Re: [tsvwg] I-D Action: draft-tsvwg-le-phb-00.txt
"Bless, Roland (TM)" <roland.bless@kit.edu> Mon, 06 February 2017 11:52 UTC
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To: Ruediger.Geib@telekom.de
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From: "Bless, Roland (TM)" <roland.bless@kit.edu>
Organization: Institute of Telematics, Karlsruhe Institute of Technology
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Subject: Re: [tsvwg] I-D Action: draft-tsvwg-le-phb-00.txt
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Hi Rüdiger, thanks for the comments. I just submitted a new version of the draft and tried to incorporate most of your comments. Comments inline. Am 02.12.2016 um 13:30 schrieb Ruediger.Geib@telekom.de: > I observe that the text as is contains two “SHOULD”. I think to > recall statements of either WG chairs or ADs that a low number of > “SHOULD” and the absence “MUST” standards language is insufficient to > justify standards track. Maybe David or Gorry could add a statement > whether my recollections reflects an individual point of view rather > than IETF policy. > > This is to say, I RECOMMEND to add some more standards language… :-) I tried to do that. However, since DiffServ is quite flexibly defined (w.r.t. internal marking and PHB mapping), I wasn't able to identify many places for MUSTs. > -----Comments-------------- > > 1. Introduction > > intended for traffic of sufficiently low urgency > > traffic has got a low priority in time, which does not necessarily > imply that it is generally of minor importance > > traffic for which delivery is considered optional. > > 1.1. Applicability > > for sending extremely non-critical traffic > > [RG] the above definitions of traffic suitable for LE transport may > be harmonized. I'm not sure whether 'does not imply minor importance' > and 'extremely non-critical' match each other really well. Maybe: > The PHB LE is applicable for traffic and applications of a user > accepting the presence of severe congestion conditions during any > time an LE marked IP flow is sent. > > [RG] See also RFC 4594 (whose definition may be an option here too): > Low-Priority Data for applications or services that can tolerate > short or long interruptions of packet flows. The Low-Priority Data > service class can be viewed as "don't care" to some degree I tried to harmonize this now, please check the new version. > ----------------------- > > OLD: This is a PHB that allows networks to protect themselves from > selected types of traffic rather than giving a selected traffic > aggregate preferential treatment. Moreover, it may also exploit all > unused resources from other PHBs NEW: The LE PHB allows networks to > protect themselves from selected types of traffic rather than giving > a selected traffic aggregate preferential treatment. Moreover, the > LE PHB may also exploit all unused resources from other PHBs > > [RG] I'd suggest to explicitly mention LE in that section. Done. > ------------------------------ > > 1.2. Deployment Considerations > > No harm to other traffic: since the LE PHB has got the lowest > priority it does not take resources from other PHBs. Deployment > across different provider domains causes no trust issues or attack > vectors to existing traffic. o No parameters or configuration: the > LE PHB requires no parameters and no configuration of traffic > profiles and so on. > > [RG] Please state whether this a deployment example. This should > clarify whether the described deployment is intended to be normative > (is a 'lowest priority [queue]' the only way to deploy the LE PHB? I > don't think so). Tried to make this more clear in the section. > ------------------- > > 2. PHB Description > > [RG] sw /This PHB../ The LE PHB/ twice in this sentence Done. > A packet forwarded with this PHB SHOULD have lower precedence than > packets forwarded with the default PHB. Ideally, LE packets should > be forwarded only if no best-effort packet is waiting for its > transmission. A straightforward implementation could be a simple > priority scheduler serving the default PHB queue with higher > priority than the lower-effort PHB queue. Alternative > implementations may use scheduling algorithms that assign a very > small weight to the LE class. This, however, may sometimes cause > better service for LE packets compared to BE packets in cases when > the BE share is fully utilized and the LE share not. > > [RG] I'm not sure, whether (precedence? applies (but I'm not a native > speaker). May be a generic description of the properties should be > added or replace this section: In the case of congestion, LE marked > traffic SHOULD (MUST?) be dropped prior to dropping