Re: [OPSAWG] New Version Notification for draft-wu-opsawg-service-model-explained-00.txt

-----邮件原件-----
发件人: Scharf, Michael (Nokia - DE) [mailto:michael.scharf@nokia.com] 
发送时间: 2016年7月7日 21:47
收件人: Qin Wu; opsawg@ietf.org
主题: RE: New Version Notification for draft-wu-opsawg-service-model-explained-00.txt

Hi all,

I have quickly scanned this document. Some initial comments [ms]:

*** Page 3:

   Service Model:  A service model is a specific type of data model.  It
      describes a service and all of the parameters of the service in a
      portable, operator-independent way.  It can be used by a human or
      by software to configure or request a service and may equally be
      consumed by a human or by a software component.

[ms] I would suggest a more careful wording regarding the completeness of the model, e.g., "It aims at describing a service and all of the parameters of the service...". As discussed in L3SM in the past, for certain services (e.g., firewalls, DoS prevention, ...) the service model would have to be extended / augmented. Also note that the statement "all parameters" contradicts the statement on SLAs later in the text.

[Qin] What the service is has been well defined and clarified before service model definition in the section 2.
That is to say, Firewall and DoS prevention are just additional functionalities that are used to enhance the basic service we defined in the document.
For what the service is not is further clarified in the section 5, the first bullet.

In addition, we don't take SLA fine granularity details combining commercial terms as service parameters, so I don't see there is inconsistency issue, for some misconception on the service model
Understanding is clarified in the different section, this is intentional.

[ms] I find the wording "it can be used by a human..." confusing. Is the assumption that a user would manually type in a service request resulting in a valid data model, e.g., by manually typing in NETCONF commands? I would rather write something like "the parameters can be entered by software or also manually by a human..."

[Qin]: what we try to convey here is Human can rely on CLI,script or other human readable language to define a service, request the service, but such parameter will not directly implemented by network element.

*** Page 3:

   The encoding and communication protocol used to exchange a service
   model between customer and network operator are deployment- and
   implementation-specific.  The IETF recommends the use of the NETCONF
   Configuration Protocol [RFC4741] with data encoded in XML or JSON for
   interactions "on the wire" between software components.  However, co-
   located software components might use an API, while systems with more
   direct huan interactions might use web pages or even paper forms.

[ms] I am not sure if the IETF should suggest the use of NETCONF on the northbound interface of a "service orchestrator", which seems to be the scope of this document. Are there pointers to running code that actually do that? I would rather prefer a wording such as "The IETF has standardized NETCONF and RESTCONF for interactions "on the wire" between software components".

[Qin]: You are right, I think RESCONF is recommended on the northbound interface of a service orchestrator, your proposed change looks good. Thanks.

*** Page 7:

   o  The network operator may use further data models that help to
      describe how the service is realized in the network.  These models
      might be used on the interface between the Service Orchestrator
      and the Network Orchestrator as shown in Figure 3 and might
      include many of the pieces of information in the service model
      alongside protocol parameters and device configuratin information.
      It is important that the Service Orchestrator should be able to
      map from a service model to these data models, but they are not
      the same things.

[ms] Why is it not possible that the data models are the same? In Figure 3, the "service orchestrator" is actually a "client" (read this as "customer") of the "network orchestrators". Inside an operator, the "service orchestrator" could be operated by a different organization than the "network orchestrator", i.e., there ould even be a business relationship. In general, architectures can be recursive. I think this statement requires further explanation or rewording.

[Qin]: The concept to split Orchestrator into service orchestrator and network orchestrator, is the service orchestrator is network agnostic while network orchestrator is network aware.
Service model consumed by the service orchestrator could be different from the data model consumed by network orchestrator since network orchestrator need to decide what network device is selected, which protocol is enabled, which technology is used, which network interface or port is assigned. The service orchestrator doesn't need to care about the underlying technology or what protocol is available.

