| Session Initiation Protocol (SIP): FAQs, background materials and lists of current work in this field. |
| Brekeke Software: Products for small to medium sized offices and a server database. |
| FirstHand Technologies: Client and server software developer for service providers and telecom equipment vendors, to address enterprise mobility markets. |
| IETF SIP Charter: Working group for protocol development. Links to RFC's and internet drafts. |
| Parrish Systems: Sells off the shelf code and provides a software consultancy service. |
| PROTOS Test Suite: A test-suite to find vulnerabilities in protocol software. |
| pulver.com: A collection of information on the protocol. Contains news, reports and an IP telephony job noticeboard. |
| SIP Compose Group: A working group experimenting and documenting the protocol. Contains various internet technical resources. |
| SIP Forum: A membership based forum. Also contains a news board. |
| SIP Made Easy: An introductory tutorial talks about protocol functions, components, message types, how it works and where it is applied. |
| SIP Wiki: Wiki based resource containing information and links. |
| SIP411 Directory Services: A Yellow Pages style directory of SIP addresses. |
| SIPfoundry: An international open source community providing VoIP solutions and technology based on the SIP standard. |
| Soft Front: Provides a software development environment. |
| Tech Invite: Portal containing links to technical information and RFC documentation. |
| The SIP Center: Portal with technical and market resources aimed at commercial developers. Also provides a testbed area for software and proxy development. |
| Vidosystem: Produces softphones. Site has downloads section and information on protocols supported. |
| Voice System: Design, consultancy and development for SIP Express Router (SER) servers. |
| VoIP News: Information on available technologies and software/hardware product reviews. |
| VoIP User: Consumer guide and forum. Also has software phone downloads and links to service providers. |
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