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Abstract
Session Initiation Protocol (SIP) is an internet signaling protocol, developed by the IETF (starting in 1996), for establishing, maintaining, and tearing down sessions between a variety of real-time media, including voice, video, and chat. SIP allows endpoints to locate other endpoints, whether stationary or mobile. SIP doesn't have to worry about transporting voice or video as Real Time Transport Protocol (RTP) takes care of that. It also relies on Session Description Protocol (SDP) to negotiate capabilities and codecs. SIP does not provide a Directory Service or Authentication, but it does work with services such as LDAP or RADIUS. SIP is only concerned with signaling. This white paper is going to look at the way SIP is used in the converged Unified Communications environment.
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Introduction
What is this hot topic you keep hearing so much about? To keep it simple, Session Initiation Protocol (SIP) is an internet signaling protocol, developed by the Internet Engineering Task Force (IETF), starting in 1996, for establishing, maintaining, and tearing down sessions between a variety of real-time media, including voice, video, and chat. SIP allows endpoints to locate other endpoints, whether stationary or mobile. SIP doesn't have to worry about transporting voice or video as Real Time Transport Protocol (RTP) takes care of that. It also relies on Session Description Protocol (SDP) to negotiate capabilities and codecs. SIP does not provide a directory service or authentication, but it does work with services such as LDAP or RADIUS. SIP is only concerned with signaling. This white paper looks at the way SIP is used in the converged Unified Communications environment.
SIP: What Is It Good For?
What can we use SIP for? The list is long and growing with the massive acceptance of the protocol. A few things currently using SIP are voice calls, web page click-to-dial, voice messaging, instant messaging, home automation, and interactive gaming. SIP is everywhere. In fact you may be using it without realizing it. SIP is the premier call control and signaling protocol for IP communication.
SIP plays a role with client applications such as SIP Users Agents in the SIP endpoints, network applications realized by SIP servers such as Registration Servers, Presence Servers, and IM servers to name a few, and distributed network applications in collaboration with enterprise and Service Providers. Evolving communication networks must meet business imperatives to reduce cost and improve the customer experience; user imperatives that enhance the user experience and guarantee their acceptance; and IT imperatives requiring flexible applications to accommodate changing business models and that allow for centralized configuration and administration while addressing security requirements. SIP can be implemented into an existing infrastructure or be the foundation of a new network infrastructure.
The key for enterprises will be to have a roadmap that guides them toward a fully SIP-based architecture while eliminating the need to rip and replace. While this "all SIP environment" for both wired and wireless endpoints and trunks is the eventual goal, it is essential that organizations be able to leverage existing investments and move toward that objective in a fashion that meets their budgetary requirements.
The Benefits of SIP
• SIP is indifferent to the media content it carries. This opens support for a variety of communication possibilities, e.g., video, voice, instant message (IM), etc., sessions.
• It uses an Address of Record (AOR), a single unifying public address for that user that links the user to all compatible devices:one phone number that can find you anywhere.
• It supports access to the PSTN as it ports the PSTN number to the SIP Media Gateway.
• SIP is based on Internet Protocols HTTP and SMTP, using the same messaging format and header structure, making it easily integrated with other Internet services and applications. It is text-based so it is easy to read