The cost-calendar draft is ready. It is an excellent piece of work by the
authors who are long standing ALTO contributors; the draft is is applicable
and of interest to many ALTO deployments (and this should be highlighted; I
provide the Unicorn link to highlight this in my feedback below, but
please provide more). The one feedback I have about the draft is the need
for a thorough edit session to ensure grammar and consistency in the
document as well as to ensure that implementations deal with as less
ambiguity as possible when following the protocol extension. I provide
some examples of where the text can be improved below.
- General:
a) Is it Cost Calendars (plural) or Cost Calendar (singular)? You use
both in
the text; best to ensure that only one representation is being used.
b) There are a number of run-on sentences (see first, second and third
paragraphs in S3.1; such run-on sentences make it very hard to understand
what
is being asked of the implementors, and as a result will lead to an
implementation that is ambiguous at best and full of bugs in the worst
case.
Such sentences must be scrubbed appropriately before publishing as these
outline normative behaviour).
Getting the right text to describe the processing of cost-calendar is not
easy,
I will be the first to admit. Perhaps an editor can improve the text to
eliminate such run-on sentences.
c) In many HTTP requests and responses (see for example the ALTO POST
request
on page 19), a content length is specified. In the example on page 19,
the C-L
is 815. However, how was this sum arrived at? The body of the response
contains a lot of elucidations ("v1, v2, ..., v12"), for example. Does
the 815
bytes include these elucidations ("...")? My advice would be to be as
realistic as possible and remove these elucidations, put sample values in
the
response and calculate the C-L. Yes, more work, but better product.
Document-order specific comments follow.
- Abstract:
a) s/service such that/service so that/
b) s/ALTO Cost Calendars/ALTO Cost Calendar/
- S1, para 1: s/needing to/that need to/
- S1, para 2: The larger point you are making in the second half of the
paragraph is that due to the fact that ALTO does not provide real time
network
metrics, the applications essentially have to figure out what the cost of
doing business will be at some later time, a proposition that is
sub-optimal
since the application has no idea of network usage at some future time.
This
salient point is not quite captured. Perhaps the text below may help?
(Please feel free to edit as needed.) Also, you have the wrong reference
to
ALTO requirements document in your current text; that is fixed below as
well.
OLD:
ALTO intentionally avoids provisioning real-time information as explained
in
the ALTO Problem Statement [RFC5693] and ALTO Requirements [RFC5693].
Thus
the current Cost Map and Endpoint Cost Service are providing, for a given
Cost
Type, exactly one path cost value. Applications have to query one of
these
two services to retrieve the currently valid cost values. They,
therefore,
need to plan their ALTO information requests according to their own
estimation
of the frequency of cost value change.
With [RFC7285], an ALTO client should interpret the returned costs as
those at
the query moment. However, Network costs can fluctuate, e.g., due to
diurnal
patterns of traffic demand or planned events such as network maintenance,
holidays or highly publicized events. Providing network costs for only
the
current time thus may not be sufficient, in particular for applications
that
can schedule their traffic in a span of time, for example by deferring
backups or other background traffic to off-peak hours.
NEW:
For the reasons outlined in the ALTO problem statement [RFC5693] and
requirement AR-14 [RFC6708], ALTO does not disseminate network metrics
that
change frequently. In a network, the costs can fluctuate for many reasons
having to do with instantaneous traffic load or due to diurnal patterns of
traffic demand or planned events such as network maintenance, holidays or
highly publicized events. Thus, an ALTO application wishing to use the
Cost
Map and Endpoint Cost Service at some future time will have to estimate
the
state of the network at that time, a process that is, at best, fragile and
brittle since the application does not have any visibility into the state
of
the network. The need of such future scheduling of large scale traffic
that
can be addressed by the ALTO protocol is motivated by Unicorn, a unified
resource orchestration framework for multi-domain, geo-distributed data
analytics [draft-xiang-alto-multidomain-analytics].
- S2, para 2: s/crowded events/expected spike in traffic due to crowd
gathering
(concerts, sports, etc.)/
- S2.1, para 1:
a) s/with dateless/without date/
b) s/the "meta" of/the "meta" section of/
c) s/avoiding to process useless requests./reducing processing of similar
requests./
- S2.2, para 2: s/also says/states/
- S2.2,
a) s/and ensure/and to ensure/
b) para 4: "As recommended, it relies ..." ==> Recommended by who? Please
specify.
- S2.2.2:
OLD:
As a consequence, when a metric is available as a Calendar array, it
MUST be as well available as a single value, as provided by
[RFC7285].
NEW:
As a consequence, when a metric is available as a Calendar array, it also
MUST
be available as a single value as required by [RFC7285]. (This ensures
backwards compatibility.)
- S3.1, para 1, 2, and 3: I would re-write these paragraphs completely,
probably
put them in one pragraph. In its current form, it is hard to parse and
understand these paragraphs.
My suggested edit is below, but please feel free to modify as needed.
A Cost Calendar for a given Cost Type MUST be indicated in the IRD by an
object of type CalendarAttributes. A CalendarAttribute object is
represented
by "calendar-attributes" member of a resource entry. Each
CalendarAttributes
object applies to a set of one or more cost types. A Cost Type name MUST
appear no more than once in the "calendar-attributes" member of a resource
entry; multiple appearances of a Cost Type name in CalendarAttributes
object
of the "calendar-attributes" member causes the ALTO client to ignore any
occurrences of this name beyond the first encountered occurrence.
- S3.2, para 1: "w.r.t." ==> Too colloquial to be in a standard document.
Please take out or reword the sentence.
- S3.3:
a) first bullet: s/at the IANA./with IANA.
b) in the remaining bullets, s/some fictitious/a fictitious/
- S3.3, after the GET request, what is the horizontal line doing? It
appears to
be separating the request and the response, if so, please use the "S ->
C" and
"C -> S" nomenclature used in other IETF documents to denote request going
from Client to Server and response from Server to Client.
- S4, para 2 does not make sense grammatically. Please reword.
- S4.1.3, para 1: s/periods for example to/periods to/
- S4.1.3, para 3: s/To lighten the text/For representation brevity/
Thanks.
- vijay
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