Subject: [Supa] review of draft-cheng-supa-ddc-use-cases-01

From: Juergen Schoenwaelder <[email-masked]>
Date: Mon, 8 Dec 2014 15:21:49 +0100

Hi,

I have read draft-cheng-supa-ddc-use-cases-01 and here are some
comments.

a) You introduce the term "Distributed Data Center" and "Internet Data
   Center". I am not sure how these terms relate to each other. There
   is a pointer to draft-karagiannis-supa-problem-statement-02 but
   then this document uses the term "Inter-Data Center". So do all
   these terms mean the same or are there subtle differences?   

b) It is not clear what 'DDC traffic' is. Is this the traffic between
   DCs, excluding any user traffic to/from DCs? What does it mean to
   'schedule' DDC traffic - I assume this is only possible within
   bounds for certain kinds of DDC traffic.

c) When you talk about Value Added Services (VAS) and the creation and
   deletion of VAS, do you include the life-cycle management of service
   instances (e.g. virtual machines) or are you strictly focusing on
   the network aspects?

d) What does ABPD stand for?

e) There is a reference to I-D.adel-supa-configuration-model which I
   can't resolve. Did you mean draft-zaalouk-supa-configuration-model?

f) I do not understand the bandwidth waste argument in section 5 if
   shortest paths are used. The example that you provide is that link
   T1 is only to be used up to a utilization of 80% and then a
   secondary path comes into play. This is a policy I assume. It is
   not clear from the text who imposes this policy. If it is the
   network provider, does setting up VPNs really change the routing
   policy? If the network operator wants to run the links at 80%
   capacity max, will he not find ways to enforce that? Is the idea
   that policies work against each other in this case? Or am I
   mis-understanding the example?

g) For the use case in section 6, why do I need to run the
   synchronization over a special VPN tunnel? What happens if the
   synchronization does not finish within the lifetime of the VPN
   tunnel?

h) The use case in section 7 talks about Skype but then I wonder which
   role Skype plays _between_ data centers. Anyway, there has been
   lots of QoS work in the past. If your goal is to have low latency
   services between DCs, why would the proposed system do better than
   what got invented in the past?

i) The last use case described in section 8 seems to be talking about
   bundling path capacity. How does this related to the use case
   describe in section 5? Are there again multiple actors involved? If
   so, do you envision that the network and DC operators
   collaboratively work together to optimize their policies or do you
   assume that DC operator policy tries to trick^Hoptimize the network
   operator policies?

I guess the biggest question I have is about who are the independent
parties involved, how much policy do the independent parties control
themselves, which policy interfaces to the parties expose to others,
and what happens if policies do not necessarily align with each
other. In case you plan to revise this I-D, it may make sense to be
more explicit about the parties involved and what they control and
expose to other parties.

/js

-- 
Juergen Schoenwaelder           Jacobs University Bremen gGmbH
Phone: +49 421 200 3587         Campus Ring 1, 28759 Bremen, Germany
Fax:   +49 421 200 3103         <http://www.jacobs-university.de/>