ion, but even so, the cost of expansion can be significant and may involve the change out of both software and circuit boards. If you are considering a system from a particular manufacturer, looking at their entire product line can provide you with insight into their strategy for providing systems to organizations of vary- ing sizes. A few of the larger manufacturers (such as Avaya, formerly Lucent, formerly AT&T and NorTel, formerly called Northern Telecom) provide systems for 5 telephones up to sys- tems with 10,000 telephones or more. While the smaller systems are overall less profitable, there has been a need for the big com- panies to compete with the manufacturers of smaller systems to keep their customer base intact. Most very large organizations have small locations as well, SO for a manufacturer to provide complete coverage, it must of- fer the smaller systems. 30 to The Telecom Handbook CHAPTER 2 Many other manufacturers target a more limited range. There are many more manufacturers of smaller telephone systems (ei- ther PBXs or more basic systems sometimes known as "Key Systems") than of large systems. Only 4-5 companies go up to the 10,000+ telephone sizes. How the PBX Works What Happens to your Voice at the Desktop Your voice is converted to a digital form within the desktop telephone before it is sent over the cable to the PBX in the tele- communications equipment room. The device in the telephone that converts your analog voice into a digital signal is called the codec, which stands for "coder- decoder." It is this same device that converts (or decodes) the digital signals back into the recognizable voice of the person with whom you are speaking. While the PBX and telephones are evolving to a different technology known as IP (Internet Protocol) the codec in the tele- phone is still the device used for translating digital signals into human voice for sending (speaking) and receiving (listening). PCM (Pulse Code Modulation) has traditionally been used in most PBXs that are now slowly making the trans