The capabilities and applications enabled by Session Initiation Protocol (SIP)—while nothing new to SIP developers, Internet Service Providers and the like—may not be so obvious to mainstream developers who do not yet use it in everyday coding. So, here's a crash course in SIP for those of you who want to become SIP developers. You seasoned SIP developers may learn a thing or two as well, and find some valuable SIP resources you may not know about.
For inquiring minds that don't already know, SIP is an application-layer control or signaling protocol for creating, modifying, and terminating sessions—including Internet-based phone calls, multimedia distribution, and multimedia conferences—on an IP network. SIP often is used as a signaling protocol for Voice over IP (VoIP). Other applications include voice-enriched e-commerce, Web page click-to-dial, Instant Messaging with buddy lists, and IP Centrex services.
SIP signaling, is based on the request-response paradigm. Stateful SIP servers, like Ubiquity's SIP Application Server (SIP A/S), have the ability to split an incoming call so several extensions can ring at once. Also, SIP returns different media types within a single session. For example, a single communication session can allow a customer to call a travel agent, view video clips of vacation destinations, book online and order currency.
With Internet, mobile, and the more traditional Public Switched Telephone Network (PSTN) coming together over an IP network, SIP plays a key role in establishing sessions that enable cutting-edge applications.
Resources at HandA primary resource for all things SIP can be found at The SIP Center, an extensive online resource dedicated to SIP developers. The SIP Center is an independent community resource founded by Ubiquity Software and supported by the industry's leading players as sponsors. You will find the tools, resources, and information you need to help you create commercial, SIP-based services and applications for the global telecommunications market.
The SIP Center details SIP resources available to you as a developer, including information you may need for developing SIP apps for mobile, desktop call management, e-commerce, gaming and instant messaging environments.
SIP-related ProtocolsThe SIP Center provides information about the various protocols related to SIP, as we previously mentioned. Under a section called Programming SIP, you can learn all about Call Processing Language (CPL), SIP Common Gateway Interface (CGI), SIP Servlets, and Java APIs for Integrated Networks (JAIN), including JAIN SIP, SIP Lite, and SIP Servlet. You will also find information about developing mobile applications with SIP, and learn about the Third Generation Partnership Project (3GPP) for producing globally-applicable technical specifications and technical reports for a third generation mobile system. You can also find out the latest information about using SIP with Wireless Application Protocol (WAP).
Get in-depth details about the various initiatives and protocols on the SIP Center protocols and initiatives page.
Developer and Testing ToolsThe SIP Center provides a plethora of resources and tools for SIP developers, such as:
Blogs
Codecs
Commercial SIP products and service providers
Developers programs and community sites
Free SIP and ENUM services
JAVA, JAIN, JSLEE, JSIP
RTP Applications, code and bits and pieces
Robustness testing
SIP and DNS information
SIP Center links pages
SIP client software
User Agents, Source Code and User Agent downloads
SIP drafts and RFCs
SIP parsers and stacks
SIP servers, proxys and gateways
Testing tools, like the SIP Test Messenger tool
Offers Development Services For