Judging by the number of emails we receive asking how to do it, lots of people are trying – and failing – to get their Xbox 360 games console online via a 3G modem. It should be straightforward, but it seems that Xbox Live doesn’t always work as expected over a mobile broadband connection – which is a problem if that’s the only internet connection you have access to.

The good news is that it is relatively straightforward to get an Xbox 360 online using a 3G USB modem. The bad news is that it’s not just a case of plugging a modem directly into the Xbox 360’s USB port – there are no suitable drivers, and no way to install them even if there were. But there is a one way to do it.

If you have a Windows PC, you can connect the Xbox 360 to it with an Ethernet cable and then plug the modem into the PC. Windows Internet Connection Sharing then lets you share the mobile broadband connection with the Xbox 360 – and Xbox Live will work in the usual way. Well, sort of.

NAT matters

The catch is that mobile broadband providers use subtly different settings for their services and the important one is NAT – Network Address Translation. Among other things, NAT governs the ports that are available over your internet connection – essentially holes in the mobile broadband provider’s firewall through which data can pass unimpeded.

Ideally, you should be able to use any port you like, but some providers place tight controls on their mobile broadband NAT, usually for security reasons. When Xbox Live tests an internet connection, it identifies three types of NAT – Open, Moderate and Strict.

The type of NAT deployed by your mobile broadband provider will affect your ability to host and join Xbox Live games, as this table shows:

An Open NAT is obviously the most desirable configuration, but a Strict NAT doesn’t rule out Xbox Live completely – it just means that you won’t be able to play with other people with a Strict NAT, or host games that people with Moderate or Strict NAT settings can join.

Unfortunately, the NAT settings for mobile broadband services are controlled by the provider and there’s no getting around a service with a NAT set to Strict. You can read more about the different types of NAT at the Xbox Live support site.

Vodafone and 3 both use an Open NAT; O2 is Strict – these are the results of the Xbox Live connection tests we ran with each modem. We weren't able to test modems from Orange and T-Mobile, but Orange did confirm that it doesn't block any ports, which means Xbox Live should detect an Open NAT with its mobile broadband service. We're still waiting to hear from T-Mobile though, and we'll post an update as soon as it replies.

Game on..?

Three final points. First, online gaming (particularly first-person shooters) is heavily reliant on a low ping. Too high a ping (measured in milliseconds) and the game will ‘lag’ – there will be a delay in your actions and what you see on-screen.

Our tests of mobile broadband modems show ping scores around the 150ms mark – not the best, but still fine for online gaming. If you think an online game is lagging, you can test your broadband modem’s ping by opening a command prompt window on the PC (Start > Run > cmd) and typing ping www.google.com (or a popular website of your choice) , then pressing Enter. The value after time= is your ping.

Second, online gaming with Xbox Live downloads more data than you might think. In addition to game updates, data is also downloaded as you play – we measured 82Mb after one hour of playing Team Fortress 2. This can be an issue if your tariff has a stingy data allowance and/or high excess use charges, so examine the different mobile broadband deals carefully if you're looking for one just for gaming.

Third, check the T&Cs of the mobile broadband provider you plan to use before signing up to a contract. Some providers explicitly prohibit the use of their mobile broadband service on a local network – and that’s just what Internet Connection Sharing is doing. That said, short of monitoring your internet traffic, there’s no easy way for a provider to detect that you’ve connected a games console to their service, so it shouldn’t be a problem. 

So, with that out of the way, let's get started...