Analogue extensions have been around as long as PBX’s have. In fact my old analogue phone I had at home years ago was really an analogue extension off the Public Switch (also a PBX).


Interestingly there has always been a need for analogue. Back in the late 80’s I supported an old PBX that did only digital extensions, thats right, no analogue extensions. I had a hard time trying to explain to customers how their analogue lines (FXO) were terminated to the PBX and yet there were no fax or modem capabilities. Fast forward to early 2000 and I found myself in a similar position. The technology had advanced and the brand was different, but the story was the same. 


In the past, why so prevalent?

Although analogue has always been (some what) supported it is often times limited. This meant that you had to have very clear reasons for going analogue on any extensions. Often it was the fact that digital extensions could not exceed 1000 ohms impedance on the copper line whereas analogue could go up to 8000 ohms (if memory serves correctly, and boosted to twice that with the correct hardware). That made analogue the go-to endpoint for larger sites and factories etc. For this reason those long range outdoor extensions were always analogue.

Perhaps the extension was in a noisy environment and a loud ringer was required. Another reason was that the CPE (customer premise equipment had some sort of legacy modem function, like an older printing press or something like that. And it needed to report its status to a central server over its built-in dial-up capabilities. 

Even back then, if you wanted any flash features you had to go digital. It was clear that the proverbial writing was on the wall for analogue extensions. Or was it?


Lync and Analogue

What ever the reason, I still find today in 2014 that analogue just won’t die. No matter how much you attempt to reduce the number of analogue devices, somehow there is always still one hanging around.

So why would you avoid analogue devices in a Lync environment you may ask. Firstly let me start by stating that I am fully aware that analogue devices can be configured in Lync. Its far more elegant than previously when all analogue had to be configured and managed via voice gateways (you still need gateways for analogue).


Why not analogue?

Just as in the days of the old PBX, if you want flash features you will need to move away from analogue. Here are the common reasons I raise when a decision needs to be made:- 
  • Limited or No features, its really everything beyond dial tone(the ability to make and receive calls). For example, transfer, forward, follow me, conference etc. If you want to leverage any more than that the gateway needs to provide these (If possible). Many gateways do not provide feature functionality to the FXS ports.
  • No Presence information. I have had a play with SmartSIP from Sonus, as far as I could tell the SmartSIP presence was for presence information from non-Lync SIP devices and excluded analogue (FXS).
  • You can’t manage analogue devices from the Lync Control Panel (you have to use Lync Shell).
  • The Dial Plan policy applied for analogue is limited to Site or Default (Global)
  • If migrating to SIP Trunks for Lync, keep in mind that many ITSP’s don’t support FAX\Alarm over SIP. This means that you may still need to maintain analogue or ISDN trunks per location for this purpose.


When do you need analogue?

When is there little choice? Same reasons as back in the day. These are the reasons I commonly encounter:
  • No infrastructure to drop the endpoints on the network, only old(er) copper
  • Must have FAX (I strongly suggest looking at fax to email or FAX servers here)
  • Legacy equipment required by machinery for reporting alarms etc.
  • Any legacy equipment (eg Auto dialers, Gate phones etc*)
  • Loud ringers*
  • Elevator phone* (I still haven’t come up with a small factor IP phone to replace these)
  • Alarms (I suggest these are terminated as POTS lines, removes the power dependence in the event of an alarm is triggered when power is out)
*I have come across a variety of non-Lync SIP devices that cater for some of these scenarios, these devices however will need to register to a gateway to connect to Lync.


Please Contribute

I would love to hear about your experiences with Lync and analogue extensions. Perhaps you can contribute to the list of reasons for or against. Also if you have a good replacement for any of the traditional usages, I’d like to hear from you.


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