2.1.1.3.1.1 Receivers
The receiver MUST include the RTSP header Supported: "com.microsoft.wmdrm-nd" in its RTSP request messages to indicate to the transmitter that it supports WMDRM: Network Devices Protocol .
The receiver MUST begin the license retrieval procedure by sending a DESCRIBE request to the URL that the receiver intends to play. The entity-body of the DESCRIBE request MUST contain a license request message.
The DESCRIBE request MUST include a "Content-Type: application/vnd.ms-wmdrm-license-request" header to indicate that the body of the DESCRIBE request contains a license request message.
The DESCRIBE request SHOULD include a "Require: com.microsoft.wmdrm-nd" header to indicate that the receiver expects the transmitter to be compliant with WMDRM: Network Devices Protocol .
Unlike the registration request message, the license request message MUST NOT be Base64 encoded [RFC3548].
When the receiver receives the response to the DESCRIBE request, it MUST verify that the response indicates that the request succeeded and that the Session Description Protocol (SDP) [RFC2327] description contained in the response includes the "a=key-mgmt:wmdrm-nd" attribute.
The receiver MUST verify that the "a=key-mgmt:wmdrm-nd" SDP attribute contains a URL using the data URL scheme that is defined in RFC 2397 [RFC2397], and that the MIME type of the "data" URL is "application/vnd.ms-wmdrm-license-response". This MIME type indicates that the data URL contains a license response message.
Typically, the license response is encoded in Base64 format [RFC3548]. The data URL itself will indicate if Base64 encoding has been used. In that case, the receiver MUST apply Base64 decoding when extracting the license response message from the data URL [RFC3548].