Need VoIP? DIY with Asterisk

Part One: Asterisk offers a free and powerful VoIP PBX that can scale up to enterprise networks.

By Carla Schroder | Posted Nov 22, 2005
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Unless you've been living in a cave, and sometimes that's a very appealing notion, you've heard the buzz around Asterisk. Like so many Free and Open Source software projects, the name is only obscurely connected to what the product actually does. (On the upside, it's a nice, pronounceable word, and is not a silly recursive acronym like GNU or WINE or LAME or PINE.)

Asterisk is a feature-ful, flexible Free (GPL licensed) PBX (define) server. It officially runs on Linux, and has been successfully used on other Unixes (BSD, Solaris, OS X, and so forth) as well. Asterisk frees you from the tyranny of expensive commercial PBXs, and gives you complete control over your telephone services. It's easily adaptable to either business or home use.

Asterisk works with POTS (Plain Old Telephone Service) and iPBX (Intranet Private Branch eXchange), which is another way of saying VoIP (Voice over IP). Asterisk does all the usual business telephone stuff, plus new advanced things:

  • Voicemail
  • Extensions
  • Music on hold
  • Send voicemail to email
  • Conferencing
  • Caller ID (where the telco supports it)
  • Interactive Voice Response
  • Call Queuing
  • Voice-over-IP
  • Call Forward on Busy
  • Call Snooping
  • Call Waiting
  • Caller ID on Call Waiting
  • Distinctive Ring
  • Text-to-Speech

And loads more. Visit Asterisk.org for an exhaustive (and exhausting) list.

Why Bother?
Well now, that is a good question. Getting into telephony is a tangled thorny thicket of open standards, closed proprietary standards, proprietary devices with weirdo proprietary operating systems and commands and a whole new bale of jargon to learn. But if you're already into having control of your computing infrastructure, taking charge of your telephony is a natural progression. And, a nice side effect is it will increase your knowledge and skillz as a networking guru, since telephony is a fundamental basis of computer networking.

Because Asterisk is both Free Software and free of cost, you can dink around with it in all kinds of ingenious ways. Like building a phone system for your home with all the features of commercial PBXs that cost thousands of dollars. You can have very cheap long distance, internal extensions, transfer calls, and something that I like a whole lot- sophisticated voice mail under my control, and not costing me a monthly fee. Callers will never get a busy signal; they'll either get a human or the voicemail. You can even torture them with complex phone menus with too many options: "To record a compliment, press 1. To leave a complaint, press pi divided by the radius of the Earth's orbit around the sun."

Fun With Office Space
A common scenario in commercial office buildings and office parks is all tenants rent a piece of a big shared PBX. This has its upsides: it reduces costs and hassles. But the downside is you're at the mercy of whoever runs the system. Here are a couple of my fave True Shared PBX Horror Stories:

One office park that I worked in used the same default password for all new users, and left it up to the users to reset the password. Naturally most of them didn't bother, which created fabulous exploration opportunities for inquisitive persons. It's quite amazing what people will say on an office phone, and record on office voicemail. And hypothetically, the aforementioned inquisitive persons could have all the free long-distance their little hearts desired.

Another commercial building that I had the (dis)pleasure of working in I swear hired random strangers off the street to administer the PBX. Nothing worked, and no one knew the admin password. Tenants learned to pick the lock on the phone closet to try to fix things, and some of them got pretty good at it. The problem of the lost admin password was solved when someone discovered the hard-coded default vendor password. (Hurrah for the Internet. Nothing stays secret for long, including secret vendor backdoors. Shame on you.)

Planning Asterisk
There are a lot of questions to be answered before you rush out and slap up a nice Asterisk PBX for your office: what functions do you want? Are you prepared to buy some new equipment? Are you ready to learn a whole new vocabulary? Let's take a look at some of the ways to put Asterisk into service.

Using Softphones
Asterisk comes ready to perpetrate IP-based telephony. This is where you get the most features and save the most money. All you need is the Asterisk server, "softphones" for users, and ordinary Ethernet. If you're only using this on your LAN or WAN, making voice calls PC to PC, you don't need a commercial VoIP provider. If you want to be able to call anyone anywhere, including people on regular analog lines, you'll need a commercial VoIP network like Vonage, Broadvoice, Covad, Skype, or Speakeasy. There are a lot of these, so it pays to shop around. Prices vary, and some place limitations on the equipment you can use.

Softphones are software applications that turn any computer with a soundcard, including PDAs, into VoIP phones. Plug in a headset, and away you go. Softphones are available for Linux, Windows and Mac.

Putting a soft phone on a laptop means you can take your account with you when you travel, and make VoIP calls from anywhere. Anywhere that your provider's network reaches, that is, or directly to your LAN.

Relying on a PC just to talk on the phone has its drawbacks, of course, such as the lack of portability, and needing an entire computer just to make a phone call. This works great in call centers, and for any job where users are pretty much chained to their desk all day. It's also the easiest and cheapest way to test and get the hang of Asterisk.

You can also get normal-looking telephones that support the VoIP protocols. Asterisk supports many VoIP protocols, and there are a lot of them – what you want to look for are "SIP (Session Initiation Protocol) Compliant Handsets." The SIP protocol is the most reliable. These cost anywhere from under $40 to over $1500. You can even get wireless handsets. VoIPSupply.com and Voxilla are examples of fun places to check out equipment.

Plain Ole Telephones
Asterisk also supports standard analog telephones. Analog phones require adapters, like the popular Sipura adapters.

Cutting Out The Telco
A lot of folks in these here modern times don't even bother with land lines – they rely completely on cell phones. But what if you want a land line as a convenience or a backup, without paying a bale of money for something that you hardly use? For example, out here in the middle of nowhere I'm paying almost $35/month for basic local phone service. No caller ID, no voicemail or other extras, and the local calling area includes maybe 3000 people.

Asterisk can do it, if you have cable Internet, ISDN, T1, or such. (If you have DSL you have to pay for a land line anyway.) Sign up with a VoIP service provider, wire up your home PBX, and away you go. For example, Broadvoice offers a $19.95/month plan that includes unlimited calling to 21 countries, which includes all the bells and whistles that telcos charge all kinds of money for, like caller ID, anonymous call rejection, call managers, and so forth.

Come back next week to learn how to set up a simple Asterisk PBX.

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