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

[Qin Wu <[e-mail]>]

Hiya
-----邮件原件-----
发件人: Scharf, Michael (Nokia - DE) [mailto:[e-mail]] 
发送时间: 2016年7月11日 18:16
收件人: Qin Wu; [e-mail]
主题: RE: New Version Notification for draft-wu-opsawg-service-model-explained-00.txt

Hi Qin,

Thanks for your reply. Inline some further comments [ms2].

> 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.

[ms2] I am not sure if I can follow. My point is that the wording "describes a service and all of the parameters" seems contradicting given the use of the term "all" if you exclude SLAs. Also, Section 5 does not really have a well-defined definition - excluding some examples does not necessarily result in a precise definition. (I agree that "Service" is challenging to define but maybe this could be one reason to find an alternative term to "service model"). 

[Qin]: As we clarified Service Level Agreements (SLAs) have a high degree of overlap 
 with the definition of services present in service models, but we don't want to cover a number of fine-grained details of attributes defined in SLA for the reason given in section 5.
 That's why we add a constraint after " describes a service and all of the parameters " to limit these parameters to abstract level and operator independent way. Maybe we could add
some text to make this more clear.

> 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.

[ms2] My point is that SLA parameters may be an important part of the customer-service provider agreement of a service and it is surprising to first seeing this mentioned at the end of Section 5.
 
[Qin]: Sure, to avoid confusion with the service defined in the model, as I mentioned above, we use the different term for these Quality related parameters.

> [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.

[ms2] Sure, but what is the role of a service model defined in YANG e.g. when the human relies on CLI or scripts? To me this wording does not explain this well.

[Qin]: why we should tie service model definition with YANG, the service model is just a service template, you can use human readable language to express it or you
Can use machine readable language to express it, it doesn't matter. Therefore, in some cases, you just need fill the service parameters in some kind of form and submit this form
to the server for further parsing and interpretation.
 
> *** 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.

[ms2] You may want to add that assumption more explicitly to the text and possibly add that this is only one potential architecture. 

[Qin]: We give two optional architecture in the figure 2 and figure 3, let us know if there is any potential architecture we are missing.
> *** 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.

[ms2] Well, I think you should comment on SLAs in Section 2 to avoid confusion.

[Qin]: Done, see above.

Michael



> *** 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:[e-mail]] On Behalf Of Qin Wu
> Sent: Tuesday, July 05, 2016 2:02 PM
> To: [e-mail]
> 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: [e-mail] [mailto:[e-mail]]
> 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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