PINTs and SPIRITS - service interworking
These two IETF standards address the requirement for telephony services to interwork between the PSTN and the Internet. PINT deals with services originating from an IP network; SPIRITS deals with services originating from the PSTN.
In PINT (PSTN and Internet Interworking), PSTN network services are triggered by IP requests. A SIP Java client is embedded in a Java servlet on a web server. The SIP client then launches requests to create phone calls on the telephone network. Being a lightweight client that is embedded in many devices, SIP is the ideal choice for the IP portion of signalling. It partners with INAP on the PSTN side.
The current focus of this initiative is to allow web access to voice content and enable click-to-dial/fax services. For more information, see the Programming SIP
Programming SIP
SIP's intimate association with all things Internet establishes telephony as part of a continuum of Internet media options. Its similarities with HTTP and SMTP and its text-based format mean that SIP is familiar to web developers.
In order to develop services, programmers need APIs. There have been many advances in this area of SIP, resulting in numerous new interfaces.
CPL (Call Processing Language
This was the first API developed for SIP. Strictly speaking, it is not really an API at all, but rather an XML-based scripting language for describing and controlling call services. It is designed to be implemented on either network servers or user agent servers and is meant to be simple, extensible, easily edited by graphical clients, and independent of operating system or signalling protocol.
CPL is engineered for end-user service creation: a CPL interpreter is very lightweight and a server can easily parse and validate a CPL, guarding against malicious behaviour. It is suitable for running on a server where users may not be allowed to execute arbitrary programs, as it has no variables, loops, or ability to run external programs. It has primitives for making decisions and taking actions based on call properties, such as time of day, caller, called party etc.
The SIP-CPL draft can be found on the SIP Servlets section for further information.
For further information see:
- the JAIN website at SIP Servlets section for further information.
For further information see:
- the JAIN website at Protocol Comparison
SIP and H.323/MGCP/Megaco
A comparison between the protocols to sum up the information in this section.
| | SIP | H.323 | MGCP/Megaco | | | | | | | Philosophy | Horizontal | | Vertical | Vertical Complexity | Low | | High | High Scope | Simple | | Full | Partial Scalability | Good | | Poor | Moderate New Service Revenues | Yes | | No | No Internet Fit | Yes | | No | No SS7 Compatibility | Poor | | Poor | Good Cost | Low | | High | Moderate |