any default PHB > traffic (my take). This leaves space for queuing LE traffic, if > desired. If the statement is should be dropped immediately in case of > congestion of the default PHB (i.e. no queuing), I'm fine with that > too. > > [RG] Related to the original text, please note that the BE traffic > will consume any spare LE bandwidth. During congestion, both will > compete for spare bandwidth of other classes by their weight and will > consume their minimum guaranteed bandwidth. Your original text > doesn't mention congestion as a pre-condition for LE traffic getting > better performance than BE traffic. Tried to incorporate these comments. > --------------------------------------------- 3. Traffic > Conditioning Actions As for most other PHBs an initial classification > and marking would usually be performed at the first DS boundary node. > In many cases, packets may also be pre-marked in DS aware end systems > by applications due to their specific knowledge about the particular > precedence of packets. There is no incentive for DS domains to > distrust this initial marking, because letting LE traffic enter a DS > domain causes no harm. > > [RG] I'd prefer the conditioning section to express a requirement of > explicit user consent to LE transport in any part of his > communication. Maybe: - SHOULD be pre-marked as LE by DS aware user > terminals originating traffic - MAY be classified an marked LE by > User managed devices within the user domain - Default PHB traffic > MUST NOT be classified and remarked to LE by a DS boundary node which > isn't managed by a user. I used the alternative phrases: If possible, packets SHOULD be pre-marked in DS-aware end systems by applications due to their specific knowledge about the particular precedence of packets. Non-LE traffic (e.g., BE traffic) SHOULD not be remarked to LE on a regular basis without consent or knowledge of the user. > ------------------- > > Usually, the amount of LE traffic is implicitly limited by queueing > mechanisms and related discard actions of the PHB. Therefore, there > is normally no need to meter and police LE traffic explicitly. > > [RG] sw /queueing/queuing/ Not sure, RFC2474 also uses queueing. RFC editor will let me know :-) > [RG] LE traffic MUST NOT be metered and SHOULD NOT be policed? I think this statement would be too strong. Assume that someone wants to forward LE, but hasn't got any LE queue left, so it must be mapped to the BE PHB. I order to make sure that it doesn't adversely affect the BE aggregate, one could use a token bucket policer at the ingress to limit the LE bandwidth. I don't want to preclude that, though the disadvantage compared to the queue solution it quite obvious. > -------------------------- > > 4. Recommended DS Codepoint > > [RG] sw /The recommended/The RECOMMENDED/ > > RFC 4594 [RFC4594] recommended to use CS1 as codepoint (as mentioned > in [RFC3662]. > > [RG] RFC4594 in a way also adds information related to LE marking if > a domain doesn’t support LE. I’d suggest to add a Diffserv-intercon > discussion here. Suggested text: > > [RG] It is further suggested that a sending domain internally marking > LE traffic by CS1 remarks traffic by the LE DSCP 000 010 recommended > above, if it is forwarded to a domain applying Diffserv-intercon and > its treatment of CS1 marked traffic is unknown. This raises the > probability that the DSCP is preserved end-to-end, whereas as CS1 > marked packet may be remarked by the default DSCP by the receiving > domain. > > [RG] Extract of RFC 4594: In network segments that use IP precedence > marking, only one of the two service classes can be supported, > High-Throughput Data or Low-Priority Data. We RECOMMEND that the > DSCP value(s) of the unsupported service class be changed to 000xx1 > on ingress and changed back to original value(s) on egress of the > network segment that uses precedence marking. For example, if > Low-Priority Data is mapped to Standard service class, then 000001 > DSCP marking MAY be used to distinguish it from Standard marked > packets on egress. Thanks for pointing that out. I now added the following text: o [RFC4594] recommended to remark Low-Priority Data to DSCP '000001' inside a DS domain that uses IP precedence marking. By using the herein defined LE DSCP such remarking is not necessary, so even if Low-Priority Data is unsupported (i.e., mapped to the default PHB) the LE DSCP should be kept across the domain as RECOMMENDED in Section 5. Regards, Roland
- Re: [tsvwg] I-D Action: draft-tsvwg-le-phb-00.txt Brian E Carpenter
- Re: [tsvwg] I-D Action: draft-tsvwg-le-phb-00.txt Ruediger.Geib
- Re: [tsvwg] I-D Action: draft-tsvwg-le-phb-00.txt Bless, Roland (TM)