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Re: [paws] Gen-art LC review: draft-ietf-paws-protocol-12

2014-07-08 21:22:28
Robert,

Thanks again for the review. I have place comments, questions, suggested
text inline for each of your comments.
Please take a look.

-vince


On Thu, Jul 3, 2014 at 10:28 AM, Robert Sparks 
<rjsparks(_at_)nostrum(_dot_)com> wrote:

I am the assigned Gen-ART reviewer for this draft. For background on
Gen-ART, please see the FAQ at

<http://wiki.tools.ietf.org/area/gen/trac/wiki/GenArtfaq>.

Please resolve these comments along with any other Last Call comments
you may receive.

Document: draft-ietf-paws-protocol-12
Reviewer: Robert Sparks
Review Date: 3 July, 2014
IETF LC End Date: 7 July, 2014
IESG Telechat date: 10 July, 2014

Summary: This document is not ready for publication as a Proposed Standard.

I apologize in advance if I've missed where one of the questions below is
already answered. There's a lot to take in here.

Major Issues

- The document says it "describes" the use of HTTP/TLS as the transport
for the protocol. Was it the intent to allow others? If not, the language
should be firmed up.


The protocol messages are meaningful independent of the transport, so we
did not want to prohibit others. It that frowned on?



- The document still says "TBD Define message format" in the section on
Listing Servers. I understand from reading the list that what the document
is going to say about Listing Servers is going to change (to not include
how you talk to them?). This change needs to be finished before the
document can be reviewed for completeness.


Noted. Will ask again on the list.



- It's not clear when a server should use the HTTP level redirection
discussed in section 7 vs the databaseChange mechanism in the protocol's
responses. There should be some discussion about what the Device should do
when the databaseChange mechanism results in a redirect loop.


Thanks for pointing this out. I propose removing the HTTP-level 301 Moved
Permanently mechanism and only have the databaseChange mechanism.

Proposed modified text in Section 4.1:
   A Database MAY indicate that its URI will be changing by including
   the URI of one or more alternate databases (See DbUpdateSpec
   (Section 5.7)) in its responses to a Device.  Before a Database
   ceases operation, for example, it MUST include DbUpdateSpec in its
   responses to notify Devices.  A Device will update its preconfigured
   list of databases to replace (only) its entry for the responding
   Database with the URIs of the alternate databases; the list of
   alternate databases does not affect any other entries.  Note that the
   ordering of databases in the list does not imply any preference and
   does not need to remain the same for every request.  The Device
   SHOULD detect infinite redirection loops; if a suitable database
   cannot be contacted, the Device MUST treat this as equivalent to a
   response indicating no available spectrum.




- The document needs to be clear where the primitive types (like string,
float, and integer) in the UML-ish diagrams in section 4 are defined. I'm
guessing from context that you're assuming the definitions in RFC4627. If
that's true, there are several places that you talk about string where your
text should change. RFC4627 says string is UNICODE, and may be encoded many
ways (see section 3 of that document). If your intent is to restrict all
strings to UTF-8 encoding say that, and adjust the text you currently have
that mentions UTF-8. (The various places where you say a string MAY contain
UTF-8 do not make sense - if you're assuming the encoding is UTF-8 and
trying to reinforce that there may be non-ASCII range UTF-8 here, say that
explicitly). There are other related phrases that don't make sense such as
where you say things like "The length of the string MUST NOT exceed 64
US-ASCII characters."


OK. Specified UTF-8 and removed meaningless statements.

Proposed added text in Section 4:

   The parameter tables in this section and Protocol Parameters
   (Section 5) are for reference and contain the name of each parameter,
   the data type of each parameter, and whether the existence of the
   parameter is required for the protocol transaction in question.  The
   diagrams are loosely based on UML, and the data types are defined
   either in Protocol Parameters (Section 5) or are one of the following
   primitive or structured types:

   string  A string, as defined by The JavaScript Object Notation (JSON)
      Data Interchange Format [RFC7159], restricted to the UTF-8
      encoding.

   int  A number, as defined by The JavaScript Object Notation (JSON)
      Data Interchange Format [RFC7159], without a fractional or
      exponent part.

   float  A number, as defined by The JavaScript Object Notation (JSON)
      Data Interchange Format [RFC7159].

   boolean  A boolean, as defined by The JavaScript Object Notation
      (JSON) Data Interchange Format [RFC7159].

   list  A structured type the represents a list of elements, as defined
      by The JavaScript Object Notation (JSON) Data Interchange Format
      [RFC7159] array type.  For each list parameter, its diagram and
      description include a reference to the data type its list
      elements.  The diagram notation and description may include
      additional constraints, such as minimum or maximum number of
      elements.