*** Page 7:

   o  Service Level Agreements (SLAs) have a high degree of overlap with
      the definition of sevices present in service models.  Requests for
      specific bandwidth, for example, might be present in a service
      model, and agreement to deliver a service is a commitment to the
      description of the service in the service model, however, SLAs
      typically include a number of fine-grained details about how
      services are allowed to vary, by how much, and how often.  SLAs
      are also linked to commercial terms with penalties and so forth,
      and so are also not good topics for standardization.

[ms] I wonder if it could make sense to distinguish between SLA and Service Level Objective (SLO) or Service Level Requirement (SLR). While I agree that it is difficult to standardize commercial terms, this IMHO partly contradicts the positioning of the term "service model" earlier in the document. Maybe the scope of the definition of "service model" has to be narrowed down?

[Qin]: We have clarified what the service is in the section 2 and Our service model definition aligns with service definition. Yes, we need to distinguish SLA from Service Level Objective/Requirement, but not necessary introduce another new term. We have clarified their difference in the text you quoted.

*** page 9:

6.4.  Supporting Multiple Services

   Network operators will, in general, offer many different services to
   their customers.  Each would normally be the subject of a separate
   service model.

[ms] The actual question here is if there could be communality between service models for similar services. That problem cannot be solved by this document but the text could e.g. explain that for a customer it can be confusing if separate service models model related concepts in different ways. 

[Qin]: That is a good question, I hope some building blocks specified by one service model can be reused in another service model.
Unfortunately we don't have too many YANG models that are used to model service in the IETF. We could cover this in the next version if more such service models are needed.

Thanks

Michael

-----Original Message-----
From: OPSAWG [mailto:opsawg-bounces@ietf.org] On Behalf Of Qin Wu
Sent: Tuesday, July 05, 2016 2:02 PM
To: opsawg@ietf.org
Subject: Re: [OPSAWG] New Version Notification for draft-wu-opsawg-service-model-explained-00.txt

Hi,
We have submitted a new I-D that discusses the scope and purpose of service models within the IETF and describes how a service model can be used by a network operator.
https://datatracker.ietf.org/doc/draft-wu-opsawg-service-model-explained/

In addition, this draft clarifies the role and position of service model in the SDN architecture and Clear several misconception on the service model.

Your questions and comments are welcome.

Regards!
-Qin
-----邮件原件-----
发件人: internet-drafts@ietf.org [mailto:internet-drafts@ietf.org]
发送时间: 2016年7月5日 19:55
收件人: Liushucheng (Will); Adrian Farrel; Liushucheng (Will); Qin Wu
主题: New Version Notification for draft-wu-opsawg-service-model-explained-00.txt

A new version of I-D, draft-wu-opsawg-service-model-explained-00.txt
has been successfully submitted by Qin Wu and posted to the IETF repository.

Name:		draft-wu-opsawg-service-model-explained
Revision:	00
Title:		Service Models Explained
Document date:	2016-07-05
Group:		Individual Submission
Pages:		12
URL:            https://www.ietf.org/internet-drafts/draft-wu-opsawg-service-model-explained-00.txt
Status:         https://datatracker.ietf.org/doc/draft-wu-opsawg-service-model-explained/
Htmlized:       https://tools.ietf.org/html/draft-wu-opsawg-service-model-explained-00

Abstract:
   The IETF has produced a considerable number of data models in the
   YANG modelling language.  The majority of these are used to model
   devices and they allow access for configuration and to read
   operational status.

   A small number of YANG models are used to model services (for
   example, the Layer Three Virtual Private Network Service Model
   produced by the L3SM working group).

   This document briefly sets out the scope of and purpose of an IETF
   service model, and it shows where a service model might fit into a
   Software Defined Networking architecture or deployment.

Please note that it may take a couple of minutes from the time of submission until the htmlized version and diff are available at tools.ietf.org.

The IETF Secretariat

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