How a cell phone works

[tags]Chris Pirillo, Lockergnome, Gnomedex, Cell, Phones, Mobile, Devices[/tags]

Today, according to some researchers, there are enough cell phones in the USA to give 2 to every man, woman and child. That’s allot of mobile devices. But how do they work? It all has to do with things called HLR, VLR, and MSC. Each of these stand for a particular part of the cell phone system and each work together to complete a call from one phone to another.

1. HLR: Home Location Register

This is the main database and holds all your information, including your address, account status, and options such as whether or not you have text messaging, internet, etc.

2. VLR: Visiting Location Register

This keeps temporary information such as your current location. You might think of this as RAM that is in a computer. It manages requests from subscribers that are out of thier home area or pulling from another service provider’s tower.

3. MSC: Master Switching Center

This is where all the requests are collected, approved (or denied) and sent to the proper areas.

Let’s say that you are on vacation and not in your home area when you initiate a call. here’s what happens when you press the “send” key.

The VLR sends out a request to the MSC for access to the network and permission to make the call. The MSC then queries the HLR to see if your account is active, if you have permission to make calls from out of your area, how many minutes you have left, etc. The HLR then gives the all clear to the MSC to process the call and the MSC then gives the VLR the proper signals to access and use the network.

This is a very simplified explanation of the system, but anything that goes wrong within any one of these systems will cause the call to fail. There are other systems and “switches” that are involved but these three are the main ones that allow you to make and receive calls. I will go into these in another post.

Have questions about cell phones and how they work? Give me an email at  teddc at bellsouth.net and I’ll do my best to answer them.

Cell Phone Tip of the Post:

If you need to find your IMEI number just press *#06# on most mobile phones. It should show up on the screen.