Which of the following ways does HD terminal support to initiate peer-to-peer calls?

Which of the following must the SIP request message contain?

The MCU wall riding mode does not require the use of private protocols and can be used with terminals of different manufacturers. ()

Any SIP message consists of a starting line, a header field, and a message body, and the header domain must end with CFLF (Carriage Return Line Feed).

Response messages are used to respond to request messages that indicate the status of success or failure of a call, and different types of response states are distinguished by status codes, which contain three-digit integers, the first bit of the status code Used to define the response type, the other two digits are used to further explain the response in more detail. ( )