   NOTE: All parameter names are case sensitive.  Unless stated
   otherwise, all string values are case sensitive.


- The descriptions of messages in section 4 all contain *other:any. None
of those are reflected in the concrete schema of section 6. Should they be?


This was intended to be capture by the note in Section 6:

   NOTE: In general, all messages defined in this section are extensible
   by adding additional properties to support ruleset-specific and
   database-specific requirements.  In all cases, the Device or Database
   MUST ignore any parameter it does not understand.



- The INIT_RESP description requires one or more RulesetInfo objects. What
is a database supposed to do if it has no rulesets to return (possibly
because it doesn't have anything overlapping with the list of ruleset IDs
listed in the DeviceDescriptor in the INIT_REQ.). Should this have been
0..* (along with the corresponding change to the text), or is there an
Error that the database should return when this happens. If the latter, it
would be good to call it out in 4.2.2.


This was indicated in the prior section for INIT_REQ, but propose adding
the following as first paragraph:

   The initialization response message communicates database parameters
   to the requesting device.  This response is returned only when there
   is at least one ruleset.  Otherwise, the Database returns an error
   response, as described in INIT_REQ (Section 4.2.1).




- Section 4.4 talks about returning OUTSIDE_COVERAGE when the location
specified in the request is outside the regulatory domain (could that be
domains?) supported by the database. The sections on init and registration
(4.2 and 4.3) don't have this discussion. Should they?


Yes. Added to those requests. Thanks.



- A databaseChange (at least as described in 4.4) can provide one or more
alternate database URIs, affecting the Device's configuration. When there's
more than one, is there any preference to what order the Device should try
to use them in? Is there any expectation that they will give the same
answers to a given request? If not, do you want to say anything about
discouraging devices from asking all the databases it knows about to find
an answer it likes best?


In general, there should be no difference in answers, because each Database
must also conform to the regulatory rules. There is no significance implied
by the list ordering. On the other hand, I don't think we need language
discouraging devices from asking multiple databases, since they should have
an understanding of the rules as well.

See proposed text above that contains:

   Note that the
   ordering of databases in the list does not imply any preference and
   does not need to remain the same for every request.



- If the requirements to act as if there is no available whitespace when
you can't reach a Listing Server remain in the document, the security
considerations should call out that any attack that would prevent reaching
a Listing Server would result in all devices relying on that Listing Server
ceasing their use of any whitespace.


Thanks. Added.



- Please check the description of 'timeRange' in section 5.9
(SpectrumSpec). I think you meant to say "in which there is _NO_ available
spectrum".


Thanks for the catch!



- The definition of SpectrumProfile (section 5.12) needs clarification. Is
this allowed?
  "profiles" : [
    {"hz": 5.18e8, "dbm": 30.0 },
    {"hz": 5.24e8, "dbm": 37.0 }
  ]
If so, what does it mean? Do I do linear interpolation between points
(33.5 dbm (~2.25 watts) at 521Mhz)?
Similarly, does this specify a ramp up and then back down? (shaped like a
^)?
  [
    {"hz": 5.18e8, "dbm": 30.0 },
    {"hz": 5.21e8, "dbm": 33.5 },
    {"hz": 5.24e8, "dbm": 30.0 }
  ]
If not, what text disallows it?


This is explicitly allowed. We changed the encoding to allow this. Propose
modifying the first paragraph of  5.12 to the following:

   A spectrum profile is characterized by an ordered list of (frequency,
   power) points that represents the shape of maximum permissible power
   levels over a range of frequencies as a piecewise linear curve.

Also add after the list of constraints:

   NOTE: This encoding allows presentation of "ramps" where the slope of
   a line segment may be finite and non-zero.



- You are using the schema language defined in draft-zyp-json-schema to
define your message format. That makes it a normative reference. The draft
is expired - are there plans to progress it?


