Re: [RTG-DIR] (resend) Re: RtgDir review: draft-ietf-rtgwg-cl-requirement-13
Lou Berger <lberger@labn.net> Fri, 17 January 2014 18:01 UTC
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From: Lou Berger <lberger@labn.net>
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Cc: rtg-dir@ietf.org, draft-ietf-rtgwg-cl-requirement.all@tools.ietf.org, "rtg-ads@tools.ietf.org" <rtg-ads@tools.ietf.org>, rtgwg@ietf.org
Subject: Re: [RTG-DIR] (resend) Re: RtgDir review: draft-ietf-rtgwg-cl-requirement-13
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sounds like a plan! Lou On 01/17/2014 12:41 PM, Curtis Villamizar wrote: > In message <52D88F77.5020009@labn.net> > Lou Berger writes: > >> Curtis, >> I'm not sure if we're going around in circles or not, but in either >> case case I think we're getting caught up in the weeds/details. >> >> >From a high level perspective, my comments have been motivated by trying >> to ensure the requirements are unambiguous -- as documented. I think >> the text changes that have been agreed to so far (notably the use of the >> capitalized term and introduction of AMG) will help a lot. I think there >> is still one more area that is unclear, but it's also possible that >> we're arguing about text that you are planning to change. >> >> Do you have a version that captures all the changes to date that you can >> distribute (or submit, as you choose)? Perhaps looking at this version >> we'll find that the ambiguity is resolved or is sufficiently narrowed to >> not be significant. Either way, the discussion can then continue from >> the most current text. >> >> Thanks, >> Lou > > > Lou, > > I was going to suggest the same (if I understand your suggestion) - > that is that a new draft be submitted and you (and others) can review > and see if clarity has been sufficiently improved or if there are > still issues with clarity. > > If that is OK with you and compatible with this process I will make > two draft submissions back to back. One with just the OpsDir review > comments addressed and a second with your comments so far addressed. > IMHO it would be easier to discuss the clarity (or lack of) of the > wording once changes have been made particularly since there are a few > s/old/new/g terminology suggestions in the email thread. > > Curtis > > >> On 1/15/2014 7:00 PM, Curtis Villamizar wrote: >>> In message <52D02F67.9070604@labn.net> >>> Lou Berger writes: >>> >>>> Curtis, >>>> >>>> I think we have one disconnect (and corresponding related text) that we >>>> need to resolve before we can be close the discussion. See below for >>>> details.. >>>> >>>> On 1/8/2014 11:33 PM, Curtis Villamizar wrote: >>>>> Converging. But maybe one more round trip needed. >>>>> >>>>> In message <52CD9D58.4010109@labn.net> >>>>> Lou Berger writes: >>>>>> >>>> ... >>>> >>>>>>>>>> 2. Editorial: server and client layer vs upper and lower layer. >>>>>>>>>> >>>>>>>>>> The document uses server and client layer networks and LSPs and, >>>>>>>>>> sometimes interchangeably or redundantly, upper and lower layer networks >>>>>>>>>> and LSPs. I think this issue can be resolved by avoiding the term >>>>>>>>>> client/server when referring to network layers and just using the >>>>>>>>>> lower/upper terminology. The one exception to this is in the definition >>>>>>>>>> Client LSP which should simply be defined in the context of a multipath, >>>>>>>>>> i.e.: >>>>>>>>>> OLD >>>>>>>>>> A client LSP is an LSP which has been set up over a server layer. >>>>>>>>>> NEW >>>>>>>>>> A client LSP is an LSP which has been set up over Advanced Multipath. >>>>>>>>> >>>>>>>>> A client LSP can be set up over a server layer MPLS-TP LSP or any >>>>>>>>> server layer MPLS LSP or over a link layer or over a pseudowire ... or >>>>>>>>> over an advanced multipath. >>>>>>>>> >>>>>>>> >>>>>>>> Would you accept s/server layer/lower layer/g? >>>>>>> >>>>>>> The definition of server layer is not the same as the definition of >>>>>>> lower layer. See below. >>>>>>> >>>>>>>>>> I think this also means that usage of the term "Client" is limited to >>>>>>>>>> "Client LSP". >>>>>>>>> >>>>>>>>> I searched for all occurances of the word client. All occurances are >>>>>>> />> "client LSP" excexpt the phrase "client of a client LSP" and that is >>>>>>>>> used only in the following paragraph. >>>>>>>>> >>>>>>>>> The