dtm@MBUNIX.MITRE.ORG (04/20/89)
I'm interested in information regarding the use of Precedence in the IP Type of Service field. The draft Host Requirements document (April 6 ver.) states the following: "The Precedence field is intended for Department of Defense applications of the Internet Protocols, and is outside the scope of this document and the IP standard specification. Vendors should consult the Defense Communications Agency (DCA) for guidance on the IP Precedence field and its implications for other protocol layers." I'm not aware of any implementations using Precedence. Does anyone have information regarding present or future use of the Precedence field? Also, if anyone knows of the appropriate people in DCA to contact, I would appreciate the information. Thanx in advance. David Miller MITRE Corporation dtm@mbunix.mitre.org
Mills@UDEL.EDU (04/22/89)
David, So far as I know, the only IP implementation to use the precedence field in the forwarding function is the Fuzzzball, which led a brief but flashy life as the switching engine in the NSFNET Phase-I backbone network prior to July 1988. These gizmos used the precedence field as a priority indicator in a conventional FB(n) queue service discipline. However, and this has not been widely known, if the precedence field was zero, which is what almost all implmentations (except the Fuzzball) used, the priority indicator was taken as the type-of-service bits read as a three-bit number. If even those bits were zero and either the source or destination TCP port field was 23 (TELNET), then the priority indicator was assumed as one. You will note that (a) if the precedence/TOS field was zero, TELNET won; (b) if the delay or throughput bits were set, they won over (a); (c) if a nonzero precedence was set, they won over (b); and (c) Fuzzballs themselves used a precedence field of all ones, so they always won. Oh yes, TELNET usually won, but FTP usually lost. All this in the bad old days of horrendous congestion when desperate men were driven to desparate measures. Surely these crimes of history will never haunt us again, at least for the next month or two. Further culpa of mea can be found in my papers in the SIGCOMM 87 and SIGCOMM 88 proceedings. I surely would not admit that above nonsense in a rag like that. And, oh yes, the Fuzzballs are still around. Have you read your clock lately? Dave
barns@GATEWAY.MITRE.ORG (Bill Barns) (04/24/89)
David, The text to which you refer, and similar material in several other places, amounts to HR WG hand-waving to disclaim responsibility for the subject. As for the DCA side, I could mention a few things, but it might lead into topics best reserved to a less widely distributed forum. How about giving me a call sometime at (703) 883-6832 and we'll talk about the whole area; or, send me email and tell me more about the context of your interest and I'll try to come up with appropriate material. Bill Barns / MITRE-Washington Networking Center / barns@gateway.mitre.org