Yikes. The intent is not to define a strict, formal schema, but just to
have a way of defining the messages in a concise fashion.
Do you have a recommendation of what to do here? Are the descriptions
self-explanatory enough? or do I have to define
the "schema language".



- Something needs to talk about case-sensitivity of the various protocol
elements. JSON-RPC says that member names are case sensitive and is
otherwise silent. The string "sensitive" doesn't appear in RFC4627. So, you
have an example that says "authority":"us". Is that the same as
"authority":"US", and where does the spec answer that question? My read of
JSON-RPC says that "authority":"us" and "Authority":"us" are _not_ the same
thing, and that the second would not be a recognized property of a
RulesetInfo object.


You're right. See above proposed text defining the primitive types.



Minor Issues

- I'm not finding where you define the protocol version. I see "1.0" in
the json examples in section 6. Where is it specified? Within a given
method, the only extension point I find other than changing the protocol
version is the *other concept in messages, which MUST be ignored when
either side doesn't understand them. So there should be some discussion
about what kind of change would require the protocol version number to
change. Suppose you wanted to allow batching requests from several slaves
into one request to the database (similar to AVAIL_SPECTRUM_BATCH_REQ but
allowing a list of DeviceDescriptors perhaps). Does this require a new
protocol version, or is it just a new request type in this version? If you
think it's a new request-type, should there be a request and response type
and/or method registry?  And yes, I see how you could do this with JSON-RPC
batch, but if that's where you'd send this idea, why didn't you do
AVAIL_SPECTRUM_BATCH_REQ that way? (Possibly related: I can't figure out
what "The initialization message also represents extension points for
database implementations or rulesets that require the explicit handshake."
is trying to say. Can you rephrase that more simply?)


Good point. Propose adding a new section:

4.2.  PAWS Version

   PAWS version uses a "<major>.<minor>" numbering scheme to indicate
   versions of the protocol.  The protocol versioning policy is intended
   to allow the Device or Database to indicate the format of a message
   and its understanding of PAWS functionality defined by that version.
   No change is made to the version string for the addition of message
   components which only add to extensible field values.  The <minor>
   number is incremented when the changes made to the protocol add
   functionalities (methods), but do not change the existing
   functionalities.  The <major> number is incremented when incompatible
   changes are made to existing functionality.

   The current PAWS version is "1.0".



- It's not clear what it means to "support" a ruleset. I infer that this
means that the device has code that implements what's required by the name.
Can you state that explicitly? Does a Master device have to have this code?
Could it simply be a box that only serves to answer requests from Slave
devices? If so, why does it care what the rulesets actually are. If a slave
can ask and a database can answer, should a master just shovel the bits, or
is there a requirement that the master device be configured to handle a
ruleset before a slave can ask about it?


OK. Propose update Terminology section to distinguish between "ruleset" and
"ruleset identifier":

   Ruleset:  A ruleset represents a set of rules that governs the
      operation of white space devices and Spectrum Databases.  A
      regulatory authority can define its own set of rules or adopt an
      existing ruleset.  When a Database or Device is said to "support a
      ruleset", it means that it contains out-of-band knowledge of the
      rules and that its hardware and software implementations conform
      to those rules.

   Ruleset Identifier:  A ruleset can be identified by an IANA-
      registered identifier (see PAWS Ruleset ID Registry
      (Section 9.1)).  When a Database or Device indicates it supports a
      ruleset identifier, it means that it conforms to the rules
      associated with that identifier.  A regulatory authority can
      define and register its own ruleset identifiers, or it can use a
      previously registered identifier if it adopts an existing ruleset.



- In the last paragraph of section 4.1 (before 4.1.1 starts), "If the
Device is already operating" assumes that the device could only be
operating if it had previously contacted some database. The problem is that
the device was able to reach a database at one point and now it can't reach
any.  It would read more clearly if you said that explicitly.


Proposed change:

   If the Device had previously contacted a database to get available
   spectrum, but subsequently fails to contact a suitable database, the
   spectrum the Device is currently using can be used for as long as the
   spectrum data is valid; ...



