1. Low Delay RTCP Feedback Format

2. Low Delay RTCP Documents RTCP-based Feedback: Concepts and Message Timing Rules (draft-wenger-avt- rtcp-feedback-01.txt) Low Delay RTCP Feedback Format (draft- fukunaga-low-delay-rtcp-01.txt) –general feedback behaviour –feedback message types and formats

3. General Feedback Behaviour RTCP Compound Packets –full compound packets: SR/RR, SDES, other RTCP messages –minimal compound packets: SR/RR –full compound packets are sent according to timing rules of RTP –if feedback is to be sent in between full compound packets it is sent in minimal compound packets

4. Feedback Message Types Three Message Types (differentiated by PT-field): 1. Transport Layer Feedback Messages protocol related information RTP entity reacts directly to feedback 2. Payload Specific Feedback Messages payload or payload format specific feedback RTP entity reacts according to payload format 3. Application Layer Feedback Messages application specific information RTP entity passes the messages payload to the application as is

5. 1. Transport Layer Feedback RTP entity reacts directly to this message Examples: –General NACK indicates the loss of one or several RTP packet(s) actions of RTP entity are not specified but could include: –retransmissions –rate control –General ACK...

6. 2. Payload Specific Feedback RTP entity reacts to this message according to payload format Example: –Multiple Selective Retransmissions in RTP (draft-ietf-avt-rtp-selret-00.txt) payload format specifies syntax and semantics of feedback message RTP entity is able to do multiple selective retransmissions at receiving the feedback message which is interpreted according to the payload formats specification

7. 3. Application Layer Feedback RTP entity passes the messages payload directly to the application Examples: –NEWPRED in MPEG-4 syntax and semantics of NEWPRED messages are defined in MPEG-4 specification NEWPRED message is directly given to the MPEG-4 entity at the sender MPEG-4 entity is able to identify the message and can react –H.263/Annex N and U

8. Open Points / Discussion Structure of documents –general feedback behaviour Compound RTCP packets –possibility to send low-delay-feedback information without SR/RR Message Types –flexible enough for future uses?...