| The history of cell phones finds its birth around | | | | cell. The landline telephone network is also |
| 1980. A batch of approximately 2000 mobile | | | | connected to the towers. When you call someone |
| phones was manufactured in Chicago. The | | | | on your handset, it searches for a signal from a |
| intended customers were given a free phone to | | | | cell tower. |
| see if that type of business would work. They | | | | If your handset cannot find a signal you will not |
| were not the first cell phones manufactured, but | | | | be able to make a call. A major requirement for |
| they were the first to be mass produced. | | | | all cell phones is to have a System Identification |
| The users found it so convenient to be able to | | | | Code, SID. It is a unique five digit number. The |
| quickly and easily call someone from wherever | | | | FCC assigns this number to each carrier. |
| you were at the time. The initial cell phones were | | | | The SID code is put into your handset after you |
| wieldy and cumbersome. In addition, they were | | | | sign a service contract. Then the phone is |
| unsightly as well as expensive. | | | | activation. When you turn your mobile phone on it |
| Today the cell phone industry generates an | | | | searches for a SID on the control channel. Your |
| astronomical $120 billion in revenues. That | | | | cell phones inability to retrieve it results in the |
| constitutes an apparent mega monster in | | | | dreaded no service message being displayed on |
| anybodys book. Should one or two cell phones go | | | | your phone. |
| awry, it would beunderstandable in light of the size | | | | Conversely, should a SID be found, the SID in the |
| of the networks. | | | | handset tries to match up with the SID that was |
| However, in most cases you can still rebook a | | | | located. When a match is made your cell realizes |
| return flight to Hawaii while at the same time | | | | that it is working from home base. |
| make a weather check in Boston. As far as | | | | Should they not match up, your mobile is said to |
| communication is concerned, todays phones are | | | | be roaming. The system manager that your |
| versatile and worth their weight in gold. | | | | phone is roaming in, contacts the manager of |
| It appears as if there is not much behind one | | | | your home system. Then your system manager |
| mobile call because they are so easy to make. | | | | checks its own database to confirm that your |
| However, just attempting to explain the wireless | | | | SID is valid. Your phone is then tracked as it |
| networks can get perplexing. In point of fact, the | | | | roams through the various cells. Using someone |
| wireless networks are a string of radio towers. | | | | elses network like that means added costs. The |
| Only a few miles separate each tower as they | | | | truth of the matter is roaming can hurt your |
| form what looks like a vast grid. | | | | pocket. |
| The space from one tower to the next is called a | | | | |