Hi Bruce, thanks for your excellent explanation!
Jerry > -----Original Message----- > From: Bruce Lowekamp [mailto:[EMAIL PROTECTED] > Sent: Thursday, March 06, 2008 10:35 PM > To: Jerry Yin > Cc: 'Henry Sinnreich'; 'P2PSIP Mailing List' > Subject: Re: semi-symmetric routing protocol for reload-3? > > > > On Mar 6, 2008, at 4:18 PM, Jerry Yin wrote: > > > Hi Bruce, > > > > thanks for the response, please see the in-line comments. > > > > thanks > > Jerry > > > >> -----Original Message----- > >> From: Bruce Lowekamp [mailto:[EMAIL PROTECTED] > >> Sent: Thursday, March 06, 2008 11:17 AM > >> To: Jerry Yin > >> Cc: 'Henry Sinnreich'; 'P2PSIP Mailing List' > >> Subject: Re: semi-symmetric routing protocol for reload-3? > >> > >> > >> > >> For DHTs that can route in both directions, this could work. > >> Standard Chord can't guarantee reachability if you try to route > >> backwards, however. > >> > > > > For semi-symmetric routing, it's not necessary for the responses to > > travel > > backwards all the same peers as the requests in a reverse order. As > > long as > > the peers in the via-list are in the response path, the protocol > > should work > > for any p2p algorithm. Isn't it? > > Unfortunately, no. Unless the DHT guarantees that you can route in > both directions, you can't do things like 3c routing "toward" the > peer at the top of the via list. Well, you can do that, but that > peer won't necessarily be able to reach it. > > > > >> The other problem is with routing during overlay healing. If the > >> overlay is partitioned and peer A is trying to route a message back > >> to B through some peer C, if this message is recovering from a > >> partition, C may not be in the same partition as B, so ultimately > >> following a path through C may not lead to B, even if C appears to be > >> "closer" to B. Full symmetric (or iterative) are still the most > >> reliable routing methods for these situations. > >> > > > > This could be a problem. Unless the symmetric routing will always > > use direct > > response, it will have the same problem. > > > No, it's not a problem if you use symmetric routing. Let's say you > follow the periodic stabilization in 9.2.6.3 and repeat the initial > discovery process. If peer A discovers peer Z and routes a PING > through A to its ID, then the peer R that responds to the PING will > only be able to reply to it by routing backward along the original > path through Z. > > If the overlay you're using supports bi-directional routing, then a > semi-symmetric algorithm's approach of routing backward to Z can work > fine. But not all DHTs support that. (chord, in particular, > doesn't, although variants that guarantee bi-directional routing are > used.) > > Bruce > > _______________________________________________ P2PSIP mailing list [email protected] https://www.ietf.org/mailman/listinfo/p2psip
