Reliable IP-multicast protocol for large scale Bi-directional satellite communications systems

摘要

Digital content delivery service to many points via satellite communication systems has recently attracted much attention. Using an uplink circuit to check feedback messages from receivers is an effective way to enable reliable multicast transport by the retransmitting loss packets and checking delivery results. If the number of receivers is very large, a feedback implosion problem occurs. To enable reliable multicast transport to more than a few thousand receivers via satellite, Reliable IP-multicast systems for bi-directional satellite communications have been constructed. NACK-based protocol, which is an effective way to enhance system scalability, has been adapted to our system for content delivery. In our system, the sender divides the content into many data blocks to transmit-data to receivers in blocks. The sender sends a NACK-polling signal to receivers to inquire about sent blocks. The sender monitors the system for the NACK carrier. When the sender detects the carrier, the sender can judge whether to resend the data block in question based on the detection timing. The sender decides to resend the data blocks based on detecting the NACK carrier or not, instead of by analysis of demodulated NACK signal. Therefore, if NACK carriers collide, the sender can detect whether any receiver missed receiving the data block in question by detecting timing. This process enhances the scalability of the system at low cost because it enables some receivers to share an uplink circuit simultaneously. Certified test results validated our system's performance in terms of content delivery time.