Learn More. ExtraHop Reveal x All Resources. Protocol Support Library. What is SIP? VoIP is a family of technologies that all support sending or receiving voice messages over the internet.
SIP is an application protocol used to carry all forms of digital media, including voice messages—so SIP is a specific technology that supports VoIP calls. The "session," however, is not a maintained connection as many enterprises have come to think of sessions.
This means that it can work in and between IPv4 and IPv6 models. Exactly what does SIP do? SIP does this by providing five different functions:. SIP determines user locations by a registration process. When a soft-phone is activated on a laptop, it sends out a registration to the SIP server announcing availability to the communications network.
Voice over-IP VoIP phones, cellular phones, or even complete teleconferencing systems can be registered as well. Depending on the registration point chosen, there may be several different locations registered simultaneously.
User availability is simply a method of determining whether or not a user would be willing to answer a request to communicate. If you "call" and no one answers, SIP determines that a user is not available. A user can have several locations registered, but might only accept incoming communications on one device. If that is not answered, it transfers to another device, or transfers the call to another application, such as voicemail. With all the various different methods and standards of multimedia communications, something is needed to check for compatibility between the communications and the users' capabilities.
For example, if a user has an IP phone on their desk, a white-board conference via that device would not work. SIP establishes the session parameter for both ends of the communications — more specifically, where one person calls and the other answers. This function provides the greatest amount of user awe. Provided a device is capable, a user could transfer from one device to another — such as from an IP-based phone to a laptop — without causing a noticeable impact.
A user's overall capabilities would change — such as being able to start new applications such as white-board sharing — perhaps affecting the voice quality temporarily as SIP re-evaluates and modifies the communications streams to return the voice quality.
With SIP session management, a user can also change a session by making it a conference call, changing a telephone call to a video conference, or opening an in-house developed application. And finally, SIP terminates the communications.
The uses for such sessions include voice, video, chat and instant messaging, as well as interactive games and virtual reality. SIP can be used to control Internet multimedia conferences, Internet telephone calls and multimedia distribution, in both the core and the periphery of the communications network. To address the requirements of carrier-grade equipment manufacturers for SIP protocol software with high reliability, performance and scalability, Metaswitch has developed DC-SIP, a robust, high-function, flexible and portable SIP software implementation.
Skip to Content. A Microsoft Company. SIP invitations are used to create sessions and carry session descriptions that allow participants to agree on a set of compatible media types.
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