SIP (Session Initiation Protocol) is a “signaling” system for connecting, monitoring and disconnecting connections across the internet. A SIP Trunk is a network interface device that recognizes SIP signals and can process these signals to other SIP devices. SIP Trunking is provided by a Softswitch or SBC-Session Border Controller which provides, among other things, signal processing, protocol conversion, transcoding conversion, call routing, QoS-Quality of Service, AAA-Authorization, Authentication and Accounting functions as well as switching control interface to and from gateways.

What is SIP Trunking Really? (technical)

Used For?

For internet conferencing, telephony, presence, events notification (emergency calling) and instant messaging. SIP has also been expanded to support video and instant-messaging applications. The function of signaling is to connect, monitor, alter and disconnect communications sessions. If you prefer, establish, change and terminate sessions. SIP does not address message content. SIP also uses a series of signaling commands to provide common responses.

How Does SIP Operate?

SIP is a telephony signaling protocol that is used to establish a “communications session or connection” such as a telephone call, IM-Instant Message, conference call or other type of communications on an IP-Internet Protocol network. SIP is a request-response protocol that operates like a “communications browser” protocol such as HTTP-Hypertext Transfer Protocol. SIP is the communications equivalent to such internet protocols such as HTTP and SMTP-Simple Mail Transfer Protocol (SMTP).

Uses a text-based programming language designed to perform basic call-control tasks, such as session call set up and tear down as well as signaling for features such as call hold, caller ID, conferencing and call transferring.

Flexible Design

SIP is an OSI Model Layer 5-Session protocol and is Layer 4-Transport protocol independent. SIP can be used with any Transport Layer-4 protocol such as:

  • UDP-User Datagram Protocol used in connection less communications such as streaming) and
  • TCP-Transmission Control Protocol used in connection-oriented verified transmission data transactions. SIP works on any other lower Layer 3 and below protocol such as IP-Internet Protocol, Ethernet, Frame Relay, and ATM-Asynchronous Transfer Mode.