Introduction And Definitions
According to a report released in March, 2002 by New York City-based Scarborough Research, 62 percent of Americans owned a wireless phone, up from 55 percent in 2000. The CTIA (Cellular Telecommunications Industry Association) reported in April of this year that 70 percent of the US population had and used cell phones in 2006. While growth wasn't as spectacular between 2002 and last year, the CTIA report shows a huge number of users, 208 million.
The following is not to brag, but to let you know that I have a strong and serious background in wireless public networks. I am a former employee of "Sprint Together with Nextel". I started out in customer service in a call center that mostly handled technical support. In that environment, my knowledge expanded to the point where need to make very few requests for backup from the tech support department. Later, when Sprint released their PowerSource service (phones and services that used both the Sprint and Nextel networks - which is an engineering feat), I was one of 18 agents trained locally for specialized customer service. I was also trained for technical support and assigned to that department towards the end of my stay with Sprint. I handled escalated issues as well, and when I left, I could take any call that came in the building and almost always resolve the issue.
These are some definitions for common components of the mobile phone system. I will quietly introduce more definitions later as needed.
The Basic Network
Though the details might vary by carrier, the diagram below shows the basic components of a wireless public network. The subscriber makes a call to a tower. The call is sent on to a switch. The switch authenticates the wireless phone to assure the phone is allowed to make calls through the carrier's network. Authentication is done through what is called a "Global Home Location Register" (GHLR). The GHLR, a separate component, is not shown in the diagram. Once the phone is authenticated, the switch places the call, which is sent either to a wired (land line) or wireless phone. The network then supports a 2-way conversation between the two phones.
Call flow on a basic network; details vary based on carrier. Click the image for a larger version.
A single tower provides coverage over an area of 7-10 square miles. I won't get into satellites at this time because most wireless public networks don't depend on satellites, though they may play a role in the big picture.