Asterisk is a PBX in software.

Links provided by Chris:

Here are some basic links that cover both VOIP and the Asterisk project as well as the grandpa of all VOIP stuff, pulver.com (Free world dialup)

  • The Asterisk project
  • Digium (the sponsors)
  • The VoIP-Info Wiki
  • Asterisk section of the Wiki
  • The Howto
  • Sprackett Asterisk Page
    • General
  • Pulver.com / fwd

    • Articles

  • OnLamp Article

    • Presentations

  • Zac Asterisk Talk 2004

    • Terminology

    PBX - Private Branch eXchange

    SIP - protocol for setting up and tearing down sessions (can be audio, video, chat), works over TCP or UDP, does not include the audio streaming, modeled after HTTP

    VoIP - Voice over IP

    H.323 - the audio streaming protocol standard for VoIP?

    AGI - extension API for Asterisk, similiar to CGI, Asterisk will call scripts and pass input/output over stdin/stdout

    xAP Protocol

    Mark writes:

    xAP is a protocol for Home Automation.

    It's human-readabale, goes over a variety of transports including IP (but also RS-232, RS-485, 1-wire, etc.), and deliberately isn't XML. The reason it's not XML is one of size, and therefore latency over the slow communication links.

    It's a community initiative rather than coming from a specific manufacturer or consortium. The Asterisk xAP-plugin is written by an independant developer rather than any of the original Asterisk team (go OpenSource!).

    To dial a number from outlook, you send a message which looks a bit like the following on UDP broadcast port 3639 (an official IANA allocation to xAP): 

    xap-header
{
v=12
hop=1
uid=FF123400
class=outlook.dialer
source=rocket.outlook.contact
}
Dial.cmd
{
Number=+441234675757
}

    The receiving xAP connector on the asterisk box reformats the number from international format through the application of the appropriate locale-specific dialling rules, and sets up the call. The message can be extended to indicate which extension to ring on completion of call setup.

    Benefits of xAP

    (a) the ability to support multiple users without any complicated configuration,

    (b) the decoupling of asterisk internals from the call-related features - so if the asterisk interface evolves, or if OGo want to interface with XYZ pabx at some point in the future, they don't need to rewrite/retest the front-end elements of the solution.

    (c) the ability for other applications outside of OGo to leverage the same connectivity. E.g. the ability to pop up callers names on the screen using xAP desktop or log all outgoing calls using xAP db.

    xAP Links
  • xAP C Library

    • VoIP Clients

  • Kphone
  • Gnophone
  • PhoneGaim
  • X-Lite
  • Lipz4

    • FAQ

    Q: Does it integrate somehow with my non-VoIP PBX?
    A: I guess it could. In practice, for my business, it replaces it.

    Q: Can I use my existing phone?
    A: Yes. It uses (open source hardware!) cards for both trunk lines and extensions

    Q: Do I need to use my laptop with microphone/headset?
    A: Not unless you want to.

    Q: Would it integrate somehow with Apple iChat/AV?
    A: No idea :-)

    Q: Is there something like a phone number?
    A:There is exactly a phone number if you plug it into a POTS (Plain Old Telephone System) line. You can use it to dial either SIP or POTS numbers

    Q: Is there something like an "official" registry (like DNS) for Asterisk phone numbers?
    A: Lord no - it's not aiming to introduce a NEW directory service.

    Q: So what does a PBX do?
    A: It determines where to send the call and to whom in the office. Also it can reroute the call over the internet to anywhere you tell it to or to any other device. The server also acts as a host, so for true VOIP calls a remote user can connect to it and it automatically routes the call to either your computers softphone or a hardphone, what ever you have predetermined in advance either for that specific incoming call, or alternatively for all calls in general.