Re: [rtcweb] Lower-overhead protocol variations
Stefan Håkansson LK <stefan.lk.hakansson@ericsson.com> Mon, 25 February 2013 12:57 UTC
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Date: Mon, 25 Feb 2013 13:57:40 +0100
From: Stefan Håkansson LK <stefan.lk.hakansson@ericsson.com>
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References: <512540A3.3090008@jesup.org> <0DB30A45-97A6-4974-9CBB-BEE6691EFCE2@lurchi.franken.de> <51263522.1030206@jesup.org> <3FAF754D-8040-49FC-B0AD-F17BF705F62C@lurchi.franken.de> <512B58F2.3020408@alvestrand.no>
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Subject: Re: [rtcweb] Lower-overhead protocol variations
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On 2013-02-25 13:28, Harald Alvestrand wrote: > On 02/21/2013 09:19 PM, Michael Tuexen wrote: >> On Feb 21, 2013, at 3:54 PM, Randell Jesup wrote: >> >>> On 2/21/2013 8:03 AM, Michael Tuexen wrote: >>>> On Feb 20, 2013, at 10:31 PM, Randell Jesup wrote: >>>> >>>>> This is a relevant thread to current discussions: >>>>> http://www.w3.org/mid/D1737092-F63D-4821-B3FA-D425267E4F23@cisco.com >>>>> and continued with subject change in >>>>> http://www.w3.org/mid/4F4D6315.9000601@jesup.org >>>>> >>>>> I'm re-evaluating if the original decision against even/odd was >>>>> required, >>>>> in order to see if we can collapse the current draft 0-RTT proposal >>>>> into a single declarative "open" message on a stream with no >>>>> response or ack >>>>> required. Even/odd (perhaps based on a property of the SCTP >>>>> association?) >>>>> would avoid the need for mismatched channel pairs, and thus avoid >>>>> the need >>>>> for the response/ack and the need to send with the in-order bit. >>>> I'm not sure what you mean you even/odd? >>>> >>>> I guess you will send the "open" message reliable and ordered. OK. >>>> Are you proposing that there is no ACK sent back? What would happen >>>> if one side sends an "open" message indicating an unordered data >>>> channel, >>>> sends a user message on this channel and the user message is delivered >>>> first? >>> As you infer below, this would be one side uses even channels to >>> initiate, the other uses odd (to avoid glare). >>> The reliability question is important; the simplest solution would be >>> to buffer any data that arrives without an Open message until the >>> Open message is received, and then deliver it. There's no issue in >>> the other direction, as once the open message is received the >>> receiver can then send on that stream/channel with no restrictions. I >>> assume there's some way to reliably choose roles for even/odd >>> selection in SCTP? If not, we can find other ways to do it (even SDP >>> if we had to), though I think we could also key off the DTLS. >> Not sure we can choose based on SCTP. The port numbers can be the same >> and we have no addresses >> available. Maybe we can use the client/server identity from DTLS (the >> DTLS client uses even, >> the DTLS server uses odd). > > The MMUSIC SCTP draft (draft-ietf-mmusic-sctp-sdp-03.txt) says: > > 6. The Setup and Connection Attributes and Association Management > > The use of the 'setup' and 'connection' attributes in the context of > an SCTP association is identical to the use of these attributes in > the context of a TCP connection. That is, SCTP endpoints MUST follow > the rules in Sections 4 and 5 of RFC 4145 [RFC4145] when it comes to > the use of the 'setup' and 'connection' attributes in offer/answer > [RFC3264] exchanges. > > The relevant table from section 4 of RFC 4145 is: > > Offer Answer > ________________ > active passive / holdconn > passive active / holdconn > actpass active / passive / holdconn > holdconn holdconn > > I think that based on RFC 4145, it would be reasonable to say that the > party in the "active" role uses the even channels and the party in the > "passive" role uses the odd channels, and that if the initiator uses > "actpass", no channel assignment can be made until the answer comes back > as either "active" or "passive". > > This, of course, implies that channel numbers are reassigned from a > blank slate if the connection goes down and is reestablished with new > values for active and passive. Probably one should say that if the > connection goes down, all channels go down too - that the data channel > system doesn't attempt to layer yet another layer of reconnection on top > of the already existing ones. I think so too. For WebSockets, you get the close event (with a reason why it was closed [1]); the app has to establish a new one. The data channels should have the same behavior IMO. [1] http://dev.w3.org/html5/websockets/#closeevent > > Harald > > > _______________________________________________ > rtcweb mailing list > rtcweb@ietf.org > https://www.ietf.org/mailman/listinfo/rtcweb
- [rtcweb] Lower-overhead protocol variations Randell Jesup
- Re: [rtcweb] Lower-overhead protocol variations Michael Tuexen
- Re: [rtcweb] Lower-overhead protocol variations Randell Jesup
- Re: [rtcweb] Lower-overhead protocol variations Michael Tuexen
- Re: [rtcweb] Lower-overhead protocol variations Harald Alvestrand
- Re: [rtcweb] Lower-overhead protocol variations Stefan Håkansson LK
- Re: [rtcweb] Lower-overhead protocol variations Randell Jesup
- Re: [rtcweb] Lower-overhead protocol variations Michael Tuexen
- Re: [rtcweb] Lower-overhead protocol variations Harald Alvestrand
- Re: [rtcweb] Lower-overhead protocol variations Michael Tuexen
- Re: [rtcweb] Lower-overhead protocol variations Salvatore Loreto
- Re: [rtcweb] Lower-overhead protocol variations Salvatore Loreto
- Re: [rtcweb] Lower-overhead protocol variations Michael Tuexen
- Re: [rtcweb] Lower-overhead protocol variations Salvatore Loreto
- Re: [rtcweb] Lower-overhead protocol variations Harald Alvestrand