Embedded Systems: Programmable Logic -> Common gateway networks enable remote programs

Gateway modem
In this scenario a gateway network communicates through a pair of modems to the remote device using a lightweight protocol. This scenario contains all of the advantages of the "lightweight network-modem" scenario as well as all of the advantages of a general gateway network. In addition, the local client, the gateway and the remote device can be in three different locations, or the local client and gateway can be in the same location and the remote device in another location. Some Internet service providers, such as AT&T Global Network Services, can provide device gateway services and local phone connections to just about anywhere in the world.

RS485 subnet
To utilize an RS485 subnet with a gateway network, the gateway is the remote RS485 subnet master that communicates to the subnet devices. This is a good arrangement if a ga teway and several devices are within the range of an RS485 subnet.

Modem-to-RS485 subnet
This network arrangement is a combination of the modem and RS485 subnet gateway networks described.

Instead of a gateway linking over a pair of modems to a remote device, the gateway links over a pair of modems to an RS485 subnet master, which communicates to the subnet devices.

Only one modem is needed for the entire subnet of devices. The gateway does not need to be in the same location as the RS485 subnet, since it communicates with the subnet via modem. The same gateway could, in fact, access multiple remote RS485 subnets. Again, an ISP could manage the gateway and phone network.

Ethernet subnet
In this scenario a gateway network communicates on an Ethernet subnet with remote devices, using a lightweight protocol. This arrangement is similar to the RS485 subnet example but using Ethernet as the transport medium instead of an RS485 subnet. This t ype of network architecture leverages existing Ethernet wiring.

Other options
In addition, other gateway network subnet technologies exist. They include power line, RF, IR, two-way pager, field bus and TCP/IP.