gateway

A term used to describe a variety of networking technologies that
enable communication between different networking architectures and
protocols.

Overview

Gateways generally operate at the higher levels of the Open Systems
Interconnection (OSI) reference model for networking. They are
commonly used to provide connectivity between two different protocol
stacks that might be running on different systems. Examples include
the following:

. E-mail gateways.for example, a gateway that receives Simple Mail
Transfer Protocol (SMTP) e-mail, translates it into a standard X.400
format, and forwards it to its destination

. Gateway Service for NetWare (GSNW), which enables a machine running
Microsoft Windows NT Server, or Windows 2000 Server to be a gateway
for Windows clients so that they can access file and print resources
on a NetWare server

. Gateways between a Systems Network Architecture (SNA) host and
computers on a Transmission Control Protocol/Internet Protocol
(TCP/IP) network, such as the one provided by Microsoft SNA Server

. A packet assembler/disassembler (PAD) that provides connectivity
between a local area network (LAN) and an X.25 packet-switching
network

A gateway is usually a dedicated device or a set of services running
on a dedicated computer. Gateways are essentially devices that direct
network traffic in some fashion and translate that information.