Path: utzoo!utgpu!watserv1!watmath!att!pacbell.com!ucsd!orion.oac.uci.edu!ucivax!gateway From: ala@lucid.COM ("Alyson L. Abramowitz") Newsgroups: comp.protocols.iso.x400 Subject: Ports in Abstract Protocol specs Message-ID: <9012102016.AA01659@atlantis> Date: 10 Dec 90 20:24:55 GMT References: , <554118*JPALME@QZ.qz.se> Lines: 53 Approved: usenet@ICS.UCI.EDU Autoforwarded: true Date: Mon, 10 Dec 1990 16:20:52 +0100 From: Jacob Palme QZ Subject: Ports in Abstract Protocol specs To: ISO/CCITT Group Communication , mhsnews@uninett.no, eu-mhsnews@uninett.no Mmdf-Warning: Parse error in original version of preceding line at ICS.UCI.EDU Autoforwarded: true I am a little confused on the usage of ports in abstract protocol specifications. Why is the communication between two agents split into different ports? What is the advantage? Is this purely an abstract notation, or does it mean that if a UA wants to connect to more than one port on a Service Agent, then multiple connections have to be opened. If the latter, why is this an advantage? A port is totally an abstract notation which can be a useful mechanism both for modeling and for conformance. In general, however, it has really not been used for much in X.400 and (particularly) X.500. At the end of the last Study Period there was a suggestion to get rid of the ports from X.500 (I can't remember if we wanted to make it all one port or just get rid of them entirely). It came down to not being worth the fight for a purely documentation issue. So that is why there is a statement in X.500 about ports not being related to conformance. One advantage with ports might be do make access control easier, if only some UA-s can access some ports which provide some kind of privileged access. But if this is the reason for organizaing the protocol into ports, then why has X.500 different ports for search and retrieval? Yes, that has been a suggestion. Group some operations together and put them as one level of access and others (say administrative operations) as another level of access. Another philosophy suggests that this is really an interface issue and all you need to do is provide a different user interface where priviledged copmmands/operations are not available and that ports aren't necessary to accomplish this. X.500's ports were done before conformance was considered. They were grouped by similar function rather than anything else as I remember. At this point the ports are purely historical and should not be taken as having any inner meaning. Can the same operation occur via more than one port? Sure. Hope this helps explain one of the more obscure parts of OSI. Best, Alyson