Generally, pager networks are established in coverage 'cells'. It is equivalent to throwing a piece of graph paper over the area which is desired to be covered. Sprinkled around geographically strategic sites in the cell are transmitters (or 0 if it is a REFLEX cell) attached to telephone poles or lamp posts. Of course, a proprietary three-letter acronym must be invented to label this "new" kind of device so that it sounds impressive. In pager-speak, the transmitter/transceiver unit is called a remote terminal unit, or RTU. A picture of a typical RTU can be seen below in Figure 1.

Figure 1: Typical RTU

Due to unpredictable electromagnetic conditions in the atmosphere, cells and RTU's generally overlap. Additional receiver hardware is usually necessary to contend with the possibility of receiving data from two sources. The simplest pager network possible consists of a single, stand-alone RTU. A number of restaurant chains, such as The Outback, Cucina Cucina and Steak 'n' Ale use single RTU networks to notify waiting customers with tone only pagers when their table is ready. However, these a single RTU is quite limited in range and is extremely susceptible to electromagnetic noise.

Usually, RTU's are connected to a "cellmaster" or "cell controller." These distribute data and synchronize the transmission times of the multiple RTU's which form a cell. Due to the long haul distances which are involved in the communication links between the cellmaster and the regional pager network controller, data tends to be multiplexed over multiple fiber optic or copper lines. The task of demultiplexing is usually performed by the RTU and transmitted over coaxial transmission lines to the RTU's which are enslaved to the cellmaster. The cellmaster, like the RTU, is also a field mounted device. A picture of a typical cellmaster can be seen below in Figure 2.

Figure 2: Typical MCC

Data for a pager network originates from a network controller, sometimes referred to as a wide area network (WAN) manager. Any number of MCC's can be hooked to a single WAN manager. From the diagram shown in Figure 3 below, pager networks are clearly based on the star topology. As with all networks of this type any number of levels of indirection can be implemented. Thus, a regional or local WAN manager can be enslaved to an even bigger WAN manager. The central hub is always hooked to numerous land phone lines, the Internet as well as various other methods by which people can send pages.

There are two popular methods of encoding digital data for transmission to and from pagers. One is called frequency bit encoding (FBE) and the other is phase bit encoding (PBE). A visual comparison of the two methods an be seen below in Figure 4:

In the FBE algorithm, zeros and ones are transmitted as different frequency waves. The frequencies which represent zeros and ones should be sufficiently distinct such that any frequency distortion which occurs between the transmitter and receiver can be dealt with. The PBE method encodes zeros and ones in phase changes. No phase change represents a zero in this case, and a 180 degree phase shift is an encoded one. One should take notice that both the FBE and PBE methods do not reference the amplitude of the signal in their encoded data. This is particularly important in the field of wireless communications where the amplitude of the signal can often be distorted beyond any kind of recognition.

The general method of data transmission to pagers resembles a bus. Packets of data meant for different pagers are sent out by the main WAN controller to the local MCC units, which in turn distribute to the RTU's for transmission on a specific frequency. Up to a few million pagers are all tuned to a precise frequency band, something like 916.3 MHz. All of these pagers receive every packets broadcast in the frequency band they are tuned to. The pagers have hardware which then decodes the packets to determine where the packet was intended for. In the POCSAG protocol, the address is a 31 bit number with a checksum. This allows roughly 2 million pagers to be tuned to a given frequency band. Motorola has yet to disclose the number of bits allocated to addressing in the RE/FLEX protocol. Regarding bandwidth, the POCSAG protocol originally transmitted at 300, 1200 or 2400 bps depending on the type of RTU used. The RE/FLEX system operates at 300, 1200 and 2400 baud to maintain compatibility with older POCSAG transmission hardware as well as at 4800 and 9600 bps for two way transmission.