In part 1 of our blog series, we defined three main telephony technologies

• Analog Telephony,
• Digital Telephony and
• IP Telephony.

We then examined Analog Telephony and looked at the reasons why businesses would want to continue using Analog telephones. 
In part 2 of the series, we continue by exploring the second generation of business technologies: Digital Telephony.
 

Part 2: Digital Telephony

During the 1980s and 1990s a revolution in technology entered the world of telephony.  This became known as the “digital age” of telephony as digital multi-line phones quickly replaced analog phones. Initially digital phones being more expensive were only used for executives, service desks or reception desks. That all changed as the price of digital telephones came down in cost in the late 1990s and digital phones started to surpass analog phones in all settings. With digital telephony, analog signals are encoded digitally and these digital messages are sent over the digital lines to be reconstructed back into audio at the handset.

Improved Voice Quality

Digital telephones introduced a whole new realm of audio to a typical telephone call.  While analog lines are clear, digital signals are cleaner. Especially when making announcements over speakers, like in a retail store when a page is made from a digital telephone, the call terminates with a clean silent release from the phone line….with no clicking or popping heard over the speakers.   

Reliability

Digital phones use very little power, and it is drawn from the phone line itself. The wiring is simple, the phones are robust and the setup is not complex when compared to IP technology. Once the phone is installed, there is very little that can go wrong.

Features: Displays and more!

Digital telephony opened up a new capability; the ability to provide a display or screen that would display a wide range of “intelligence” that was not available with analog.  This information grew more sophisticated and second nature.  We forget prior to digital telephony the only way to know who was calling was to answer!  Let's take a look at some popular features for digital phones.

For Installers

From an installer’s perspective the most desirable features are:

• Display labelling of keys
• Set-based configuration and
• Simple and intuitive provisioning interface.

For Users

From a user's perspective (depending on the type of user), these features are highly desirable:

• Busy Lamp Field (a.k.a. Boss-Secretary Filtering) – this feature provides a visual indicator (a.k.a. presence), click-to-dial and call screening all on the same key.
• Set-to-set paging (a.k.a. Voice Call/Intercom Call) - this feature allows users to page others via the handsfree speaker on the receiving phone.
• Interactive display – the display screen can show if you have missed calls, if you have a voicemail, the time and date, and incoming caller information.
• Shared Call Appearance - this feature allows multiple devices to share the same line key

Cost: Multi-Lines and Shared Lines

A multi-line analog phone requires a physical cable for each line connecting directly to the phone. With digital telephones, only one physical cable connects to the phone and it can handle multiple lines. A digital telephone system also allows you to share a pool of lines that can be accessed by dialing an access code (sometimes called a trunk access code) such as “9” to access an outside line.  With the analog multi-line phones, you had to manually select the outside line you want to use and then dial out. There is significant cost savings here when phones can share a pool of external lines.

Why use Digital?

Digital phones still exist in many places, but they are fast being outpaced by VOIP based telephones, or more commonly referred to as IP Phones.  Many of the digital telephones on the market from the 1980s and 1990s, such as the AT&T 7400/8400 series or the Nortel Meridian M2xxx/M3xxx series or the BCM Norstar M7xxx/T7xxx series, still perform well. Their voice quality and features continue to work flawlessly and are still very much sought after by businesses.  The only reason most of these phones are being pulled is the fact that they may be perceived as outdated or the users are tired and they want the newer display of an IP phone.  Some firms may be worried that their digital telephones aren’t supported anymore because the big IP system vendors sometimes use scare tactics to tell users that their digital telephones will fail if they don’t switch to their new IP system.  In reality, the market continues to support older systems with parts and software, such as the Meridian 1, Lucent/Avaya Definity, Meridian Norstar, and other large 1990s PBX’s which are still maintained and offered by many vendors.  Companies like E-MetroTel, Avaya and Mitel support a hybrid of digital and IP phones, allowing you to bring digital telephones over to their platform and combine them with IP phones. Note that the cost of digital telephones are much cheaper compared to IP phones.

Summary

If you are considering replacing your phones, do some research first.  Decide if you really want to rip and replace everything, or it could be more economical to keep your best digital telephones and then upgrade as needed. One such option would be to upgrade some users to IP phones, an idea we will explore in depth in Part 3: IP Telephony.

	Analog	Digital
Voice quality	♦♦♦	♦♦♦♦♦
Reliability	♦♦♦♦♦	♦♦♦♦♦
Features	♦	♦♦♦
Cost	♦♦♦♦	♦♦♦♦♦

References

1. https://www.linkedin.com/pulse/20141009164554-77575399-digital-phones-v-ip-phones-what-s-best/
2. http://stgcommunications.com/next-phone-system-digital-voip/