Hi DCCPers, In Montreal, we had a discussion about what service codes should be used by apps using DTLS over DCCP. The discussion was inconclusive, and we decided to continue it on the list, so let's do it :-).
Remember that the Service Code is a field in DCCP-Request packets that "Describes the application-level service to which the client application wants to connect." (from RFC4340). This is complicated because we're moving from a world where apps are identified by ports to a world where they're identified by service codes -- and just what do ports mean in this world?. Well-known ports are useful; they allow you to connect without some sort of extra lookup. But if you have a well-known port for an app there's going to be the tendency to identify it by that. And what's the difference between a well-known port and a well-known service code? Why do we have ports? Personally, my view is that service codes should identify apps, and ports allow you to run multiple instances of an app on a server or client. Then there's the question of whether App A running over DCCP is different from App A running over DTLS/DCCP. My conclusion is that they are different, because the app over DTLS/DCCP can offer more services/functions (confidentiality and authentication) than the app over just DCCP (unless these functions were built directly into the app, and then why bother with DTLS?). HTTP and HTTPS (and SIP and SIPS) use different URIs because they offer different services -- similar, sure, but different in some details. I would expect apps that use DCCP to similarly offer different URIs for DTLS or not. So given that, here's some proposed text as a straw man: "An application using DTLS over DCCP MUST register a new service code for the combination." Tom P.
