> Imagine that there is a video streaming client that takes its content stream from a combination of a multicast channel and a unicast channel. At a coarse level, the client receives packets over the multicast link and requests retransmission over the unicast. There was some very preliminary work recently presented to the (RTP) “PAYLOAD” working group describing a proposal to optimize a HTTP Adaptive Streaming video infrastructure (i.e., "HTTP Live Streaming" or “DASH”) when a live video event is carried over a multicast network. The proposal currently has lots of issues to be fleshed out, and (AFAIK) it’s still unclear whether it'll become a working group - but if you’re interested, see the thread here: https://mailarchive.ietf.org/arch/search/?email_list=payload&qdr=y&gbt=1&index=N4qSH2GcGVdMwDUNbWEdDCy5bjs Ross.