Re: [Dart] WGLC: draft-ietf-dart-dscp-rtp-02 - Gorry's item (2)
gorry@erg.abdn.ac.uk Fri, 22 August 2014 19:13 UTC
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Date: Fri, 22 Aug 2014 20:13:03 +0100
From: gorry@erg.abdn.ac.uk
To: "Black, David" <david.black@emc.com>
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Cc: "gorry@erg.abdn.ac.uk" <gorry@erg.abdn.ac.uk>, "Black, David" <david.black@emc.com>, "dart@ietf.org" <dart@ietf.org>
Subject: Re: [Dart] WGLC: draft-ietf-dart-dscp-rtp-02 - Gorry's item (2)
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I could live with that - it would be even nicer if we actually had a document with set of recommendations to point to - but since we don't, this seems an appropriate statement. Gorry > Here's the next to last paragraph in Section 5.3: > > SCTP [RFC4960] differs from TCP in a number of ways, including the > ability to deliver messages in an order that differs from the order > in which they were sent and support for unreliable streams. However, > SCTP performs congestion control and retransmission across the entire > association, and not on a per-stream basis. Although there may be > advantages to using multiple drop precedence across SCTP streams or > within an SCTP stream that does not use reliable ordered delivery, > there is no practical operational experience in doing so (e.g., the > SCTP sockets API [RFC6458] does not support use of more than one DSCP > for an SCTP association). As a consequence, the impacts on SCTP > protocol and implementation behavior are unknown and difficult to > predict. Hence a single PHB and DSCP should be used for all packets > in an SCTP association, independent of the number or nature of > streams in that association. Similar reasoning applies to a DCCP > connection; a single PHB and DSCP should be used because the scope of > congestion control is the connection and there is no operational > experience with using more than one PHB or DSCP. > > I propose to add the following new sentence as its own paragraph: > > Guidance on transport protocol design and implementation to provide > support for use of multiple PHBs and DSCPs in a transport connection > (e.g., DCCP) or association (e.g., SCTP) is out of scope for this > document. > > I could add examples of topics that could be addressed, but would prefer > to leave that to the actual design activity. > > Thanks, > --David > > >> -----Original Message----- >> From: Black, David >> Sent: Thursday, August 14, 2014 9:16 AM >> To: gorry@erg.abdn.ac.uk; Ruediger.Geib@telekom.de >> Cc: dart@ietf.org; Black, David >> Subject: WGLC: draft-ietf-dart-dscp-rtp-02 - Gorry's item (2) >> >> Wearing none of my hats, I would prefer to put Gorry's item (2) into a >> TSV >> (Transport Area) draft somewhere, and hence prefer the suggestion to say >> that this document does not provide that sort of guidance. >> >> > > (2) I don't know if the document's goal is also to make transport >> > > recommendations for using multiple code points - i.e., things such >> as must >> > > be robust to the network changing a DSCP; needs to independently >> verify >> > > that a particular DCSP is not being black-holed, needs to not imply >> > > relative precedence when interpreting loss or marking of packets for >> a >> > > flow using multiple DCSPs etc. ??? >> > > >> > > If these are out of scope, then maybe the document should say that >> this >> > > particular document does not provide this sort of guidance. >> >> Thanks, >> --David >> >> > -----Original Message----- >> > From: Dart [mailto:dart-bounces@ietf.org] On Behalf Of >> gorry@erg.abdn.ac.uk >> > Sent: Thursday, August 14, 2014 9:06 AM >> > To: Ruediger.Geib@telekom.de >> > Cc: gorry@erg.abdn.ac.uk; dart@ietf.org >> > Subject: Re: [Dart] WGLC: draft-ietf-dart-dscp-rtp-02 >> > >> > Thanks >> > >> > When I said "transport" I was thinking of the algorithms to be used in >> the >> > end-host to figure out what was operational and where congestion and >> delay >> > were experienced. But what you say is all an import part. I expect >> what >> > you discuss, could go into the tsvwg intercom draft. >> > >> > >> > Gorry >> > > Hi Gorry, >> > > >> > > the following text will likely appear in the next version of my >> > > diffserv-intercon draft. The more DSCPs appear in a flow which >> aren't >> > > deployed end-to-end for the corresponding PHB, the more often one of >> the >> > > scenarios will be encountered. >> > > >> > > The following scenarios start from a domain sending >> > > IP traffic using a PHB and a corresponding DSCP to an interconnected >> > > domain. The receiving domain may >> > > - Support the PHB and offer the same corresponding DSCP >> > > - Not support the PHB and use the DSCP for a different PHB >> > > - Not support the PHB and not use the DSCP >> > > - Support the PHB with a differing DSCP, and the DSCP of the >> > > sending domain is not used for another PHB >> > > - Support the PHB with a differing DSCP, and the DSCP of the >> > > sending domain is used for another PHB >> > > >> > > Another question to be answered then is how a network provider will >> treat >> > > unrecognized or unexpected DSCPs received at network boundaries. >> > > >> > > Regards, >> > > >> > > Ruediger >> > > >> > > >> > > -----Ursprüngliche Nachricht----- >> > > Von: Dart [mailto:dart-bounces@ietf.org] Im Auftrag von Gorry >> Fairhurst >> > > Gesendet: Mittwoch, 13. August 2014 22:33 >> > > An: dart@ietf.org >> > > Betreff: [Dart] WGLC: draft-ietf-dart-dscp-rtp-02 >> > > >> > > >> > > I can see good points raised on the details, instead I have some >> questions >> > > about the overall document strcuture: >> > > >> > > [snip] >> > > >> > > (2) I don't know if the document's goal is also to make transport >> > > recommendations for using multiple code points - i.e.things such as >> must >> > > be robust to the network changing a DSCP; needs to independently >> verify >> > > that a particular DCSP is not being black-holed, needs to not imply >> > > relative precedence when interpreting loss or marking of packets for >> a >> > > flow using multiple DCSPs etc. ??? >> > > >> > > If these are out of scope, then maybe the document should say that >> this >> > > particular document does not provide this sort of guidance. >> > > >> > > Gorry >> > > >> > > _______________________________________________ >> > > Dart mailing list >> > > Dart@ietf.org >> > > https://www.ietf.org/mailman/listinfo/dart >> > > >> > >> > _______________________________________________ >> > Dart mailing list >> > Dart@ietf.org >> > https://www.ietf.org/mailman/listinfo/dart >
- [Dart] WGLC: draft-ietf-dart-dscp-rtp-02 - Gorry'… Black, David
- Re: [Dart] WGLC: draft-ietf-dart-dscp-rtp-02 - Go… Black, David
- Re: [Dart] WGLC: draft-ietf-dart-dscp-rtp-02 - Go… gorry
- Re: [Dart] WGLC: draft-ietf-dart-dscp-rtp-02 - Go… Black, David
- Re: [Dart] WGLC: draft-ietf-dart-dscp-rtp-02 - Go… Harald Alvestrand