protocols and formats comes at a cost; it is the slowing down of the flow of data as compared with what would occur in the absence of a gateway. Likewise, there is a cost to the great diversity and flexibility of gateways; it is that they are usually more difficult to install and configure than other network devices.
Created November 20, 2005.