Asterisk is a widely used free and open-source PBX software solution employed by numerous individuals, enterprises, and businesses worldwide. It proves to be a highly equipped and affordable choice for businesses of varying sizes.

OpenSIPS, or open sip server, serves as a free and open-source proxy server designed for handling video, voice, IM, presence, and other SIP extensions. It operates as a multipurpose and multi-functional SIP signaling server, functioning as a SIP Registrar, Switch/Router, Application Server, Load Balancer, Session Border Controller, SIP Front end, Nat traversal server, and more.

Both Asterisk and OpenSIPS fall under the category of free and open-source projects designed for Voice over Internet Protocol (VoIP). Despite their shared purpose, they exhibit differences in functionality, strengths, and weaknesses.

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Architecture Difference:

The architecture of the asterisk is complex and is based on the Back 2 Back User Agent(B2BUA) style. It is responsible for signaling and for media transmission. It is also used to handle services such as protocol translation(SIP, IAX2), codec translation(uLaw, G.729a), Interactive Voice Response(IVR), voicemail, and call distribution TTS, and voice recognition, etc.

On the other hand, architecture of the structure of OpenSIPS is very simple as compare to Asterisk. OpenSIPS is a SIP Proxy is only deal with signaling.

Connectivity Difference

Asterisk provides many telephony interface cards to connect the PSTN such as DAHDI. Installation and configuration of telephony cards in Asterisk are very easy.

On the other hand, you cannot install a telephony card in OpenSIPS. OpenSIPS required an external SIP gateway to connect the PSTN.

Load Balancing Difference

By using Asterisk load balance can be configured via callid, username, and URI and also handle failover.

A unique feature of OpenSIPS is that it uses hashing algorithms for load balancing and can be configured to load balance by the username, Ruri, callid. OpenSIPS failover awareness can make for a very complementary part of an Asterisk solution.

Access Difference

Asterisk provides low-level access to protocol and makes alerts the header signal. Asterisk provides only access to IAX protocol and transfer signal in the same port and in the same packet.

OpenSIPS like asterisk provide low-level access to protocol and make alter the header signal. But in OpenSIPS it is possible to translate two incompatible versions of sip and directly handles the SIP response, header and request.

No Integration Difference

Both Asterisk and OpenSIPS have built-in integration with Radius, LDAP, and Diameter.

Media Services Difference

Asterisk is capable to provide media-related services like voicemail, voice recognition, IVR and TTS, etc. openSIPs on the other hand cannot provide media-related services like voicemail, voice recognition, IVR and TTS, etc.