What is the purpose of SIP options?

The purpose of SIP OPTIONS is to query the capabilities of a SIP entity. This message allows one SIP device to discover the features and capabilities of another device within the SIP network. When a SIP endpoint sends an OPTIONS request, it is essentially asking the recipient what methods it supports, such as whether it can handle certain types of media, codec capabilities, or advanced features like call transfer or hold. The recipient responds with an OPTIONS response that details the capabilities available, which supports interoperability and helps devices make informed decisions about establishing sessions.

The other choices focus on different aspects of SIP functionality. Managing active sessions pertains to different SIP methods like INVITE, which is used to establish or modify sessions. Establishing security protocols relates to security features such as SIP over Transport Layer Security (TLS), which ensures encrypted SIP communication but does not specifically involve querying capabilities. Monitoring network performance is outside the standard functions of SIP directly, impacting aspects like Quality of Service (QoS) but is not the primary purpose of the OPTIONS method.