Some of the features that OpenSER brings:

• robust and performant SIP (RFC3261) Registrar server, Location server, Proxy server and Redirect server
• small footprint - the binary file is small size, functionality can be stripped/added via modules
• plug&play module interface - ability to add new extensions, without touching the core, therefore assuring a great stability of core components
• stateless and transactional statefull SIP Proxy processing
• support for UDP/TCP/TLS transport layers
• IPv4 and IPv6
  
• support for SRV and NAPTR DNS
• SRV DNS failover
• IP Blacklists
  
• multi-homed (mhomed) and multi-domain support
  
• scripting language for configurations file. With a syntax similar to sripting languages, the configuration offers a powerful and flexible way to deploy custom SIP services.
• management interface via FIFO file and unix sockets
• pseudo-variables to access and manage parts of the SIP messages and attributes specific to users and server
• authentication, authorization and accounting (AAA) via database (MySQL, Postgress, text files), RADIUS and DIAMETER
• digest and IP authentication
  
• CPL - Call Processing Language (RFC3880)
• SNMP - interface to Simple Network Management Protocol
• XMLRPC -management interface via XMLRPC
  
• NAT traversal support for SIP and RTP traffic
• ENUM support
• PERL Programming Interface - embed your extensions written in Perl
• Java SIP Servlet Application Interface - write Java SIP Servlets to extent your VoIP services and integrate with web services
  
• load balancing with failover
  
• least cost routing
• support for replication - REGISTER offer new functions for replicating client information (real source and received socket).
• logging capabilities - can log custom messages including any header or pseudo-variable and parts of SIP message structure.
• modular architecture - plug-and-play module interface to extend the server's functionality
• gateway to sms or xmpp
• multiple database backends - MySQL, PostgreSQL, flat files and other database types which have unixodbc drivers
• straightforward interconnection with PSTN gateways
  
• impressive extension repository - over 70 modules are included in OpenSER repository
  

Scalability:

• OpenSER can run on embedded systems, with limitted resources - the performances can be up to hundreds of call setups per second
• used a load balancer in stateless mode, OpenSER can handle over 5000 call setups per second
• on systems with 4GB memory, OpenSER can serve a population over 300 000 online subscribers
• system can easily scale by adding more OpenSER servers
• OpenSER can be used in geographic distributed VoIP platforms
• straightforward failover and redundancy

New features in OpenSER 1.2.0

New features in OpenSER 1.1.0

New features in OpenSER 1.0.1

News in OpenSER 0.9.4 vs. SER 0.9.0

OpenSER History