ARQ which stands for Automatic Retransmission reQuest or Automatic Repeat reQuest uses a patented "Negative acknowledgement" feedback-based mechanism to let the encoder know that a packet was lost during transit to the decoder, and to send a replacement (or retransmission) packet back to the decoder.
When using the same port for ARQ as the outbound transport stream port no inbound firewall ports need to be opened in order to allow the re-request back through to the encoder.
- Intelligent & rapid re-send of data: like TCP but
- Optimised for low delay video & audio with minimised overhead
- Automatic configuration
TCP vs. ARQ
- Designed for data (web, e-mail, ftp)
- No time bounds: unsuitable for video/audio
- Limits throughput
- Requires positive ACK for all packets
- Designed for live, real-time (audio, video, etc.)
- Hard time deadlines
- Allows maximum throughput
- Only negative acknowledgements (ACKs) – minimises overhead