Hi Dan, Thanks for the detail in this and your previous message. I agree that this is worthwhile to explore for the next version of dccp-natencap and it'll give me a good head start on working things out. Tom P. > -----Original Message----- > From: Dan Wing [mailto:dwing@xxxxxxxxx] > Sent: Saturday, February 23, 2008 1:03 PM > To: gorry@xxxxxxxxxxxxxx > Cc: Phelan, Tom; 'Colin Perkins'; ''dccp' working group' > Subject: RE: DCCP-over-UDP [was draft-phelan-dccp-natencap-00.txt] > > > Can you explain why 100ms seems reasonable? > > Longer than that would become noticable in those cases where DCCP-RAW was > being blocked. > > > I commonly use paths that have much longer delays than this, > > and would > > have expected native DCCP/IP encapsulation to still be used in these > > cases, rather than defaulting to an encapsulated format. > > The algorithm I am proposing would still achieve that. The algorithm I am > proposing has you send a DCCP-RAW request and wait 100ms for a response. > If > no DCCP-RAW response is received in that 100ms, you then try DCCP-UDP. > You do > _not_ abandon the DCCP-RAW connection attempt, however. This will provide > you > with a DCCP-RAW connection even over >100ms round-trip delay paths. I > agree > that if the first DCCP-RAW request is dropped (due to network congestion > or > other reasons) you may, for that connection, end up with DCCP-UDP > (assuming > the DCCP-UDP request and its response are not dropped). I don't see a > solution to that problem, other than waiting a really long time for the > DCCP-RAW to fail. Waiting a really long time for DCCP-RAW to fail will > make > DCCP-UDP seem very slow at connection establishment, and I will cause > DCCP-UDP > connection setup to be perceived as 'slow' by users and user applications. > > > > The case with no middlebox (NAT or firewall): > > > > DCCP client DNS server DCCP server > ----------- ---------- ----------- > | | | > |---- DNS SRV?----------------->| | > |---- DNS A?------------------->| | > |<--- DNS SRV ------------------| | > (not used)|<--- DNS A - ------------------| | > |----------------------- DCCP-RAW request----->| > (wait 100ms) > |----------------------- DCCP-UDP request ---->| > |<--- DCCP-RAW response -----------------------| > (continue with DCCP-RAW connection) > |<--- DCCP-UDP response -----------------------| > (this DCCP-UDP response isn't needed, so abort it) > |----------------------- DCCP-UDP close ------>| > | | | > > with a middlebox: > > DCCP client middlebox DNS server DCCP server > ----------- --------- ---------- ----------- > | | | | > |---- DNS SRV?----------------->| | > |---- DNS A?------------------->| | > |<--- DNS SRV ------------------| | > (not used)|<--- DNS A - ------------------| | > |---------------X | | > (wait 100ms) | | | > |----------------------- DCCP-UDP request ---->| > |<--- DCCP-UDP response -----------------------| > (continue with DCCP-UDP connection) | | > | | | | > > -d
