> Do you think any of these lower volume participants are dependent on the CQS/UQDF consolidated feeds though?

I think your probably right here, though I don't know for sure.

> I bet Bloomberg, Thompson Reuters, and co are connecting to each exchange and building their own consolidated feed rather than repackaging CQS/UQDF.

We've had both feeds and this jives with what our reps have told us. Both vendors are proud of their consolidated feed technology. And I've seen the size of one of bloomberg's tickering plants that is colo'd in Toronto. If they aren't building their own feed they have a lot of machines sitting around doing very little:)

Reuters has RDF-D which is distributed. bloomberg has B-PIPE. Both are not as good as using an overpriced FPGA (redline, nova spark, etc) and parsing the data yourself.

Yes, I think very many are dependent on these feeds. As you mentioned, they are the official prices and are referenced for compliance with all those damn regulations and most of the market relies on them so it'd be pretty much impossible to facilitate trading while it's down.

Also, trading in any derivative that is based on any underlying in the feed will be very problematic because that's where the underlying spot price come from. Options trading for example were entirely shut down in those symbols while the feed was down.

All the consolidated feeds, CTS, CQS, UTDF, UQDF are consumed for options, but they are a secondary thing and not used for pricing in real time.

Raw feeds are used. That said, Nasdaq is the most important underlier for many things in options, and that could be why some options trading stopped.

PHLX, NOM, ISE/Gemini all halted trading and all exchanges halted options trading on Nasdaq listed symbols until Nasdaq came back up at ~3:40. Yes, most sophisticated co-located firms probably use raw feeds, but how do you facilitate trading when the official feed for the underlying is down and the symbols aren't even trading on their listed exchange? (Nasdaq down from ~12 to ~3:40)