@ Work

Training Manager

Technical Education and Documentation (TED)

Cellular Infrastructure

Motorola, Mundelein Training Facility

The Switch

The Electronic Mobile Exchange (EMX) is basically identical to telephone office switch equipment but has been adapted to cellular use. The switch is what actually connects your call to a telephone land line. It takes the audio from your phone and puts it on the telephone system lines. It also performs billing functions (ultimately your cell phone bill), controls the cell sites, translates your dialed digits, and validates your call based on the feature package you purchased.  Its basically a big ass computer. In large cellular systems it's possible to have many switches which are connected together and hand off to each other as you roam between systems or even with in a large system. This is the piece of equipment I used to teach.

The EMX2500G

The EMX2500E

Old Analog Cell Sites

Here's some of the old analog Base Transceiver Site (BTS) equipment. These are the base stations your cell phone actually talks to.  Believe it or not your cell phone is actually a radio talking to a base station. Geographically BTS Cell Sites are laid out in honeycomb pattern, each BTS occupies a cell in that honeycomb, thus the "Cell Phone". As you move, your phone is handed off from cell to cell to cell.  In the case of analog BTS's the switch controls the cell to cell hand-off.  Motorola has discontinued manufacturing this equipment but we still support it in training as many 3rd world countries still use a lot of it.

Old Analog Cell Sites

More Old Analog Cell Sites

Digital Cell Sites

These are the modern digital cell sites using CDMA (Code Division Multiple Access) technology. Units on the left are indoor BTS's, units on the right are outdoor versions.  Again, this is the base station your PCS or digital cell phone talks to. One of interesting things about CDMA technology is that you can be on multiple cells simultaneously which makes for a very smooth seamless hand-off.  It also lends itself to the ability to triangulate the physical location of a cell phone call in process (think about the big brother uses of that).  With the old analog sites you had to break from one cell and then hand-off "make" a connection with the next cell site. Digital cell sites are not controlled by the switch as with the analog cell sites, they are controlled by the CBSC.

Digital CDMA Cell Sites

More Digital CDMA Cell Sites

The CBSC

In a digital cellular system the CBSC ( Centralized Base Station Controller) is what controls the digital cell sites.  The CBSC also connects to the switch as call validation, billing, and connection to land phone lines still needs to be accomplished by the switch.  The CBSC controls the hand offs between digital cell sites, decodes and encodes the digital audio, provides the control and maintenance point for the cell network, and transcodes 8-bit audio to 4 bit audio allowing the doubling of the number of audio paths between the CBSC and Cell Sites.  In large systems there may be several CBSC's which can also hand off to each other. 

The CBSC

The IN Equipment

The IN (Intelligent Networking) equipment performs the functions of HLR (Home Location Register), MR (Message Register), and IS-41 Protocol Converter. As the HLR the unit acts as a huge database for all cell phone subscriber records. As a Message Register is controls such things as cell phone voice mail boxes and short messaging services.  As an IS-41 Converter it provides protocol conversion between Motorola and competitor switches in cellular systems. Again, these are basically big ass computers. Tandem on the left is the older unit, Tandem was bought out by Compaq. The Compaq on the right performs the same functions and has the same capacity as the Tandem but takes up only half the space.  Additionally the Compaq on the right is only half populated.  Fully populated it would be equivalent to two of the Tandems on the left.

The Tandem

The Compaq

The SRP

 Now this is an interesting piece. The SRP (Surveillance Resource Platform) is a new piece of equipment mandated by the government to fight crime, mainly drug trafficking.  The SRP connects between the switch and the local law enforcement agency and allows the government to wiretap cell phone calls.  Yes, big brother has the capability to tap your cell phone calls now.  I can't tell you anymore about it or the government would have to kill me.