Re: [alto] Chair review of path-vector-13 (Part 2 of 2) Mon, 22 February 2021 15:35 UTC

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Subject: Re: [alto] Chair review of path-vector-13 (Part 2 of 2)
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Hi Vijay and the ALTO WG,

This is a follow-up on the issues that are not fully address in the previous email. Please see inline. A full text is also attached as a reference.




-----Original Messages-----
From:"Vijay Gurbani" <>
Sent Time:2021-02-11 00:23:13 (Thursday)
Cc: "IETF ALTO" <>
Subject: [alto] Chair review of path-vector-13 (Part 2 of 2)

Dear Authors: This part concludes my chair review of path-vector, an important ALTO extension.  Thank you for your work on this document.  I hope the comments in this part and the first part help position the document better.

Chair review from Section 7 to the end of the document.
Part 2 of 2.

Global comment: Please turn all "Content-Length: [TBD]" into "Content-Length: XXX", where "XXX" is the computed content length.

[PV] All the "[TBD]" are now replaced with the actual content length value.


- S7.1.3: When you first get into JSON object declarations, you should point the reader to S8.2 of RFC7285, where the semantics related to the syntax used to declare ALTO JSON objects is defined.  This will help new implementers who
pick up this manuscript and need to understand where the declaration syntax, and previously declared JSON ALTO objects, like ReqFilteredCostMap, reside.

- S8.3: I think the ALTO response deserves a longer explanation here.  Let me see if I understand correctly: the cost map returns two properties: NET1 and AGGR.  On NET1, the max reservable bandwidth is 50 Gb (or GB?), i.e., inside the NET1 abstraction of Figure 5, the max reservable bandwidth is much higher than the link bandwidth.  For the AGGR (BTW, what does AGGR stand for?  Minimum aggregate bandwidth?), the max reservable bandwidth is 10 Gbps, which is the bandwidth of L1.  Yes?  Please expand the explanation in the document to be as explicit as you can.

Further, my suggestion would be to show the NET1 and AGGR from source to destination, because that will necessarily include traversing two links, L1 and L2.  What would be the AGGR there?

- S9.2: I am not sure what the prescription here is.  Whatever it is, it needs to be (a) explicit, and (b) stronger.  Current text says that this document does not "specify" the use of path vector cost type with RFC 8189.  Why does it not specify this?  Is it because such integration is not possible?  In which case, the document should say so.  Or is it because the authors have not studied whether such integration makes sense and can be supported in a backward compatible manner?  If so, well, say so.  Or is it because such integration is not possible at all?  If so, say so.  This is a protocol document, we need to be as unambiguous as possible.  (S9.3 is a good example of drawing a line in the sand.)  

- S10.2: Not sure why the MAY is normative here.  This paragraph should be re-written in its entirety; it reads more like a draft set of notes than something well thought out.

- S11, last paragraph: I am not sure what "intolerable increment of the server-side storage" means here.  Isn't the issue more along the lines of spending CPU cycles doing path computation rather than storage requirements? Conflating "storage" here does not seem to be warranted, but perhaps I am mistaken.  Please advise.

Further, the text says, "To avoid this risk, authenticity and authorization of this ALTO service may need to be better protected." ==> I am unsure how this helps.  The ALTO server has no means to authenticate the client, nor does it have any means to know whether the client is authorized to send it a request.  Consequently, the best it can do to protect itself is to monitor client behaviour and stop accepting requests if the client misbehaves (sends same requests frequently, sends requests with small deltas frequently, or it can ask the client to solve some puzzle before submitting a request, etc.).  But generally, this class of resource exhaustion attacks are hard to defend against, and I am not sure that we will come up with something that is definitely prescriptive here.  But we should structure the discussion such that it appears that we have thought of the issues here.


- S7.1.6, bullet item "The Unified Property Map part MUST also include "Resource-Id" and "Content-Type" in its header." ==> Doesn't the unified-props I-D already mandate this?  If so, why repeat it here?

- S9: I would suggest changing the title to "Compatibility with other ALTO extensions"

- S10.1, paragraph 3: I would suggest the following re-write for this paragraph:

"In practice, developing a bespoke language for general-purpose boolean tests can be a complex undertaking, and it is conceivable that there are some existing implementations already (the authors have not done an exhaustive search to determine whether there are such implementations).  One avenue to develop such a language may be to explore extending current query languages like XQuery or JSONiq and integrating these with ALTO."

(Please provide references for XQuery and JSONiq.)


- S8.1: s/The example ALTO server provides/Assume that an ALTO server provides/

- S9.1: s/conducting any incompatibility./incurring any incompatibility problems./

- S11: s/requires additional considerations/requires additional scrutiny/

-S11: s/authenticity and authorization/authentication and authorization/

Thank you!