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