ingress and egress of a multipath may be midpoint LSRs with >>>>>>>>> respect to a given client LSP. A midpoint LSR does not participate >>>>>>>>> in the signaling of any clients of the client LSP. Therefore, in >>>>>>>>> general, multipath endpoints cannot determine requirements of clients >>>>>>>>> of a client LSP through participation in the signaling of the clients >>>>>>>>> of the client LSP. >>>>>>>>> >>>>>>>>> THe point is that "A midpoint LSR does not participate in the >>>>>>>>> signaling of any clients of the client LSP" and that non-participation >>>>>>>>> in client (or higher layer) signaling applies to any "client of a >>>>>>>>> client LSP", not just other LSP running over it. >>>>>>>>> >>>>>>>>> I then searched for all occurances of the words upper and lower and >>>>>>>>> higher. There are no occurances of "upper". >>>>>>>>> >>>>>>>>> There were a few occurances of "lower latency" and "higher latency". >>>>>>>>> Other than that, all occurances of lower and higher except one are in >>>>>>>>> the follwoing text: >>>>>>>>> >>>>>>>>> 3.2. Component Links Provided by Lower Layer Networks >>>>>>>>> >>>>>>>>> A component link may be supported by a lower layer network. For >>>>>>>>> example, the lower layer may be a circuit switched network or another >>>>>>>>> MPLS network (e.g., MPLS-TP)). The lower layer network may change >>>>>>>>> the latency (and/or other performance parameters) seen by the client >>>>>>>>> layer. Currently, there is no protocol for the lower layer network >>>>>>>>> to inform the higher layer network of a change in a performance >>>>>>>>> parameter. Communication of the latency performance parameter is a >>>>>>>>> very important requirement. Communication of other performance >>>>>>>>> parameters (e.g., delay variation) is desirable. >>>>>>>>> >>>>>>>>> FR#8 The solution SHALL specify a protocol means to allow a lower >>>>>>>>> layer server network to communicate latency to the higher layer >>>>>>>>> client network. >>>>>>>>> >>>>>>>>> The exception is this sentence: >>>>>>>>> >>>>>>>>> FR#22 The solution SHOULD support the use case where an advanced >>>>>>>>> multipath itself is a component link for a higher order advanced >>>>>>>>> multipath. For example, an advanced multipath comprised of MPLS- >>>>>>>>> TP bi-directional tunnels viewed as logical links could then be >>>>>>>>> used as a component link in yet another advanced multipath that >>>>>>>>> connects MPLS routers. >>>>>>>>> >>>>>>>>> The terms lower layer and higher layer go all the way back to the ISO >>>>>>>>> seven layer model of ancient times (1970s?, 1980s?) and maybe further >>>>>>>>> back but that is before even my time. >>>>>>>>> >>>>>>>>> I don't think this is unclear but I could add the following in >>>>>>>>> definitions: >>>>>>>>> >>>>>>>>> Higher Layers >>>>>>>>> A client layer is the one immediately above a server layer. The >>>>>>>>> client layer and all layers above that layer are higher layers. >>>>>>>>> >>>>>>>>> Lower Layers >>>>>>>>> A server layer is the later immediately below a client laer. >>>>>>>>> The server layer and all layers below are lower layers. >>>>>>>>> >>>>>>>>> Do I really need to put this in the definitions section? If yoy think >>>>>>>>> it is necessary, I will add it. >>>>>>>>> >>>>>>>> Perhaps we've talked (okay written) past each other. I was suggesting >>>>>>>> using/keeping the "higher and lower layer" terminology, not dropping it. >>>>>>>> And to use it (consistently) in place of "client and server Layer". >>>>>>> >>>>>>> I guess you missed the distinction in the definition above: >>>>>>> >>>>>>> For layer X layer Y is: >>>>>>> >>>>>>> client layer === Y = X+1 >>>>>>> server layer === Y = X-1 >>>>>>> higher layer === Y > X >>>>>>> lower layer === Y < X >>>>>>> >>>>>>> So the definition client layer is not the same as the definition of >>>>>>> higher layer. The definition of server layer is not the same as the >>>>>>> definition of lower layer. >>>>>>> >>>>>>> In some discussions we really do mean "the server layer" and not any >>>>>>> layer at any arbitrary depth below this one. >>>>>> >>>>>> I read your usage of client/server layer to be synonymous with >>>>>> higher/lower layer, i.e. -+ 1. Otherwise I'm not sure how to make sense >>>>>> of FR#8 (I think you really mean client layer not lower layer.) >>>>> >>>>> FR#8 