> We need to > resend in 30 seconds, perhaps, and if mumble time units elapse > without successful delivery we need to initiate a response to the > sender indicating that s/he should try another communication channel > while we continue to retry this one. Waiting 30 seconds would be unwise in the scenario described. Instead of waiting, the sending application should be sending 2 or 3 copies of the message via different routes to ensure that it gets there as quickly as possible. For existing models on how to accomplish this in IP, you should look at the financial services industry where tickers and other market datafeeds must get to the recipient as fast as possible because millions of dollars are at stake. In this environment, datafeeds are sent via multicast. Each packet is duplicated and sent via two different multicast trees which travel over infrastructure which is entirel discontiguous, i.e. separacy is enforced right down to the physical layer. It works well and something like this is likely to be the right way to handle critical emergency communications. Note that an important aspect of this type of solution is that it defeats IP routing's concept of the single best path for a packet. This means that if you don't need the multiple recipients that a market data feed requires, you might find a way to do something similar with MPLS TE that is more suited to emergency comms. > Those experts aren't in the ITU, and the ITU at this point doesn't > have the expertise to even say what was said in my long paragraph > above. And the ITU does not have applications layer experts which is what you need to design a communications solution for some very specific and very important applications layer requirements. Some people are assuming that lower level protocols need to be *fixed* to enable this but I do not agree that is the case. > I do believe that having a requirements-generating working group is a > good thing. Yes. And get some other applications domain experts to contribute such as people from the financial industry or SIAC. IMHO, the financial industry treats this matter with much greater care and importance than the defense and security sector because in the financial services industry, the impact of communications failures is immediate and can be severe. Unlike the defense and security sector who must deal with events sporadically, in financial services the events are numbered in transactions per second. --Michael Dillon _______________________________________________ Ietf@xxxxxxxx https://www1.ietf.org/mailman/listinfo/ietf