Re: [tsvwg] I-D Action: draft-tsvwg-le-phb-00.txt
<Ruediger.Geib@telekom.de> Fri, 02 December 2016 12:31 UTC
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From: Ruediger.Geib@telekom.de
To: roland.bless@kit.edu
Thread-Topic: [tsvwg] I-D Action: draft-tsvwg-le-phb-00.txt
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Date: Fri, 02 Dec 2016 12:30:18 +0000
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Cc: tsvwg@ietf.org, draft-tsvwg-le-phb@ietf.org
Subject: Re: [tsvwg] I-D Action: draft-tsvwg-le-phb-00.txt
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Hi Roland, I support your draft and I prefer the DSCP you suggest definitely more than CS1. A couple of minor comments is given below. 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… Regards, Ruediger -----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 ----------------------- 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. ------------------------------ 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). ------------------- 2. PHB Description [RG] sw /This PHB../ The LE PHB/ twice in this sentence 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. --------------------------------------------- 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. ------------------- 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/ [RG] LE traffic MUST NOT be metered and SHOULD NOT be policed? -------------------------- 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.
- 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)