An Internet standard specified by the Internet Engineering Task Force (IETF) in RFC 2543. SIP is used to initiate, manage, and terminate interactive sessions between one or more users on the Internet. SIP, which borrows heavily from HTTP and the e-mail protocol SMTP, provides scalability, extensibility, and flexibility, and capabilities for creating new services. SIP is increasingly used for Internet telephony signaling, in gateways, PC phones, softswitches, and softphones, but it is not limited to Internet telephony, and can be used to initiate and manage any type of session, including video, interactive games, and text chat.