[alto] Comments on draft-ietf-alto-new-transport-08

["maqiufang (A)" <[e-mail]>]

Hi, all

Notice that Jordi was asking for volunteers to review ALTO WG documents, I tried to spend some time reviewing this ALTO new transport document and my comments are following.
Note that some of my questions/comments may be due to my not fully understanding of this document(sorry!)...

Sec.1 Introduction
Specifically, this document specifies the
   following:

   *  Extensions to the ALTO Protocol to create, update, or remove an
      incrementally changing network information resource.
So I thought that the ALTO client can request to create and delete a TIPS view, and also query the content of the TIPS or receive push updates. But I am not sure how the ALTO protocol could be extended to allow the client to update that view. I thought ALTO is a network information exposure protocol, the capability to update a network information resource sounds surprising to me.


Sec.2.1 Transport Requirements
s/direct/directly

Sec.2.2 TIPS Terminology

*         In the definition of Updates graph, the authors mention that:
      A static network information resource (e.g., Cost Map,
      Network Map) may need only a single updates graph. A dynamic
      network information resource (e.g., Filtered Cost Map) may create
      an updates graph (within a new TIPS view) for each unique filter
      request.

How to understand cost map and network map as static network information resource? I don't see the 7285 making that distinction, I think the cost map information could be dynamically changing. Maybe you mean something else I failed to get, but I don't think there exists static network information resource on a time span.



*         The definition of snapshot/incremental update is a full/partial replacement of resource contained within an updates graph, but the word "replacement" sounds quite strange to me. Why it is a replacement? Could you clarify a little bit more? Or maybe you want to use generation/creation?



*         The definition for ID#i-#j:

      Denotes the update item (op, data) on a specific edge in the
      updates graph to transition from version at node i to version at
      node j, where i and j are the respective sequence numbers of the
      nodes the edge connects.
      What's the abbreviation for op, operation? I don't see this field in the ALTO message. The update item is defined as either a snapshot or incremental update, I don't know how this is related to (op,data).



*         The text below Information Resource Directory(IRD)

Figure 4 shows an example illustrating the TIPS abstraction.  Each

ALTO client (Client 1, Client 2, or Client 3) maintains a single HTTP

connection with the ALTO server.

s/Figure 4/Figure 1?  Also note that you described this figure as the TIPS abstraction, but the figure 1 title is "ALTO Transport Information".



*         Regarding Figure 1, I found that description of information resource #2 is lost, is this intentional? Maybe add some description for resource #2 to communicate the intent? Or simply remove it and rename resource#3 to resource#2.



*         Note that you also refer to network Map as static resource here, see my similar comments above.


*         Above Figure 1: tvi/ug = incremental updates graph associated with tsi
s/tsi/tvi?

Sec.3.1 Basic Data Model of Updates Graph

*         Mandatory incremental updates and optional incremental updates are mentioned in the explanation of Figure 2, but I never see this defined, so what is mandatory/optional incremental updates? What is the difference between mandatory and optional ones? Maybe point to some reference here, or clarify in the document.


Sec.3.2 Resource Location Schema

*         I guess I don't really understand what is a location schema. Maybe add a reference or more text for clarity.

*         At the very beginning of this section:

To access each individual update in an updates graph, consider the

   model represented as a "virtual" file system (adjacency list)...

In my opinion, it is not a real file system. The file system is a tree structure, each non-root node has and only has one parent, but in figure 3, for example, node 103 has both 0 and 102 as parents node, fine for a directed acyclic graph, but not a file  structure. Maybe I am wrong, but please check that.

*         It is not easy to understand your figure 3. At first I was struggling to understand what the indentation means for each number, and what the shortcut means. Then I've got some understanding which I am not sure is correct. Maybe you want to add more explanation for this figure.


Sec.3.3 Updates Graph Modification Invariants

*         Sorry, but I guess I still don't understand what the title means, what is the modification invariant?

*         You mentioned in the last paragraph that a server might compact a resource's update graph to save space, and [105,106] are valid set for server to save. But then what if a client requests content from 101 to 105? Doesn't this mean that resource state prior to 105 is no longer reachable for clients?


Sec.6.3 Open Example

*         The client sends a request to ALTO server, how its username and password is reflected on the request? It is the Authorization field? Maybe mention it more explicit like that: The user name and password are combined in the format of user:password and encoded using Base64 in the Authorization field. Otherwise I would rather not even mention this authorization thing.


Sec. 7.2.1.  Server Processing "Error" Conditions

*         For 429 error code: s/ "Re-Try After" headers/ "Retry After" headers/  (remove hyphen)



Sec7.4 New Next Edge Recommendation

*         s/recieve/receive/


Appendix B

*         last bullet: s/Section Section/Section/     (remove a "Section")


Best Regards,
Qiufang Ma