# SIP Realm

A SIP realm is a [SIP](/glossary/s/sip) authentication/authorization component, defining the set of usernames and passwords for a particular protection domain. The SIP realm does not have to be the same as a the [SIP domain](/glossary/s/sip_domain).

The SIP Realm is used together with an [SIP authentication username](/glossary/s/sip_auth) to provide access to SIP services.