Understanding OpenSIPS

OpenSIPS is an open source, GPLed, multipurpose SIP server that is able to perform a large set of SIP-related functions, such as SIP Registrar, SIP proxy/router, Instant Messaging server, Presence server, SIP Redirect server, SIP load balancer or SIP Dispatcher, SIP Back-to-Back user agent, Call Queuing System, SIP IP gateway, SIP media controller, SIP application server, and many others.

OpenSIPS defines itself via the following three major capabilities:

• Performance: It is translated into a huge throughput actively measured up to 60,000 calls per second, 1.5 million simultaneous calls, 5 million registered users, and 1 million TCP connections, all in a single OpenSIPS instance running on a mid-level server
• Feature-rich: It is translated into more than 160 modules providing functionalities or features related to the SIP protocol, SQL or NoSQL DB operations, AAA integrations, routing algorithms (quality, prefix, load-based routing, and dial plans), management and control (events and external commands), and many others
• Flexibility: It is provided by the routing language; a simple but powerful scripting language (shell-like) that allows you to program OpenSIPS to handle the SIP traffic in the way you want

OpenSIPS as a SIP server is mainly about processing and handling the SIP traffic. OpenSIPS does not have media capabilities (handling RTP) at all. Nevertheless, there are external extensions that can be used to enable OpenSIPS not to handle but to control the RTP traffic, such as controlling external media relays (RTPproxy, MediaProxy, and RTPEngine) or external transcoders (Sangoma D1 transcoding cards).

There are two words that describe OpenSIPS perfectly—SIP and Engine:

• OpenSIPS is designed for SIP: From this perspective, OpenSIPS covers the providing of various transport protocol for SIP (UDP, TCP, TLS, SCTP, WebSockets, and so on) and also implementing an RFC-compliant SIP stack to handle the SIP packet (parsing, building, and changing).
• OpenSIPS means handling and processing: OpenSIPS has a powerful but flexible engine able to handle the SIP traffic in the most efficient, fast, and customized way. Any kind of routing logic can be implemented with the OpenSIPS processing engine.

The capabilities and throughput of OpenSIPS simply makes it the core entity of any SIP platform; whatever the service type is, whatever the size is, and whatever the requirements are.