assigned. Sequence number: (16 bits) The sequence number is incremented for each RTP data packet sent and is to be used by the receiver to detect packet loss and to accommodate out-of-order delivery. The initial value of the sequence number should be randomized to make known-plaintext attacks on Secure Real-time Transport Protocol more difficult. Timestamp: (32 bits) Used by the receiver to play back the received samples at appropriate time and interval. When several media streams are present, the timestamps may be independent in each stream. The granularity of the timing is application specific. For example, an audio application that samples data once every 125 μs (8 kHz, a common sample rate in digital telephony) would use that value as its clock resolution. Video streams typically use a 90 kHz clock. The clock granularity is one of the details that is specified in the RTP profile for an application. SSRC: (32 bits) Synchronization source identifier uniquely identifies the source of a stream. The synchronization sources within the same RTP session will be unique. CSRC: (32 bits each, the number of entries is indicated by the CSRC count field) Contributing source IDs enumerate contributing sources to a stream which has been generated from multiple sources. Header extension: (optional, presence indicated by Extension field) The first 32-bit word contains a profile-specific identifier (16 bits) and a length specifier (16 bits) that indicates the length of the extension in 32-bit units, excluding the 32 bits of the extension header. The extension header data follows. Application design A functional multimedia application requires other protocols and standards used in conjunction with RTP. Protocols such as SIP, Jingle, RTSP, H.225 and H.245 are used for session initiation, control and termination. Other standards, such as H.264, MPEG and H.263, are used for encoding the payload data as specified by the applicable RTP profile. An RTP sender captures the multimedia data, then encodes, frames and transmits it as RTP packets with appropriate timestamps and increasing timestamps and sequence numbers. The sender sets the payload type field in accordance with connection negotiation and the RTP profile in use. The RTP receiver detects missing packets and may reorder packets. It decodes the media data in the packets according to the payload type and presents the stream to its user. Standards documents , Standard 64, RTP: A Transport Protocol for Real-Time Applications , Standard 65, RTP Profile for Audio and Video