802.11 is a bad example. It needs reliability because its losses aren't well-correlated with congestion.
I'm not terribly concerned about TCP having reliability when used in this context, although the stream-oriented nature of TCP is unfortunate. I don't want to go to a lot of effort adding reliability to a UDP-based protocol, because I don't think it will add much (and could hurt if done wrong). Even if the overlay link protocol does have reliability, you still need to shed load with finite-length queues (or push back) to avoid congestion collapse/infinite queues. I'm curious what literature you're thinking off that argues otherwise. Bruce On Wed, Apr 8, 2009 at 8:27 AM, Henning Schulzrinne <[email protected]> wrote: > > On Apr 8, 2009, at 6:21 AM, Bruce Lowekamp wrote: > >> One of the (if not THE) fundamental decisions that makes the Internet >> work is that reliability is end-to-end, not hop-by-hop. Hops are >> allowed to drop traffic due to congestion, and that is taken as >> implicit feedback that there is congestion in the network. > > You may want to re-read the end-to-end argument paper. You do need > end-to-end reliability to ensure reliability (since nodes in the middle can > do bad things to packets), but performance often dictates "hop-by-hop", > particularly if the "hop" is essentially the whole Internet. Since you like > to use the notion of a link layer in P2P: this is the reason why 802.11 has > link-layer reliability. By your argument, 802.11 should dispense with that. > > > >> >> >> The proposal I sent out drops traffic in two places. First, each peer >> maintains a limited queue for fragments and drops excess fragments >> (the literal analog of drops due to congestion in routers). Second, >> the overlay link protocol is only semi-reliable (which I debated >> having at all), with the assumption that on the Internet, loss is due >> to congestion. So we have two congestion signals to the peer, queue >> length and link protocol drops. > > Unfortunately, that assumption is only somewhat true, particularly with > wireless links. > > >> >> >> Congestion needs to cause load shedding in a network (overlay or not) >> or else it will collapse. Arguing that we should do extra work for >> hop-by-hop reliability makes no sense to me. > > Please consult the literature; this is a topic that has received more than > its share of real measurement work, albeit ten and twenty years ago, when > this topic was of greater practical interest. > >> >> >> Bruce >> > > _______________________________________________ P2PSIP mailing list [email protected] https://www.ietf.org/mailman/listinfo/p2psip
