The INVITE method is used to establish media sessions between User Agents. The RE-INVITE message permits the CSP to change parameters of an existing or pending call. For example, the RE-INVITE message is used with Session Timers to allow the CSP to regularly "ping" the far end to ensure that they are active.
Important! It is not possible to change the codecs (COder-DECoders) at runtime using the RE-INVITE message.
The SIP software supports the following:
• RE-INVITE messages that change the port to which media should be sent.
• RE-INVITE messages that change the connection address.
• Media stream on hold (connection address is zero).
• Initial INVITE messages on hold.
• Initial INVITE messages with no Session Description Protocol (SDP).