Chapter 15 / 15.2 / 15.2.4

15.2.4 Higher-Layer Interworking

Some communication systems require more than simple packet forwarding. Networks using different protocols, addressing schemes, or application formats may require translation between incompatible systems.

These functions are performed by gateways, which operate at the upper layers of the protocol architecture. Unlike routers, which forward packets while preserving their contents, gateways may modify message formats, convert protocols, or translate application data.

Examples include:

• email gateways that transfer messages between different messaging systems;
• Voice over IP (VoIP) gateways connecting IP networks to the traditional telephone network; and
• protocol converters that allow legacy industrial equipment to communicate with modern IP-based networks.

Because gateways understand the application or transport protocols being exchanged, they operate at a higher level than routers and provide interoperability between otherwise incompatible systems.