The Joy of SIP

It’s hard to thing of a technology that has more fundamentally revolutionized the way we do things more than IP telephony, and SIP in particular.

Back in the early 1990s, I was charged with installing a telephone system in an office building that would house 50+ users. I had to buy an Ericsson PABX, which took up an entire corner of the comms room, pull up all the floor panels to route new cables to the desks, buy all sorts of expansion cards to accommodate voicemail and PSTN interfaces, and buy 50 bulky handsets so that users could actually use the thing from their desks. I then had to go off to ESAT and get 8 actual telephone lines, which took 4 weeks to get installed. The whole project cost about €17k, and that was nearly 20 years ago.

Let’s compare that to my most recent installation of a telephone system, earlier this year, again in an office of approximately 50 users.

For the PABX, I bought a tower PC from Amazon which cost €299. I installed the OpenSource software PABX, Asterisk, on this, which took about 20 mins. I then purchased a business package from the VOIP provider, Blueface, which included 8 dedicated Direct Dial extensions, which took about 30 minutes. I then configured Asterisk to use the Blueface SIP trucks, which took another 30 minutes.

Next to handsets. Did I buy 50 handsets?

No, not this time.

This time I purchased 1 handset for the main office number, which cost €99. For everybody else, we installed a SIP Client on their mobile phone, such as CSipSimple, and allocated an internal extension to everybody who wanted one. This client connects to Asterisk over the office’s main WIFI network.

Basically, that means that everybody’s mobile phone doubles up as their internal office extension. When somebody rings their extension, their mobile phone rings, or when they want to make a call, either internally or externally, they use their mobile phone. Any external calls they make are charged to the company via the Blueface account. In addition, all users are now fully mobile, so if they are in a meeting in another part of the building, they can still be contacted on their internal extension.

This company also has external IPSEC VPN access, so for users who are on the road a lot, I installed a VPN client on their phones, which means they can use their internal office phone extension from anywhere in the world, whether they are on a WIFI/3G/LTE connection.

This company is also multi-site. They have offices in different continents, linked together by a VPN. That means that if a manager is on trip to the office in another continent, they can still be contacted on their internal extension, all over IP, because their mobile SIP client is connected into the main corporate LAN over the WIFI.

Meanwhile, that PABX I bought way back when is probably still rotting in a landfill somewhere.

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