In telecommunications, the term gateway has the following meanings:
- In a communications network, a network node equipped for interfacing with another network that uses different protocols.
- 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 the two networks.
- A protocol translation/mapping gateway interconnects networks with different network protocol technologies by performing the required protocol conversions.
- Loosely, a computer configured to perform the tasks of a gateway. For a specific case, see default gateway.
Routers exemplify special cases of gateways.
Gateways, also called protocol converters, can operate at any layer of the OSI model. The job of a gateway is much more complex than that of a router or switch. Typically, a gateway must convert one protocol stack into another.
- A gateway may connect an AppleTalk network to nodes on a DECnet network
- A very popular example is connecting a Local Area Network or Wireless LAN to the Internet or other Wide Area Network. In this case the gateway connects an IPX/SPX (the LAN) to a TCP/IP network (the Internet).
Gateways that connect two IP-based networks, like TCP/IP with IPX/SPX, have two IP addresses, one on each network. An address like 192.168.1.xxx is a Local Area Network address, and is the address to which traffic is sent from the LAN. The other IP address is the Wide Area Network address, this is the address to which traffic is sent coming from the WAN. When this is the Internet, that address is usually assigned by an ISP.
When talking about the gateway IP address, commonly the LAN-address of the gateway is meant.
The addresses of computers connected to the LAN are hidden behind the gateway. That is, the WAN can only see the gateway's IP address. To regulate traffic between the WAN and the LAN, the gateway commonly performs Network Address Translation (NAT), presenting all of the LAN traffic to the WAN as coming from the gateway's WAN IP address and doing packet sorting and distribution of return WAN traffic to the local network.