Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site down.FUN Path: utzoo!watmath!clyde!burl!ulysses!allegra!princeton!down!honey From: honey@down.FUN (code 101) Newsgroups: net.mail Subject: Re: definitions for LOCAL, DEMAND, DAILY, etc Message-ID: <422@down.FUN> Date: Thu, 17-Jan-85 13:35:17 EST Article-I.D.: down.422 Posted: Thu Jan 17 13:35:17 1985 Date-Received: Fri, 18-Jan-85 02:45:14 EST References: <700@cbosgd.UUCP> <2308@garfield.UUCP> Organization: Princeton University, EECS Lines: 63 let me respond to some of andrew droskoy's queries. i gather this is a confusing point, since so many people seem confused by it. mea culpa. in simplest terms, pathalias solves the single-source shortest paths problem in a weighted, directed graph. see aho, hopcroft and ullman for details. all pathalias wants out of life is a list of weighted edges so that it can do its thing. it yaccs a high-level language to make life a little easier (for you! for me and steve it's like pulling teeth, or scratching fingernails on a blackboard). LOCAL, DEMAND, etc. act like macros for integers (cat lex.l), not "classes of service" or whatever the common misinterpretation is. on to the misinterpretations. (but first, please glance at the man page. thank you.) I have found the definitions to be a bit incomplete. For example what do you use if you will call someone on demand, but also poll them daily? I have seen people using DAILY for this, but some value less than DEMAND would perhaps be more appropriate. if you call someone on demand, the appropriate weight is DEMAND. if someone polls you every day, use DAILY. if you call on demand *and* once a day, that's no better than calling on demand, is it? so use DEMAND. DAILY+DEMAND definitely doesn't make it, since this indicates a link that is more costly (i.e., less useful/reliable/worthwhile) than DEMAND or even DAILY. as a rule of thumb, do not mix the basic costs (see man page again) -- use HIGH and LOW for minor adjustments. Another example: We call most of our connections after midnight, but only if we have something for them - and we will call them on demand up until 8am. We have been using EVENING to express this, but I am not sure this is right. EVENING is the appropriate cost. I think the definitions could stand to be made clearer. you're probably right -- help? Since Mark's reason for posting the official definitions is presumably to get us all using the same values to describe similar situations, I think some discussion on the relation of these definitions to reality would be appropriate. the values were pulled out of thin air, played with, adjusted, adjusted, etc. until the routes started looking reasonable. i don't know a better way to describe this. perhaps the mistake was to allow arithmetic expressions in the weights, which has led to confusion (as well as providing flexibility). i abase myself for having anything to do with this and am open to suggestion. coming soon in a net.sources near you: the third iteration of pathalias. i have sworn my honor that i'll post it before dallas. peter