- Please point somewhere for a definition of the terms 'uncertainty' and
'confidence' (I suggest draft-ietf-geopriv-uncertainty). The GEOPRIV
working group has gone through many iterations of disagreement about what
these terms mean and how they should be used. For a taste, skim some of <
https://mailarchive.ietf.org/arch/search/?email_list=geopriv&q=uncertainty>.
If you don't point to a hard definition, your implementation community will
have to go through the same arguments.


Done. Although regulatory authorities may prescribe their own definitions.



- Should the security considerations section talk about the risk of
collisions in serialNumber (since it is the only required element in
DeviceDescriptor, and isn't a particularly secret thing)? Is there any harm
at the database if two devices innocently end up sending the same serial
number (without providing any of the optional information that would
otherwise disambiguate the devices)? Can a device learn anything useful
about another device by spoofing it? Is it possible that in some regulatory
realm, some devices would get more access than others, encouraging devices
to ask about what their competition gets to do? Can harm be done by a
device sending SPECTRUM_USE_NOTIFY messages claiming to be some other
serial number (and perhaps manufacturer) maliciously? I think this needs
more discussion than what RFC6953 contains.


Re: Available spectrum.
  The available spectrum depends on device type and location, not on serial
number. Consequently, there is no advantage to spoofing, and there would be
no additional information to be gained on spoofed devices.

  If, in the future, there is some regulatory realm that would set up rules
differently, then I think security considerations would be extended to
handle those cases.

Re: SPECTRUM_USE_NOTIFY
  I suppose this depends on the specific regulatory domains (or database
implementations) that require it. Currently there is no harm, since
notifications do not change the available spectrum answers that the
Database returns to devices.

So should I add these statements to the Security Considerations section?



- The use of the "id" parameter from JSON-RPC deserves more discussion.
The JSON-RPC spec allows it to be string, numeric (without a fractional
part), NULL or missing. You've chosen to require it (since you're not using
json-rpc notifications), and not allowing numeric values (why?). Are you
making any other assumptions about what it should contain? I think you're
assuming a level of uniqueness that would let you use the Batch mechanism
in section 6 of JSON-RPC (otherwise, the HTTP request/response context is
enough to associate the request and response and the id might as well be
constant).


Purely as a practical matter, handling a known type is easier than
multi-type. It should improve interoperability. Otherwise, its value
remains opaque to the Database.

What is your recommendation here?



- Section 7 says a server can reject a GET with a 404 - wouldn't that have
consequences for a later POST? Why wouldn't it use a 405?


Yes, it's supposed to be 405.



- The draft calls for the creation of a special list for review requests
for the IANA assignments. This may be ok (mailing lists are easy to set
up), but is there not an existing list that would serve the purpose just as
well?


I do not believe there is an existing list, unless it's standard practice
to re-use this discussion group (paws(_at_)ietf(_dot_)org).



Nits

- RFC 2616 has been obsoleted - the references should be updated.


Updating to RFC 7231



- It would help to have an example of a ruleset in the definition in the
Terminology section and perhaps for that definition to more strongly convey
that it is a name in a namespace, and what that rule means is elsewhere.
 (Right now the definition says that the ruleset is the actual set of
rules, not a name, and it made reading the protocol overview much harder
than it needed to be). At the very least, pointing to the examples in
section 9 early would help.


See proposed text of Terminology above.



- Is the document loosely borrowing UML, or are the diagrams used in
section 4 of a format formally defined in some other RFC? A pointer to a
definition of the format, or a brief description noting it's based on UML
along with where the base types are defined would be useful.


See proposed text of primitive types above. Do I need a reference to UML?



- "One approach to manage spectrum sharing" is awkward. Would "One
approach to managing spectrum sharing" or "One approach to the management
of spectrum sharing" work?


Thanks. Changing to "One approach to managing spectrum sharing"



- There are several instances of "The Device needs to use the information
to update its list". Consider clarifying 'needs to'. Should this have been
MUST?


These were changed based on comments from our AD (Pete), since they are not
a protocol requirement.


- "The vertices MUST be defined in a counter-clockwise direction" assumes
you are looking at them from above - please be explicit.


Thanks. Adding clarification.



- Section 9.1.2's first paragraph should say "FCC and ETSI" the same way
9.2.2 does. You could generalize that to "any particular set of
authorities".


Thanks for the suggestion. Changing both to "any particular set of
authorities".



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-- 
-vince