Introduction and Uses of Sip UK
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The Session Initiation Protocol (SIP) is a signaling protocol, developed for Internet telephony. It moves away from the old idea of having to call a user before you can communicate with them and now allows users to join a call rather than having to be called first.
SIP has become popular because of its flexibility, and it is now widely used in voice-over-IP communications, as well as instant messaging. It also allows the creation of both open-source PBX systems and private enterprise IP telephony solutions that are reliable, easy to configure, and require little network bandwidth.
SIP was originally designed by Mark Handley, Henning Schulz Rinne, Eve Schooler, and Jonathan Rosenberg in 1996. In November 2000, SIP was accepted as a 3GPP signaling protocol and is now used for Internet multimedia communications such as voice and video calls, chat, and instant messaging.
SIP gained popularity after it was submitted as an IETF proposed standard in 1999. SIP has now become the leading signaling protocol for Voice over IP, replacing H.323-based gatekeepers
SIP is used by many VoIP systems; Google's Gmail uses SIP to communicate with other email servers, Skype uses it to connect to their backend servers and Comcast Cablevision uses it to connect their cable boxes. It is also used by IMS systems integrated with SIP
Protocol operation of Sip
SIP is only involved in the signaling operation of the endpoints; it does not carry any media data. SIP allows both IPv4 and IPv6 addresses to be used, but if IPv6 is used then IPsec must be supported.
SIP UK is designed to run over UDP which ensures it's easy to use, but without TCP SIP responds faster during congestion and also degrades well. This lightweight approach makes the protocol well suited for both server and embedded devices
If calling between private networks running SIP you can use either IPV4 or IPV6. If calling via the public internet you must use IPV4 because IPv6 is not supported
SIP uses TCP for reliable transport of call signaling messages only. This means that any SIP device can run on a computer without an operating system, which allows embedded devices to implement SIP protocol using software alone
Network elements of Sip UK
The network elements that use SIP are the User Agent Client (UAC) and the User Agent Server (UAS). The UAC is responsible for creating SIP requests and sending them to the UAS which responds with a SIP response.
Network elements of Sip are:
User-agent: A user agent is a logical network endpoint that generates the requests and responses in the protocol. A user agent is usually implemented by a client application, but can also be implemented on either or both ends of a logical connection by either the calling or called party.
Proxy server: A proxy server is a network server with UAC and UAS capabilities. It often resides at the edge of a network and routes requests to other SIP entities. It is also able to authenticate and authorize user requests.
Redirect server: A redirect server is a user agent server that responds to requests with a 3xx response and includes a contact address.
SIP Registrar: A registrar is a user agent server that can also accept REGISTER requests. SIP registrars are logical elements that provide a mapping between SIP users and the SIP URI (Uniform Resource Identifier) where they can be reached.
Gateway: A user agent server that has UAC capabilities but does not implement anything other than routing functionality. The gateway usually translates signaling messages into different protocol formats; for example, converting SIP requests to ISUP (ISDN User Part) for PSTN systems.
What is SIP used for?
SIP is used to signal and control interactive user sessions that may involve multimedia elements such as video, voice, instant messaging, online games, or virtual reality. SIP is frequently used to set up and tear down calls between telephone numbers.
SIP can also be used for some automated services such as video conferencing which is often more complicated than making a phone call because of the way the content is programmed.
The main use for SIP right now is in VoIP (Voice over IP) which enables a person to make a phone call without needing a traditional telephone or cellphone, all that's needed is an internet connection and a SIP-enabled device such as the Jaja Spot A10 home Phone Adapter.
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