Re: [rtcweb] JSEP: Why always offer actpass?
Stefan Håkansson LK <stefan.lk.hakansson@ericsson.com> Sun, 30 November 2014 15:26 UTC
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From: Stefan Håkansson LK <stefan.lk.hakansson@ericsson.com>
To: "Makaraju, Maridi Raju (Raju)" <Raju.Makaraju@alcatel-lucent.com>, Christer Holmberg <christer.holmberg@ericsson.com>, Roman Shpount <roman@telurix.com>
Thread-Topic: [rtcweb] JSEP: Why always offer actpass?
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Date: Sun, 30 Nov 2014 15:26:45 +0000
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Subject: Re: [rtcweb] JSEP: Why always offer actpass?
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On 30/11/14 16:06, Makaraju, Maridi Raju (Raju) wrote: >> On 30/11/14 14:51, Makaraju, Maridi Raju (Raju) wrote: >>>> Hi, >>>> >>>>>> RFC 7345 (UDPTL-DTLS) says the following: >>>>>> >>>>>> "Once an offer/answer exchange has been completed, either >>>>>> endpoint >>>> MAY >>>>>> send a new offer in order to modify the session. The >>>>>> endpoints >>>> can >>>>>> reuse the existing DTLS association if the key fingerprint >>>>>> values >>>> and >>>>>> transport parameters indicated by each endpoint are unchanged. >>>>>> Otherwise, following the rules for the initial offer/answer >>>> exchange, >>>>>> the endpoints can negotiate and create a new DTLS association >>>>>> and, once created, delete the previous DTLS association, >>>>>> following the same rules for the initial offer/answer exchange. >>>>>> Each endpoint needs to be prepared to receive data on both the >>>>>> new and old DTLS associations as long as both are alive." >>>>>> >>>>>> So, I guess that can be read in a way that the setup attribute >>>>>> as such >>>> does not impact previously >>>>>> negotiated TLS roles - unless the key fingerprint values and/or >>>>>> transport >>>> parameters are modified. >>>>>> >>>>>> The SCTP-SDP draft currently says that a subsequent offer must >>>>>> not change >>>> the previously negotiated roles. But, I guess >>>>>> we could say something similar as in RFC 7345. >>>>> >>>>> I have struggled with this language quite a bit from the >>>>> implementation >>>> perspective. I think we need to explicitly state >>>>> that endpoints MUST reuse the existing association if the key >>>>> fingerprint >>>> values and transport parameters indicated >>>>> by each endpoint are unchanged. >>>> >>>> We could take such general approach. >>>> >>>> However, for 'SCTP/DTLS' (DTLS over SCTP), I assume that the DTLS >>>> connection will also be re-established if the underlying SCTP >>>> association is re- established - even if no transport parameters >>>> etc are changed. >>>> >>>> Also, RFC 6083 says: >>>> >>>> "Each DTLS connection MUST be established and terminated within the >>>> same SCTP association." >>>> >>>> >>>>> The way this language reads to me is that endpoints can reuse the >>>>> existing >>>> association if they want to, but they can create a new one if they >>>> don't. Also, when this new >>>>> association is created, it is unclear if old setup roles MUST be >>>>> preserved >>>> or if they MUST be selected based on the current offer/answer >>>> exchange. It seems the current >>>>> specification language is not strong or clear enough on this >>>>> topic. >>>> >>>> In my opinion, IF a new DTLS connection needs to be established >>>> (for whatever reasons), the current roles should be used. >>> >>> <Raju> When ICE is NOT used, how does the offerer know that the >>> answerer does not change the fingerprint and/or transport parameters? >>> I guess it does not know. So, offerer has to be prepared for new DTLS >>> association by offering actpass. When ICE is used, the answerer can't >>> change transport parameter unless offerer does ICE restart (which >>> changes offerer transport parameters); Ref [1] is very clear on this >>> indicating "DTLS handshake procedure is repeated". However, even when >>> ICE is used, I do not find any restriction about answerer not >>> changing