Effect of RTCP bandwidth on feedback delay

摘要

With the evolution of high-speed networks, many problems related to insufficient and width are being solved. This paper shows by using some additional bandwidth as provided in high- speed networks, it is possible to increase feedback frequency in a session. The real-time transport protocol (RTP) provides end-to-end transport functions suitable for real-time multimedia applications. RTP's real time control protocol (RTCP) is based on periodic multicast transmission of control packets to all session members. It provides traffic monitoring by gathering certain control statistics and sending them as feedback on the quality of data distribution. It is also used by adaptive applications to reduce network congestion. The feedback should be sent periodically within acceptable time intervals. In a large session, this is not the case as feedback is sent rarely. This happens because, according to the current RTCP specifications, all RTCP reports multicast to all members must not consume more than a small fraction (nominally 5%) of the whole bandwidth assigned for the session. Consequently, RTCP reporting interval grows with session size resulting in infrequent feedback in large sessions. The experience of users during short intervals is not utilised and hence the feedback reports do not provide timely and useful information. We conducted two sets of simulations. The first set shows the increase of feedback delay in a large session due to limiting RTCP band-width. The second set shows that by allowing RTCP more bandwidth, the average number of feedback reports is increased in all sessions providing better and timely feedback.