What is a Gateway?
A gateway interconnecting networks above the network layer is the most complex network interconnection device. It is used only for interconnection of different networks between two high-level protocols. The Gateways can be used for both WAN and LAN interconnects.
A gateway is a computer system or device that serves as a transitional task. The gateway is a translator between two systems that use different communication protocols, data formats or languages, or even completely different architectures. Unlike the bridges, which simply convey information, the Gateways repackage the information they receive to suit the needs of the destination system.
How does the Gateway work?
We can take an example.
There is a boy, named Tom (Data). Tom lives in one room of an apartment. There are many friends in other rooms. Tom’s parents are the Gateway. If Tom want to play with one friend, he needs to shout friend’s name in the room. If his friend hears that, he will come and play with Tom.
Tom’s parents (Gateway) don’t allow Tom go out of the room. Whatever Tom want to do, he need his parents’ help. For example. Tom wants to chat with Peter, but Peter lives at another apartment. Tom can’t shout Peter’s name and doesn’t know the telephone number of Peter. However, there is a telephone number list of all the classmates, at Tom’s teacher’s home. Then, Tom’s teacher is the DNS Server. So, there will be this dialogue:
Tom: Mom, I want to ask my teacher for Peter’s telephone number.
Mom: Ok. (Mom phoned the teacher and got the number.) Well, Peter’s telephone number is 211.99.99.99.
Tom: Great! Mom, I want to chat with Peter. Can you help me?
Mom: Ok (Mom sent a request to the telephone office. Peter’s parents (Gateway) got the request and they told the request to Peter.)
At last, Tom can chat with Peter now.
Figure1. How the Gateway work.
Types of Gateway
There are two main types of gateways.
1. Transmission
With Transmission Gateways, hosts across different networks can establish cascaded, point-to-point transport connections across multiple networks. For example, the commonly used router is the transmission gateway. The function of the "gateway" is to connect two different network segments, or to connect two different routing protocols, such as RIP, EIGRP, OSPF, BGP, and so on.
2. Application
The Application Gateway is in the application layer protocol conversion. For example, there is one host is running the ISO e-mail standard and the other host is using the Internet e-mail standard. If both hosts need to exchange e-mail, they must go through an e-mail gateway for protocol translation. The e-mail gateway is an application gateway.