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Modems, Routers, Gateways: What’s the Difference?

The different devices and functionality of industrial cellular hardware can be confusing. Sales Engineering Manager, Randall Kerr, clears up the confusion and simple defines the differences between modems, routers, and gateways.

It is important to clearly understand the device functionality of modems, routers, and gateways when selecting cellular communication hardware. The differences between these devices are often confused with one another, which is not ideal for industrial cellular applications. Engineering Manager, Randall Kerr, defines and simplifies the differences between these pieces of cellular equipment in this short video: 
Dec 12, 2017
3:18
Show Transcript

People sometimes confuse the functionality of cellular modems with that of routers or gateways. So let's see if I can provide a little distinction and clarity around the subject. When we talk about cellular communications hardware, the first piece of equipment to address is the modem. The key thing to understand is that a modem has historically been a dumb device, not intelligent and not programmable. A modem simply sends traffic from point A to point B without further manipulation, as such, it's not going to provide much data protection, and it probably won't have a firewall. The modem will just do as it's told without asking questions.

A router, on the other hand, is a highly intelligent device. Every Digi router actually contains a cellular modem. The highest grade routers can even support multiple cellular carriers. So if you're running traffic on one carrier's network and for some reason, that connection goes down, these routers are able to offer failover to a secondary cellular connection. A quality router is going to provide a robust firewall so that it can handle packet-level traffic inspection, reconciling incoming traffic with outgoing requests. It should also support numerous types of tunnel options for data security.

IPSec is a very popular tunnel for encrypted traffic, but other options include GRE, L2TP, PPTP, and even open VPN. Many industrial-grade cellular routers will actually contain an input/output or I/O option. This enables users to handle tasks like field device control and operations management. Let's say you're monitoring the temperature of a particular asset that has been deployed in the field, perhaps it's a pump, and the temperature goes too high. Using the onboard I/O, you can issue a shutdown order to avoid damaging the pump. Finally, many routers contain onboard programming languages and execution models, so if you want to avoid deploying additional hardware in the field, this is another element to consider.

The last device type is the cellular gateway. Gateways don't possess the degree of networking traffic control that routers do, but they usually offer simplified configuration. Gateways often tend to have some kind of an onboard programming model as well, and some even offer I/O options. The important thing about gateways is that by definition they provide protocol translation. So it might be Zigbee, wired hard, or Modbus to cellular, or even other technologies. There are numerous options where cellular gateways are concerned.

So those are the differences between modems, routers, and gateways. I hope that helps provide some clarification and better understanding about their features and uses. For more informational videos, go to digi.com.

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