GarrettCom OSI manual Gateways

•Integration: The ability to manage a large network from central or distributed locations, economies of scale, network visibility, and other factors without time-consuming testing of incompatible interfaces can provide huge benefits.

•VLAN support: The ability to define virtual networks for managing traffic and security.

GATEWAYS

Gateways make communications possible between dissimilar systems. The range and types of gateway devices are broad, and the configuration and proper matching of two different interfaces can be a daunting task. The difficulty is based on how many layers of the two architectures must be matched and integrated. The ideal is to make the gateway transparent to both systems. System A thinks it is just talking to another member of its network and is not aware that system B is different.

When a gateway only has to deal with the routing, addressing, and transmission of data, the configuration is relatively simple. Referring back to the OSI model, this covers layers one to three. When it involves applications and message syntax, things get a lot stickier, and more time consuming. Also, the more layers that must be converted, the more processing overhead is involved. This can be unfortunate for critical real-time systems.

When the conversion involves the interconnection of systems and the transport of data, several Ethernet vendors offer components to efficiently handle that task.

•Media converters operate at the physical layer, match the signal transmission and media connecter differences. The data itself is transparent. Many Ethernet hubs and switches provide plug-in modules to simplify integration.

•Bridge devices generally operate at the data link layer (L2) and check L2 addresses, limiting unnecessary traffic. These can also be plug-in modules. Other so-called bridges operate more like routers and offer protocol conversion as well.

•Routers are layer three devices. Some provide protocol conversion using plug-in cards to handle token bus, token ring, and Ethernet protocols among others. A router checks L2 and L3 addresses and makes routing decisions based on its configuration. Others may offer support for proprietary protocols or a programming language to “roll your own” changes.

The amount of effort this takes, of course, is based on how dissimilar the systems are and how much control of the subnets is required. On the other hand, when everything is Ethernet-based and uses TCP/IP to support applications, the time, effort, and problems encountered are exponentially less.

Distributed with permission of author by ISA 2006

Presented at ISA EXPO 2006