and FR#9 are about the server layer telling the client layer >>>>> about the delays that can be expected. There is a little redundancy >>>>> here so s/ower layer server network/server network/ and >>>>> s/higher layer client network/client network/. No plans to skip >>>>> layers. >>>>> >>>> >>>> I think we need to hit the points below before this one... >>> >>> OK. >>> >>>>>> Given the current document usage, I still think it makes sense to >>>>>> eliminate the two instances of "client layer": How about the following: >>>>>> OLD >>>>>> Client LSP >>>>>> A client LSP is an LSP which has been set up over a server layer. >>>>>> In the context of this discussion, a client LSP is a LSP which >>>>>> has been set up over a multipath as opposed to an LSP >>>>>> representing the multipath itself or any LSP supporting a >>>>>> component links of that multipath. >>>>>> NEW >>>>>> Client LSP >>>>>> A client LSP is a LSP which >>>>>> has been set up over Advanced Multipath as opposed to an LSP >>>>>> representing the Advanced Multipath itself or any LSP that is >>>>>> part of an Advanced Multipath Group. >>>>> >>>>> Nope. In general, a client LSP can be set up over a plain old >>>>> Ethernet on a given hop, therefore the second definition is too >>>>> narrow with this change. >>>>> >>>> >>>> humm, you didn't have that in your OLD text. In fact, the old text >>>> reads to me that an Advanced Multipath (solution?) logically sits >>>> between a client LSP and an underlying server layer in all cases. >>> >>> The "OLD" was a quote from you and it was the original text in -13. I >>> said "Nope. ..." to your suggested change to it in this way. >>> >>> Earlier >>> (http://www.ietf.org/mail-archive/web/rtgwg/current/msg04274.html) I >>> had suggested the following change: >>> >>> I don't think this is unclear but I could add the following in >>> definitions: >>> >>> Higher Layers >>> A client layer is the one immediately above a server layer. The >>> client layer and all layers above that layer are higher layers. >>> >>> Lower Layers >>> A server layer is the later immediately below a client laer. >>> The server layer and all layers below are lower layers. >>> >>> Do I really need to put this in the definitions section? If yoy think >>> it is necessary, I will add it. >>> >>> You will find this in the quoted text above. >>> >>> The definition of client LSP does not imply that Advanced Multipath is >>> a layer. This also used lower case "multipath" which we can replace >>> with AMG. There is no LAG layer in a network in with MPLS runs over >>> Ethernet and some of the Ethernets use Link Aggregation. >>> >>>> So the model I see defined by the text has the following layers >>>> >>>> Client LSP (layer) >>>> ---------- >>>> Advanced Multipath (layer/solution/construct) >>>> ---------- >>>> Server Layer (composed of AMGs which are LSPs and/or links) >>>> >>>> Is this aligned with your intent? If not, can you explain the >>>> relationship you see for Advanced Multipath Client LSPs and Advanced >>>> Multipath AMGs? >>> >>> You imaginged this model and are trying to constrain the text to fit >>> into it.. >>> >>> Consider these examples of client layer and server layer. >>> >>> plain old rfc-4206 >>> >>> LSP-1 (PSC-0) = client of LSP-2 >>> LSP-2 (PSC-1) = server of LSP-1 >>> >>> LSP over Ethernet over PW over MPLS >>> >>> LSP-1 = client of Ethernet >>> Ethernet = server of LSP-1, client of PW >>> PW = server of Ethernet, client of LSP-2 >>> LSP-2 = server of PW >>> >>> There is then the question of whether Advanced Multipath is a layer or >>> a set of techniques that can be applied at a given layer. Example >>> potential config language: >>> >>> mple { >>> tunnel x1 { >>> type multipath { >>> component tunnel x2; >>> component tunnel x3; >>> [...] >>> component intf i1; >>> component intf i2; >>> [...] >>> } >>> [...] >>> } >>> [...] >>> } >>> >>> No distinct layer above. >>> >>> An alternate: >>> >>> mple { >>> tunnel x1 { >>> [...] >>> } >>> [...] >>> } >>> >>> interface amg1; >>> type multipath { >>> component tunnel x2; >>> component tunnel x3; >>> [...] >>> component intf i1; >>> component intf i2; >>> [...] >>> } >>> [...] >>> } >>> [...] >>> } >>> >>> In the former example, the tunnel x1 is forced to use a specific set >>> of component links and apply multipath techniques to