[Ibnemo] 答复: 答复: 答复: 答复: How to group/reuse definitions

[Xiayinben <[e-mail]>]

Hi Bert,

Thanks for initiating this topic, it is really interesting and important.
I think the key point of this topic is about the meaning of two word's and usage method:
"connection" and "connectivity"

In my understanding
"connection" stands for connected resource(physical or virtual), it is a real object. "connectivity" stands for reachability, it is a kind of status or policy. 
"connection" can implicitly expresses the existing of two points "connectivity". When user doesn't point out bandwidth of connection clearly, user uses connection as connectivity.

In your example,
	Node n1,n2,n3
	Connection n1,n2
	Connection n2,n3
Is there a "connectivity" between n1 and n3?
I think it depends on whether n2 can do transfer traffic for the other nodes, which is node's transfer property.
So the "connectivity" is decided by "connection" and middle node's transfer property.
But it also raises a problem that the "connectivity" is not intuitive.

Therefore, we also discussed should we separate "connection" and "connectivity" as two keyword in NEMO language.
But this letting the intent description becomes long-winded.
For example, a enterprise have tens branches, which need connect to headquarter and communication with each other.
If we express connectivity by connection and node's transfer property, user only need to describe tens connections between headquarter and branches.
If we separate connection and connectivity, user also need to describe hundreds full mesh connectivity between branches.

So far, we don't separate the connection and connectivity. 
Look forwarding to your opinions.

Best regards,
Yinben 

-----邮件原件-----
发件人: Ibnemo [mailto:[e-mail]] 代表 Bert Wijnen (IETF)
发送时间: 2015年11月18日 17:24
收件人: zhangyali (D); PEDRO ANDRES ARANDA GUTIERREZ; Zhoutianran; [e-mail]
主题: Re: [Ibnemo] 答复: 答复: 答复: How to group/reuse definitions

For me to better understand and form an opinion on the discussion, I would appreciate a few clear definitions for:

connection
   Is it that there is a physical or logical connection between 2 nodes?
   Is it only one of these, or can it be bother connectivity
   Is it direct connectivity or possibly via some other nodes/subnetwork
   Or a logical connectivity?

I have hear people say that "connection" means that connectivity is allowed.
Not necessarily that there is a phyisical or logical connection between 2 nodes/subnets So if we have
    node n1
    node n2
    node n3

and we have
    connect n1 to n2
    connect n2 to n3

then in my understanding n1 is physically/logically connected to n2 and n2 is physically/logically connected to n3

but in my view,n1 would be able to communicate with n3 But I have also heard that in order to do that, one would have to
    connect n1 to n3
And that would not necessarily mean that a physical/logical connection between n1 and n3 would be created, but just that it would allow n1 to communicate with n3 (routed via n2 of course).

I think it would be good to write down the exact definitions of what thinks like "Connection", "connect", "connectivity", etc mean

I think that can help teh discussion (at least for me, and possibly for some other who are not involved in implementations).

Thanks,
Bert




On 16/11/15 12:11, zhangyali (D) wrote:
>
> Thanks Pedro. I think our understanding for “connection” and 
> “connect/connectivity” is different. This topic has been discussed in our team many times. It’s really helpful for us to listen your views.
>
> First of all, I want to clarify the meaning of connection. It refers 
> to a kind of resources to allow the communication.  It’s not a 
> physical link, but a abstraction of objects depended on communication. For example, a tunnel can be seen as a connection. For each of connection, user could assign bandwidth on it or not.
>
> In your expression, “connect” refers to “connectivity” which specifies 
> the communication rules or logic connection rather than resources 
> depended on. (Please point it out if my understanding is wrong.)
>
> In fact, we have considered if we need a new keyword to express 
> connectivity, but there are some questions we need further consideration.
>
> 1.If connection does not have bandwidth parameter, do the connection and connectivity have the same meaning?
>
> 2.If the keyword of connectivity exists, when use the connectivity and when use connection?
>
> 3.If user have to express connection before expressing connectivity? 
> If not, do users know there are resources supporting for the connectivity?
>
> Looking forward to your opinions.
>
> Yali
>
> *发件人:*PEDRO ANDRES ARANDA GUTIERREZ 
> [mailto:[e-mail]]
> *发送时间:*2015年11月13日19:31
> *收件人:*zhangyali (D); Zhoutianran; Bert Wijnen (IETF); [e-mail]
> *主题:*Re: 答复: 答复: [Ibnemo] How to group/reuse definitions
>
> Comments inline
>
> *De: *"zhangyali (D)" <[e-mail] 
> <mailto:[e-mail]>>
> *Fecha: *viernes, 13 de noviembre de 2015, 10:59
> *Para: *paag <[e-mail] 
> <mailto:[e-mail]>>, Zhoutianran 
> <[e-mail] <mailto:[e-mail]>>, "Bert Wijnen 
> (IETF)" <[e-mail] <mailto:[e-mail]>>, 
> "[e-mail] <mailto:[e-mail]>" <[e-mail] 
> <mailto:[e-mail]>>
> *Asunto: *答复: 答复: [Ibnemo] How to group/reuse definitions
>
>     _[Yali] Our expressions of new DMZ are similar, except you omit parameter lists. And firewall and l2-group(L2Switch in your
>     expression, I think) are predefined node types, so I omit them._
>
>     _    A key point/difference is how to express the connection/connectivity between the two nodes. I think resource is a
>     essential element to allow the communication between nodes no matter where it is, that is, if there is not "real" connection
>     between nodes, they will not be connected._
>
> Sorry, but I would distinguish a ‘logical patch panel’implemented in 
> an Open VirtualSwitch inside a server blade or even inside a data 
> centre supporting SDN, NFV, etc. from a real link (i..e. my second example). Why? Because these connections have no specific characteristics, while a "connection over a cable”has characteristics like Bandwidth etc.
>
>     _    And what if user wants to assign a bandwidth in this connection? So I am not sure if the "Connect" includes enough
>     information._
>
> The Connect is used when I have no specific requirements. In an 
> example related more to ETSI/NFV, I could see the Connect as the logical connection between Virtual Network Function Components (VNFCs) inside a VNF.
>
> My .02 cents, /PA
>
> ---
>
> Dr. Pedro A. Aranda Gutiérrez
>
> Technology Exploration -
>
> Network Innovation & Virtualisation
>
> email: pedroa d0t aranda At telefonica d0t com
>
> Telefónica, Investigación y Desarrollo
>
> C/ Zurbarán,12
>
> 28010 Madrid, Spain
>
> Fragen sind nicht da, um beantwortet zu werden.
>
> Fragen sind da, um gestellt zu werden.
>
> Georg Kreisler
>
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