Understanding VoIP

VoIP seems like magic to many otherwise competent technical folks. I think its because we've been brainwashed by the phone companies for almost a century into believing that voice is hard or different. I'm happy to report that its not true. On this page, you'll find specifications, tutorials, open source software, and other resources you can use to understand VoIP.

Useful Information

SIP is a signaling protocol.

• SIP initiates the call and tells the end-points how to talk to each other.
• SIP does not process the call itself
• SIP is an HTTP-like request-response protocol.

• The media path (i.e. the path the call takes) is likely different from the signaling path.

To talk between an IP phone and the PSTN, you need a gateway.

• A gateway is not a SIP proxy.

Media Refeferences

• Why the Bells Should be Very Scared - Business Week article on the rise of VoIP.

Tutorials and Reference Websites

• SIP Tutorial - a 187 page PDF slideshow that is full of useful information about how things work and the protocols that make it go.

• VoIP on Linux - I was hoping this was going to be a tutorial, but its mostly a cheerleading piece on why Linux is a good choice for deploying VoIP solutions.

NetworkWorldFusion on OSS - Operational Support System. .

• Describes the computer systems used to provision, bill, manage and inventory telephone-related products and services. Over time, the basic automation was linked into other functions, like customer relationship management and workforce administration.

• Megaco Standard Article from NWF

• Emergency Numbers and SIP Resources

Open Source VoIP Projects

• SIP Express Router - a high performance SIP server.

• Asterisk - Open source PBX project

• B2BUS - the back to back user agent can act as a user agent client or a user agent server. INcludes a pre-paid billing application.

• Cistron RADIUS Server - An open source RADIOUS server for authentication and authorization.

• SER Web - web interface for administration and self-provisioning of SIP Express Router users.

Softphones

• Xten - Softphones for Windows, Mac, and PocketPC. X-Lite is a free version that seems plenty good enough.

If you enjoyed this article, consider subscribing to my RSS feed or signing up for my free newsletter.

Last Modified: Friday, 31-Dec-2004 19:48:50 MST