fingerprint. So, even without ICE restart answerer can >>> trigger a DTLS renegotiation by changing its fingerprint. >>> >>> To conclude all this, IMO whether ICE is used or not, sending actpass >>> for all new offers may be cover all possible scenarios. >> >> That is also my conclusion based on the discussion so far. >> >> I also think the JSEP draft as far as detailed out is correct, but info >> about how the implementation should behave for Subsequent answers is >> missing. Text saying that the role must be maintained (unless there is >> an ICE restart) should be put in there. > > <Raju> > Hi Stefan, > Looks like, there is some misunderstanding here. Probably my fault in that case :) > My conclusion is to include > actpass, but not the previously negotiated role, in all subsequent offers, > not just during ICE-restarts. I think that is what the JSEP draft says - and my conclusion is that it _is_ correct. My point was that the _answer_ should (when it is a subsequent answer) should say the same role as in previous answers (unless there is an ICE restart). > This is to handle the scenario of answerer changing fingerprint, which > is allowed (i.e. not explicitly disallowed), in a more > natural way by renegotiating the roles. Entity which wants to change fingerprint > may also want to renegotiate the role even when transport parameters are not changed. > > Also, when ICE is not used answerer can change transport parameters which needs > renegotiation of roles. > > So, to have uniform rules for ICE (restart or not) and no ICE it is better to > send the role in subsequent offer as if it is an initial offer (i.e. actpass). That is also my understanding (and what the JSEP draft says). > </Raju> > > BR > Raju > >
- [rtcweb] JSEP: Why always offer actpass? Stefan Håkansson LK
- Re: [rtcweb] JSEP: Why always offer actpass? Justin Uberti
- Re: [rtcweb] JSEP: Why always offer actpass? Stefan Håkansson LK
- Re: [rtcweb] JSEP: Why always offer actpass? Makaraju, Maridi Raju (Raju)
- Re: [rtcweb] JSEP: Why always offer actpass? Stefan Håkansson LK
- Re: [rtcweb] JSEP: Why always offer actpass? Makaraju, Maridi Raju (Raju)
- Re: [rtcweb] JSEP: Why always offer actpass? Stefan Håkansson LK
- Re: [rtcweb] JSEP: Why always offer actpass? Roman Shpount
- Re: [rtcweb] JSEP: Why always offer actpass? Makaraju, Maridi Raju (Raju)
- Re: [rtcweb] JSEP: Why always offer actpass? Christer Holmberg
- Re: [rtcweb] JSEP: Why always offer actpass? Roman Shpount
- Re: [rtcweb] JSEP: Why always offer actpass? Christer Holmberg
- Re: [rtcweb] JSEP: Why always offer actpass? Makaraju, Maridi Raju (Raju)
- Re: [rtcweb] JSEP: Why always offer actpass? Stefan Håkansson LK
- Re: [rtcweb] JSEP: Why always offer actpass? Makaraju, Maridi Raju (Raju)
- Re: [rtcweb] JSEP: Why always offer actpass? Stefan Håkansson LK
- Re: [rtcweb] JSEP: Why always offer actpass? Christer Holmberg
- Re: [rtcweb] JSEP: Why always offer actpass? Makaraju, Maridi Raju (Raju)
- Re: [rtcweb] JSEP: Why always offer actpass? Justin Uberti
- Re: [rtcweb] JSEP: Why always offer actpass? Stefan Håkansson LK
- Re: [rtcweb] JSEP: Why always offer actpass? Christer Holmberg
- Re: [rtcweb] JSEP: Why always offer actpass? Justin Uberti
- Re: [rtcweb] JSEP: Why always offer actpass? Christer Holmberg
- Re: [rtcweb] JSEP: Why always offer actpass? Justin Uberti
- Re: [rtcweb] JSEP: Why always offer actpass? Christer Holmberg
- Re: [rtcweb] JSEP: Why always offer actpass? Christer Holmberg
- Re: [rtcweb] JSEP: Why always offer actpass? Stefan Håkansson LK
- Re: [rtcweb] JSEP: Why always offer actpass? Christer Holmberg
- Re: [rtcweb] JSEP: Why always offer actpass? Stefan Håkansson LK
- Re: [rtcweb] JSEP: Why always offer actpass? Makaraju, Maridi Raju (Raju)
- Re: [rtcweb] JSEP: Why always offer actpass? Christer Holmberg
- Re: [rtcweb] JSEP: Why always offer actpass? Justin Uberti
- Re: [rtcweb] JSEP: Why always offer actpass? Christer Holmberg
- Re: [rtcweb] JSEP: Why always offer actpass? Makaraju, Maridi Raju (Raju)