Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!munnari.oz.au!mundamutti.cs.mu.OZ.AU!kre From: kre@cs.mu.OZ.AU (Robert Elz) Newsgroups: comp.protocols.appletalk Subject: Re: Phase 1 vs. Phase 2 Message-ID: Date: 19 Jan 91 09:21:29 GMT References: <1991Jan17.205340.11378@pbs.org> <1991Jan18.175928.11397@pbs.org> <48271@apple.Apple.COM> Sender: news@cs.mu.oz.au Lines: 67 hayes@Apple.COM (Jim Hayes) writes: >Of course LocalTalk (which is Phase I) has not changed This isn't quite right, LocalTalk is Phase 2 too if it contains only Phase 2 routers, look closely at the RTMP packets and you will see the difference. But its "non-extended" Phase 2, which means you have the hassle of it being Phase 2 (all your routers on it have to change), and you get none of the benefits at all... Hosts connected to localtalk (especially those with their network code in ROM) don't have to change at all - this is the real cause of the lack of enhancement of localtalk. >The Phase II routers are responsible for keeping track of zone names. Routers (Phase 1 or 2) have always done that >The Mac's only care about the zone they appear to be in and the nearest >router. I think this is the question that was really being asked (which your footnote partially answered) ... if you have multiple zones on a net, the "zone they are in" isn't so simple any more, a mac can't simply ask a router "Hey! what's my zone?" Instead, the mac asks the router "What zones do you have?" and then gives its user (assuming it has one) a list of zones to pick from. That becomes the mac's zone. (For "mac" here, read "appletalk client", it need not be a mac). The mac then remembers that zone, and doesn't ask any more as long as it remains a legal zone on the net. The user can switch zones more or less whenever he likes (some servers running on the mac may not cope all that well). For devices without users to query, and which aren't configured, there is a "default" zone that the device will end up using. >If there were many routers on a backbone and only two >handled a particular zone, only those two would be bothered when folks >ask about that zone. This isn't right - if you have a backbone (ie: net), all the routers on it contain the exact same list of zones for that net (or your configuration is badly broken). Of those routers, only one is "bothered" to handle lookups (one of them receives the request and re-broadcasts it) in either phase 1 or phase 2. However, if you have many hosts on your net (including all the routers in their role as hosts), and only two of the hosts are in a particular zone, then (usually) only those two will be bothered by the lookup packet being broadcast (multicast). Its "usually" because a hash function is onvolved, and its possible that two zones might hash into the same value. >Note, however, that a zone name cannot be "disjoint" through routers. This is simple nonsense. >Specifically, if you have three nets separated by routers and they're >all in the No Parking zone, you can't create an additional Zone on each >end without it also appearing in the middle. Yes you can. kre