it. >>> >>> In the latter example, if tunnel x1 happen to find that interface amg1 >>> was the lowest cost or otherwise preferred way to get to its >>> destination it makes use of amg1 and if so inherits the use of the >>> multipath techniques. >>> >>> There is no distinct multipath encapsulation at the date layer so some >>> might argue that even in the second case there is no distinct layer, >>> just a configuration convenience. >>> >>> Claiming that Advanced Multipath is of itself a layer may get us into >>> a bigger can of worms. >>> >>> For example in today's ECMP, the next hop consists of multiple >>> interfaces. ECMP is not considered a layer between IP and those >>> interfaces. Link bundle is also not considered a layer. >>> >>> In the document we have not claimed that Advanced Multipath is a type >>> of layer and we have not claimed that Advanced Multipath is not a type >>> of layer. Either way we would get someone arguing that the opposite >>> was true. [Some individuals it seems would pick the opposite of >>> whatever we picked just because they like to argue about layering.] >>> >>> Need I remind you of the painfully long and mostly pointless arguments >>> in MPLS during the early MPLS-TP work about whether an MPLS LSP >>> carried within another hierarchical MPLS LSP was a layer or a >>> sub-layer. We don't want to repeat that and the best way to do so is >>> to not make any statement about whether Advanced Multipath is a layer >>> or a sub-layer or a layering NOOP. >>> >>> Which of the above is the "right" way to do things may be at most a >>> framework issue but may not come up until management plane entities >>> are defined. It is certainly not a topic for a requirements document >>> because it is deep into the "how it gets done". >>> >>>>>> and >>>>>> OLD >>>>>> The above set of requirements apply to component links with different >>>>>> characteristics regardless as to whether those component links are >>>>>> provided by parallel physical links between nodes or provided by sets >>>>>> of paths across a network provided by server layer LSP. >>>>>> NEW >>>>>> The above set of requirements apply to component links with different >>>>>> characteristics regardless as to whether those component links are >>>>>> provided by parallel physical links between nodes or provided by >>>>>> LSPs that are part of an Advanced Multipath Group. >>>>> >>>>> What about PW? Those are paths too by the definition of paths, so >>>>> again, this change makes the definition too narrow. >>>>> >>>> >>>> PWs weren't mentioned in your OLD text, so I didn't add them. I also >>>> have no objections to adding them. >>> >>> Actually the text you wrote is incorrect. "The above requirement >>> applies to component links" can include physical links and server >>> layer LSP but adding that are part of an Advanced Multipath Group is >>> incorrect. >>> >>> I'm not sure but I think this instance of "server layer" was added to >>> that LSP wording because you were confused on last review about client >>> LSP vs LSP over which Advanced Multipath was applied so I went around >>> changing everything to "client LSP" or "server layer LSP" to make it >>> more clear to you. You now seem to be stuck on the wording that is >>> essentially saying "any type of component link" including "server >>> layer LSP". >>> >>>> The only change I made was >>>> s/sets of paths across a network provided by server layer LSP./ >>>> LSPs that are part of an Advanced Multipath Group. >>> >>> And that change was wrong. A more correct change would be >>> >>> s/provided by server layer LSP/including paths provided by server >>> layer LSP/ >>> >>> That would include any sort of path across the network. PW could be >>> considered an emulated physcial link or another usable type of path >>> across the network. >>> >>> The "above set of requirements" in this case have to do with passing >>> down requirements for min latency, bounded latency, and bounded >>> jitter. The original paragraph is: >>> >>> The above set of requirements apply to component links with >>> different characteristics regardless as to whether those component >>> links are provided by parallel physical links between nodes or >>> provided by sets of paths across a network provided by server layer >>> LSP. >>> >>> The intent is "The above set of requirements