| 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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