QVidium QVAM140-ARQ User Manual

Page 8

User’s Manual v.2

QVidium

QVARQ A140

Technologies, Inc.

configure this to any other valid, non-conflicting UDP port. However, if you choose to change the
ARQ request port, you must make certain the settings at the encoder and decoder match.

At the receive proxy, the ARQ error correction mechanism first buffers incoming packets in a
synchronized network de-jitter buffer that maintains a constant, configurable delay for incoming
packets. The de-jitter buffer processes RTP sequence numbers and reorders packets as
necessary to restore proper packet sequence and to buffer against erratic network delays. Its goal
is to output a smooth, consistent flow of packets with increasing sequence numbers. This output
feeds the ARQ error correction mechanism.

The ARQ unit at the receive proxy watches for gaps in RTP sequence number from the de-jitter
buffer output, and immediately sends out retransmission requests when necessary. Incoming
retransmitted ARQ packets bypass the de-jitter queue and find their correct place in the ARQ
buffer, so that by the time packet are output by the ARQ buffer, the ARQ error correction
mechanism should no longer contain any missing packets.

When the encoder and decoder are both started, the receive proxy automatically measures the
round-trip delay and packet jitter to the encoder and automatically configures ARQ for optimal
operation according to a few basic user-specified parameters, as described in Section

Note: For ARQ error correction to be enabled, you must select ARQ transport at both the encoder
or video source and this receiver proxy. The encoder/video source must be configured to allow
upstream ARQ request packets to the source. If you set the ARQ port equal to the UDP port, then
for most firewalls QVidium’s ARQ will automatically configure the firewall to allow in the upstream
ARQ requests.