Cell-phone codes – how cell phones work _ howstuffworks

• When you first power up the phone, it listens for an SID (see sidebar) on the control channel. Msci world index zusammensetzung The control channel is a special frequency that the phone and base station use to talk to one another about things like call set-up and channel changing. Msci world value index If the phone cannot find any control channels to listen to, it knows it is out of range and displays a “no service” message.


• When it receives the SID, the phone compares it to the SID programmed into the phone. Msci headquarters If the SIDs match, the phone knows that the cell it is communicating with is part of its home system.

• Along with the SID, the phone also transmits a registration request, and the MTSO keeps track of the phone’s location in a database — this way, the MTSO knows which cell you are in when it wants to ring your phone.

• The MTSO communicates with your phone over the control channel to tell it which frequencies to use, and once your phone and the tower switch on those frequencies, the call is connected. Msci world small cap Now, you are talking by two-way radio to a friend.

• As you move toward the edge of your cell, your cell’s base station notes that your signal strength is diminishing. Msci world free index Meanwhile, the base station in the cell you are moving toward (which is listening and measuring signal strength on all frequencies, not just its own one-seventh) sees your phone’s signal strength increasing. Msci world index total return The two base stations coordinate with each other through the MTSO, and at some point, your phone gets a signal on a control channel telling it to change frequencies. Msci world index This handoff switches your phone to the new cell.

As you travel, the signal is passed from cell to cell. Msci eafe index ticker Let’s say you’re on the phone and you move from one cell to another — but the cell you move into is covered by another service provider, not yours. Msci world materials index Instead of dropping the call, it’ll actually be handed off to the other service provider.If the SID on the control channel does not match the SID programmed into your phone, then the phone knows it is roaming. Msci world price index The MTSO of the cell that you are roaming in contacts the MTSO of your home system, which then checks its database to confirm that the SID of the phone you are using is valid. Msci full name Your home system verifies your phone to the local MTSO, which then tracks your phone as you move through its cells. Msci ipd And the amazing thing is that all of this happens within seconds.

The less amazing thing is that you may be charged insane rates for your roaming call. Msci world index bloomberg ticker On most phones, the word “roam” will come up on your phone’s screen when you leave your provider’s coverage area and enter another’s. Msci us index If not, you’d better study your coverage maps carefully — more than one person has been unpleasantly surprised by the cost of roaming. Eafe msci Check your service contract carefully to find out whether you’re paying when you roam. Msci world tobacco index Most of the larger phone companies do not charge for roaming within the U.S., but some of the discount companies do.

Internationally is another story. Msci world performance The roaming rates can be very high, assuming you have a phone that can work in multiple countries. Msci world index data Different countries use different cellular access technologies. Msci eafe value index More on those technologies later. Msci global index First, let’s get some background on analog cell phone technology so we can understand how the industry has developed.