apply to component links" >>> followed by "regardless of what type of component links they are" >>> where we had disccssed two types being an interface or emulated >>> interface (or virtual interface in some major vendor terms) or an LSP >>> (which is also a virtual interface in some major vendor terms). >>> >>> I don't understand how you can get so hung up on the wording of what >>> is intended to convey "regardless of what type of component links they >>> are". This has always been clear to the WG. >>> >>>>>>> The word "indicate" is independent of the method of getting the >>>>>>> information there. But yes in the example given the IGP advertisement >>>>>>> and MPLS LSP signaling that might be one such mechanism does refer to >>>>>>> the IGP and RSVP-TE MPLS/GMPLS that we all are familiar with. >>>>>>> >>>>>>> If client and server LSP are PSC-3 and PSC-4 in MPLS hierarchy there >>>>>>> is only one IGP flooding information for both client and server layer, >>>>>>> hence the seemingly endless (and mostly pointless) discussion of >>>>>>> sub-layer vs layer from certain ITU people in the MPLS WG mailing list >>>>>>> who viewed MPLS as broken for not enforcing a strict layering in this >>>>>>> regard. But we need not go into that level of detail in this example >>>>>>> of how independent of mechanism the "indicate" is and down that years >>>>>>> old MPLS WG terminology rat hole again. >>>>>>> >>>>>> My comment is that you need to be clear to which layer a requirement >>>>>> applies. Is it the server layer, the client layer or the Advanced >>>>>> Multipath layer? >>>>> >>>>> In each of the requirements you cited it is very clear that the client >>>>> later is communicating a requirement to the server layer, but if you'd >>>>> like I can reword to make that even more clear by rewording of the >>>>> form "SHALL provide a means for the client layer to indicate the >>>>> requirements of a client LSP [regarding X]", where X is minimize >>>>> latency (FR#10), bound latency (FR#11), bound jitter (FR#12), specific >>>>> component link (FR#13), bidirection co-routed (FR#14), no reordering >>>>> (FR#15), bounded frequency of rebalance (FR#20). >>>> >>>> Okay, I think this will/may help. My comment goes back to the model I >>>> was asking about above. And to which part of the puzzle the requirement >>>> applies. >>> >>> In some of the above requirements client layer communicated to the >>> server layer, whatever the server layer is. Means of communication >>> presumed to be RSVP-TE but we can't say that until the framework and >>> same capability needs to be available to management plane. >>> >>> In some of the above requirements server layer communicates to the >>> client layer. Means of communication is presumed to be IGP >>> extensions, again with same capability available to management plane. >>> >>> There is no distinct Advanced Multipath layer in control plane or data >>> plane. And if there was a distinct control plane layer it would be >>> defined in a framework, not a requirements document. >>> >>>>>>>>> It would be trivial to make this FR#1 and renumber the rest. >>>>>>>>> >>>>>>>> >>>>>>>> I don't think the FR helped clarify the above question. >>>>>>> >>>>>>> The choice of the word "indicate" in FR10-13, FR14, FR15 does not >>>>>>> imply usage by a specific layer. That is a direct answer to your >>>>>>> question. >>>>>>> >>>>>>> In all of these specific cases, the the client layer is passing a >>>>>>> requirement to the server layer so in the IGP + RSVP-TE world that >>>>>>> would be a function of RSVP-TE. In the absense of control plane, it >>>>>>> would have to be done through management plane interaction where the >>>>>>> client indicates requirements of an LSP and the server layer is free >>>>>>> to figure out how to meet those requirements. >>>>>>> >>>>>>> Do you want me to add the clarification on the use of the word >>>>>>> "indicate" or not? >>>>>> >>>>>> I think you need to be clear that the requirement applies to all three >>>>>> layers. >>>>> >>>>> There are no distinct three layers. You are imagining a model that is >>>>> not used in this document so please don't impose model on our document. >>>>> >>>> >>>> Well your old definition of Client LSP said that it was a client of >>>> "multipath" and else where you say that "multipath" operates over a >>>> server layer. As mentioned above, this sounds like three layers to me. >>>> If this is not your intent, I think you need to make it clear (through >>>> revised text) what model you do intend. >>> >>> This is the current text in -13: >>> >>> Client LSP >>> A client LSP is an LSP which has been set up over a server layer. >>> In the context of this discussion, a client LSP is a LSP which >>> has been set up over a multipath as opposed to an LSP >>> representing the multipath itself or any LSP supporting a >>> component links of that multipath. >>> >>> The text is trying to clarify what a "client LSP" is in the first >>> sentence and then trying to give two cases of what a client LSP is >>> not. This clarification was specifically added *for you* in the last >>> iteration. >>> >>> There was no intention to imply that Advanced Multipath is or is not >>> in of itself a type of layer. If you are getting that notion from >>> this text, then we need to change it. >>> >>> OLD: >>> >>> Client LSP >>> A client LSP is an LSP which has been set up over a server layer. >>> In the context of this discussion, a client LSP is a LSP which >>> has been set up over a multipath as opposed to an LSP >>> representing the multipath itself or any LSP supporting a >>> component links of that multipath. >>> >>> NEW: >>> >>> Client LSP >>> >>> A client LSP is an LSP which has been set up over a set of one >>> or more lower layers. In the context of this discussion, one >>> type of client LSP is a LSP which has been set up over an AMG. >>> >>> We could also add a clarification to the definitions section that >>> states: >>> >>> This document makes no statement on whether Advanced Multipath is >>> itself a layer or whether an instance of AMG is itself a layer. >>> This is to avoid engaging in long and pointless discussions about >>> what consistitutes a proper layer. >>> >>> I would *really* like to add the above statement. >>> >>>>> In your sentence above I have no idea what "the requirement" refers to. >>>>> >>>>> In summary: >>>>> >>>>> We were discussing why the word "indicate" was used to avoid requiring >>>>> specific mechanisms for information passing and I asked if I should >>>>> add the following. >>>>> >>>>> FR#0 In requirements that follow in this document the word >>>>> "indicate" is used where information may be provided by either >>>>> the combination of link state IGP advertisement and MPLS LSP >>>>> signaling or via management plane protocols. In later documents >>>>> providing framework and protocol definitions both signaling and >>>>> management plane mechanisms MUST be defined. >>>>> >>>>> Information is two way. The requirements you cited were all worded in >>>>> the form "The solution SHALL provide a means to indicate that a client >>>>> LSP will ...". So far I have offerred to reword this to the form "The >>>>> solution SHALL provide a means for the client layer to indicate a >>>>> requirement that a client LSP will ..." (ie: get minimum latency, get >>>>> bound latency, etc). >>>>> >>>>> Is adding FR#0 OK? >>>>> >>>>> Do you want this sort of rewording to make it more explicit that the >>>>> client layer is communication a requirement for a specific client LSP? >>>>> >>>> >>>> I think we need to come back to this once we resolve the "model" topic. >>>> >>>> ... >>>> >>>> Thanks, >>>> Lou >>> >>> I hope it is resolved. >>> >>> Curtis >
- Re: [RTG-DIR] (resend) Re: RtgDir review: draft-i… Lou Berger
- [RTG-DIR] RtgDir review: draft-ietf-rtgwg-cl-requ… Lou Berger
- Re: [RTG-DIR] (resend) Re: RtgDir review: draft-i… Curtis Villamizar
- Re: [RTG-DIR] RtgDir review: draft-ietf-rtgwg-cl-… Curtis Villamizar
- [RTG-DIR] (resend) Re: RtgDir review: draft-ietf-… Curtis Villamizar
- Re: [RTG-DIR] (resend) Re: RtgDir review: draft-i… Lou Berger
- Re: [RTG-DIR] (resend) Re: RtgDir review: draft-i… Curtis Villamizar
- Re: [RTG-DIR] (resend) Re: RtgDir review: draft-i… Lou Berger
- Re: [RTG-DIR] (resend) Re: RtgDir review: draft-i… Curtis Villamizar
- Re: [RTG-DIR] (resend) Re: RtgDir review: draft-i… Lou Berger
- Re: [RTG-DIR] (resend) Re: RtgDir review: draft-i… Curtis Villamizar
- Re: [RTG-DIR] (resend) Re: RtgDir review: draft-i… Lou Berger
- Re: [RTG-DIR] (resend) Re: RtgDir review: draft-i… Curtis Villamizar
- Re: [RTG-DIR] (resend) Re: RtgDir review: draft-i… Lou Berger