I don't think Jacobson was suggesting that a really new paradigm in networking would be able to handle the robust case of broadcast data, of which unicasting is simply a subset. I find you need a little creativity to fill in some of the gaps in the later part of the talk, since he wasn't presenting a design (or really, even a complete theoretical architechture) but simply some big ideas that he thought were worth a lot more attention.
Packet switched networks are fine for realtime communication, provided there is enough bandwidth and they arn't congested. That performance degrades rather than simply shutting down and/or denying new connections is a feature, not a bug. As you point out, no existing system adequately fufills the requirements of online virtual worlds which precisely why we've spent so much time building our own. The problem is a curious mix of large quantities of mostly static data (3D models, textures) punctuated by dynamic data with high frequency changes and requirements for low latency. Throw in streaming media to the mix (voice) and it's really an architechtural nightmare when you consider the vast majority of network research has been in trying to solve each of these problems in isolation and to the exclusion of the others. The reason broadcast routing is so exciting is that we're not just trying to solve how to move the latency-sensitive high-frequency bits around, but that distributing and caching static resources (geometry, textures) is a huge part of the problem, and one that we never adequately addressed in the current/old s4 design. Indeed, moving the latency-sensitive high-frequency bits around is easy, because there isn't that much of it, and the problem was largely solved by online games ten years ago. On Wed, May 09, 2007 at 12:10:16PM -0700, dan miller wrote: > Hi -- > > I'm new to the list though I have been on IRC now & then. > > I loved Jacobson's talk but one point struck me: the introduction of a new > paradigm doesn't obviate the need for the old. Packet-switching is great > for fault-tolerance when the goal is "get this packet from here to there, no > matter what." It's actually the postal paradigm (thru wind & sleet...) > > But the old telco real-time, hard-wired point-to-point connection was > actually better suited to some things we do today over packet networks, > particularly teleconferencing. The control over latency and timing is lost > when you switch to TCP (as you VOS folks know only too well). > > A data subscription model is really just a cool technological way to > introduce the concept of publishing to the digital world in a useful way; > but it doesn't change the fact that packet-switched networks are not so > great for realtime communication. > > WRT VOS/Interreality goals, in particular avatar/object behavior (whether > scripted or resulting from user input), we have a mix of requirements that > doesn't easily fit any model I'm aware of. It's time critical, like a phone > conversation; it's point-to-many-point, like publishing; it's ephemeral, > like broadcasting; but it's not fully global, in that typically you only > care about a few objects in your virtual vicinity. Distributing this data > liberally is not an option due to bandwidth. > > The bittorrent model doesn't really wash here because of the requirement for > low latenc. I think in this case we have another animal entirely, which is > basically a secure multipoint channel cluster. The closest analogy I'm > aware of would be multi-party teleconferencing. AT&T actually does this > pretty well. > > This animal should be optimized for its intended use, and not shoe-horned > into paradigms that it doesn't really fit. It might be reasonable to take a > look at some of the ITU work in this area, such as H.323, and even the IETF > VOIP/SIP stuff that's out there. > > I'm not saying we should necessarily adopt any such standards; but it is > often worthwhile to take a good look at how similar problems have been > tackled, for better or worse. Otherwise you risk spending mucho time > reinventing various types of wheels. > > -dbm -- [ Peter Amstutz ][ [EMAIL PROTECTED] ][ [EMAIL PROTECTED] ] [Lead Programmer][Interreality Project][Virtual Reality for the Internet] [ VOS: Next Generation Internet Communication][ http://interreality.org ] [ http://interreality.org/~tetron ][ pgpkey: pgpkeys.mit.edu 18C21DF7 ]
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