On Tue, 3 Sep 2019 at 11:09, Brandon Butterworth <[email protected]> wrote: > The expensive bit that multicast would save is dslam to peering, not > home tails, so if it was feasible this would be the ideal use case
I don't deny that a massive traffic reduction could be made from edge to content source by using multicast, that's a fundamental advantage of multicast. My qualm was that whilst Neil advocates the marvels of multicast, presumably BT has a large unicast CDN base in addition and so they are running both technologies (multicast and unicast) simultaneously. How much more advantageous was it to run multicast AND unicast simultaneously vs. putting some of that resource used to implement and maintain multicast into unicasting everything only? Would the economies of scale of going all in on unicast outweigh the benefits of investing into two technologies? > If you're paying BT 40quid/Mbit/s for backhaul and want to deliver a > 30Mb/s UHD stream to 1000 subscribers on that dslam who pay 20quid > would you like to multicast it if you could (30*40quid) or is unicast > (30*40*1000quid) fine? Have I miss-understood? In that case aren't you using the the architecture you said was dated where multicast replication happens at a few select aggregation points... > This was problem we had dating back to adsl, traffic was tunneled to > a few central aggregation points across very expensive bandwidth. > > Due the replication happening at the aggregation points the multicast > was not able save that expensive bandwidth. My query was about putting caches at the first hop of your customers; On Tue, 3 Sep 2019 at 10:03, James Bensley <[email protected]> wrote: > so in my eyes, the benefits to be had from > the reduction in traffic levels due to multicast just isn't that great > vs. the added complexity if you can plonk the content source on your > network at the 1st hop your customers hit. Sorry if it wasn't clearer, but I'm talking about something that isn't really economically possible if you're paying BT for your ADSL/VDSL backhaul. When I said 1st hop I didn't mean, you're a wholesale customer of an ADSL/VDSL provider and get traffic over an expensive NNI/L2TP session (or worse, a customer of a wholesaler ad infinitum.) and so the first hop is an LNS device half a world away from the end-site; in this case unicasting everything is a bit of a non-starter. To be clearer, I was talking from the perspective of a last mile provider (which BT are), trying to put unicast content nodes as close to the access circuit as possible (which I'm sure the do). > > I'm obviously not a fan :) > > It's technology not Taylor Swift, use what is of technical and economic > benefit. My query was on the technical and economic benefits of multicast+unicast vs. only unicast. Cheers, James.
