A gateway allows network based on completely different protocols communicate with each other.
To this end, a Gateway from a protocol implementation. The gateway is allowed means all that is necessary for conversion of data, including the omission of information where the destination network can not be transported. In detail, all log information to be appended to a data package (for example, IPX / SPX), removed, and by others (for example, the Internet protocol family) are replaced. There are also gateways to many other uses, such as SMS gateways (e-mail, etc., etc. Short Message Service), fax to e-mail, e-mail to Speech
Deferred to the router 
Gateways are in the current language is often equated with routers, although router only work on the third layer (network layer) of the OSI reference model, a gateway on the other hand, four to seven layers can be implemented. Often, the (acting, especially in small networks as a gateway) router as a default gateway is called.
Gateways do not work well packed with so-called tunneling protocols, where one protocol to another, transported to the destination network and there will be unpacked (eg NetBIOS over TCP / IP). Set a record in real terms in another, there is no need for the main protocol used in the target network.
Some called for a combination device in the home router and DSL modem as your Internet gateway. These devices combine, in simple terms, the function of networks to interconnect (routing), with the ability to use different protocols for this (Gateway). Thus, IP packets from the home network with DSL use mostly through the PPPoE protocol in the network of the provider notified.
The log name is called a default gateway while at the implementation level as layers because, in contrast to the simple router the ability of an independent, temporarily independent of any main system operation can result. This refers not only to WAN activities, but also to all processes on operating systems which are possible today.