| | SIP server | Kamailio/SIP router | OpenSIPS |
| | www | kamailio.org/sip-router.org | opensips.org |
| | License | GPL |
| | Last release | 3.2.0 | 1.7.0 | | Operating system | Linux | Linux |
| | SIP registrar | Yes | | SIP proxy | Yes |
| | B2BUA | No | Yes |
| | Low-level transaction access | Yes | | Forking | Yes | | Modular architecture | Yes |
| | NAT traversal | Yes | Yes | | with RTPProxy, Mediaproxy | with RTPProxy, Mediaproxy |
| | Keepalive | Yes |
| | Authentication and authorization against database | MySQL, PostgreSQL, SQLLite, UnixODBC, BerkeleyDB, Oracle, text files, LDAP, RADIUS, DIAMETER | MySQL, PostgreSQL, UnixODBC, BerkeleyDB, Oracle, text files, LDAP, RADIUS, DIAMETER |
| | Signalling protocols | SIP |
| | Transport protocols | UDP, TCP, TLS, SCTP | UDP, TCP, TLS, SCTP |
| | IPv4/IPv6 | Yes/yes |
| | Administrative web GUI | Yes | Yes | | SIREMIS | OpenSIPS-CP, SerMyAdmin |
| | DNS | NAPTR, SRV, ENUM | | Multidomain | Yes | | SIMPLE (presence and IM) | Yes |
| | XCAP server | Yes | Yes | | Embeded | With OpenXCAP server | | Gateway | XMPP, MSN, SMS | XMPP, MSN, SMS | | Standardized SIP service API | CPL, SIP servlet API (with Seas) | CPL, SIP servlet API | | Other service tools | Perl, Lua, Python | Perl |
| | Media services | No | | Carrier class routing | Yes | | Load balancing | Yes | | Attack protection | Yes | | IP blacklists |
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