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The answer is simple.  You can add digital, analog, and VoIP.

Digital Telephone Stations

The most common telephone stations in use on business telephone systems are digital.  Some examples of pure digital systems include Norstar phone systems, Avaya Merlin Legend and Merlin Magix, and Avaya Definity systems. Digital phone systems sample your voice using a method called Time Division Multiplexing or TDM.  When you speak into a digital telephone, your voice is digitally sampled into time slots so that a conversation doesn’t have to use the entire bandwidth of a circuit.  The system then uses a clock to synchronize the digital samples and turn them back in to voice.   That sounds complicated.  It is, and you don’t need to know what it means.  Whereas analog telephone stations can only handle one conversation at a time, digital phone stations can stuff more than one conversation and other features onto a single pair of wire.  This provides for more features, less wiring, and more efficient communication than a simple analog circuit.

When shopping for a digital telephone system, you may encounter a variety of acronyms describing the names of each manufacturers digital protocols.

Avaya Phone Systems – DCP – Digital Communications Protocol, MLX – Multi Line Digital, TDL – I don’t remember what this one stands for.

Norstar Phone Systems – TCM – Time Compression Multiplex

Toshiba Phone Systems – DKT – I don’t remember what this one stands for.

Analog Telephone Stations

An analog telephone station uses no digital sampling to compress your voice and conserve bandwidth.  When you use an analog telephone the sound waves of your voice are converted into electrical waves by a microphone and conducted down copper wire.  The telephone of the person you call then uses those electrical signals to vibrate a speaker in their phone’s handset.  The speaker then moves air and produces sound waves that can be heard.  When you use an analog phone and connect to another phone, you seize the entire circuit.  No one else can use that circuit while you are conversing.  The same is true for analog telephone stations connected to a business phone system.  They can only handle one conversation at a time.

There really aren’t any completely analog business telephone systems manufactured anymore.  The AT&T Merlin phone systems were probably the most popular analog phone systems ever produced.  The majority of these were installed in the 1980’s.  There are still many of them still in service today.  Merlin phone systems used an ATL (analog telephone line) standard of 4-pair (8 wires) copper wiring that connected the Merlin control unit to each telephone.   Today’s digital systems only use a single pair wiring scheme that can handle much more voice and signaling information over less wiring.

Well, then what are analog telephone stations good for?  Today’s digital phone systems can all handle analog stations.  Analog phone stations are usually seen in common areas like a warehouse, lobby, or lunch room.  Fax machines and modems are also forms of analog phone stations.  One of the most powerful uses of the analog phone station is the conference room speakerphone.  You may have already used some of these futuristic-looking triangular speakerphones.  The most common is the SoundStation series by Polycom.

Voice over IP Telephone Stations

VoIP phone systems are creating all the buzz.  Most manufactured phone systems today boast VoIP capabilities and can handle IP phone stations.  By converting voice into data packets, these phone systems can send voice conversations over a business’ data network.  No more need for separate wiring in the wall.  One set of wiring can handle the data network and voice network.

Conceptually, this is great from a physical wiring and management perspective.  There is less investment in wiring and conceivably one person/department can manage both the phone system and computer network.  The telephone system after all becomes just another application on the data network.

The most important application provided by today’s VoIP capable systems is telecommuting.  An employee no longer needs to be in the office to use the phone system.  VoIP phones can connect to the home office phone system via VPN (virtual private network) over the the public Internet.  The employee can make and receive calls as if he were in the office.

So, what kind of telephone stations should I add to my phone system?

If you end up purchasing a currently manufactured system, then it will be either digital or digital and VoIP.

Digital Phone System – If you purchase a solely digital phone system then you will add digital phone stations and probably some analog ones in the situations we described above.

Digital and VoIP Capable System – If you purchase a system that handles digital and VoIP, then there are some choices to be made.

• Situation 1 – Your office space already has existing phone wiring from a previous phone system.  Choose digital stations.  Digital telephone stations have somewhat better sound quality than VoIP.  You may also save money because VoIP phones often require additional hardware and/or licensing.
• Situation 2 – You are wiring a new office space with one set of wiring or your existing office space only has one set of wiring for the data network.  Choose IP stations. IP telephones can share the wiring for the data network.  Most IP phones have built-in 2-port switches so that each phone can be connected to a co-located PC for the employee’s work station.