Re: [Netslices] Reliability & Availability in NetSling

Well, we do need a definition to point to even if we reuse an existing 
definition. That way we all have a common understanding of the term and 
can provide a common explanation to the tenants.

- Stewart

On 14/08/2017 04:53, qiangli (D) wrote:
>
> Hi Stewart and All,
>
> Thank you for your suggestion. According to your information, it seems 
> that the words “reliability” is more suitable for the context of 
> network slicing with SLA guarantee.
>
> As Liang mentioned, industrial verticals and other partners have 
> different views on “reliability”. Even within IETF, different WGs may 
> have different understandings. A standardized definition of 
> “reliability” in NetSlicing scope is quite necessary IMHO, then NS 
> service provider can further classify the “reliability” and adopt the 
> appropriateimplementation technology accordingly. I would like to know 
> your opinion on this, and do we need to define the slicing specific 
> “reliability”?
>
> Best regards,
>
> Cristina QIANG
>
> *From:*Stewart Bryant [mailto:stewart.bryant@gmail.com]
> *Sent:* Friday, August 11, 2017 4:26 PM
> *To:* qiangli (D); netslices@ietf.org
> *Subject:* Re: [Netslices] Reliability & Availability in NetSling
>
> From a tenant's perspective, which arguably is the most important 
> perspective the key characteristics of interest is  surely "The Mean 
> Time Between Failures (MTBF) to maintain a defined QOS requirement." 
> together with the duration of those periods.
>
> With that information you can the viability of your application over 
> the slice, and the impact on your business.
>
> - Stewart
>
> On 11/08/2017 08:47, qiangli (D) wrote:
>
>     Hi All,
>
>     The phrase “working as expected” inspired me. For a network slice,
>     what people expect is not only the stable working
>     probability/time, but also the guaranteed SLA.
>
>     Try to consider from tenant’s perspective, I would be very
>     concerned about how much the promised SLA could really be
>     achieved. I am not sure which one (availability/reliability) this
>     concept should belong to according to ITU’s definitions.
>
>     Best regards,
>
>     Cristina QIANG
>
>     *From:*Netslices [mailto:netslices-bounces@ietf.org] *On Behalf Of
>     *Stewart Bryant
>     *Sent:* Thursday, August 10, 2017 5:58 PM
>     *To:* netslices@ietf.org <mailto:netslices@ietf.org>
>     *Subject:* Re: [Netslices] Reliability & Availability in NetSling
>
>
>     In general at IETF we associate reliable with the probability of
>     packet delivery, and a reliable transport protocol is one that
>     retries (at a cost of delay) until the packet is delivered or
>     other factors intervene. Availability tends to refer to the
>     ability of the network to receive packets for attempted delivery.
>
>     I looked for a formal definition in IPPM which is the WG that is
>     concerned with measuring such things but could not find a definition.
>
>     From the ITU we can find:
>
>     *Term* : availability (performance)
>
>     *Definition* : The ability of an item to be in a state to perform
>     a required function under given conditions at a given instant of
>     time or over a given time interval, assuming that the required
>     external resources are provided.
>     NOTE 1 –This ability depends on the combined aspects of the
>     reliability performance, the maintainability performance and the
>     maintenance support performance.
>     NOTE 2 –Required external resources, other than maintenance
>     resources do not affect the availability performance of the item.
>
>     *Term* : reliability (performance)
>
>     *Definition* : The ability of an item to perform a required
>     function under given conditions for a given time interval.
>     NOTE 1 –It is generally assumed that the item is in a state to
>     perform this required function at the beginning of the time interval.
>     NOTE 2 –Generally, reliability performance is quantified using
>     appropriate measures. In some applications, these measures include
>     an expression of reliability performance as a probability, which
>     is also called reliability.
>
>
>     or
>
>     *Term* : reliability characteristic
>
>     *Definition* : The Mean Time Between Failures (MTBF) to maintain a
>     defined QOS requirement.
>
>
>     - Stewart
>
>     On 10/08/2017 05:42, Pedro Martinez-Julia wrote:
>
>         Dear all,
>
>         I personally think it is better to use the industrial
>         definitions but,
>
>         being purist, we can find important differences between them.
>         While
>
>         availability is the probability for a system to work as
>         expected in some
>
>         period of time (99.999% of time), reliability is a broader
>         term that
>
>         refers to the different situations in which a system will be
>         able to
>
>         overcome without breaking. In some cases, the latter can
>         incorporate the
>
>         former, but not in all of them.
>
>         For network slicing we can keep the definition commonly used
>         by industry
>
>         with the necessary details to make clear the aspects that
>         differentiate
>
>         them. I would keep "working as expected for some period of
>         time" related
>
>         to availability and "resistant to disparate situations" to
>         reliability.
>
>         Regards,
>
>         Pedro
>
>         On Thu, Aug 10, 2017 at 02:44:09AM +0000, GENG Liang wrote:
>
>             Hi Cristina,
>
>             Interestingly we were discussing this confusion with few
>             industrial partners recently. In telecommunication
>             language we normally use "Reliability" to refer the
>             probability a network is stably run (i.e. 99.999% of
>             time). This is also regarded as network "Availability".
>             However, "Reliability" in industrial verticals is more
>             comprehensive - including not only network availability
>             parameter but also mechanics, electricity etc.
>
>             Personally I think, network slicing is still looking at
>             network regime where I believe Reliability means the
>             percentage of time a connection is available. But we you
>             sell this concept to industrial verticals, they may think
>             differently.
>
>             ________________________________
>
>             Liang GENG
>
>             China Mobile Research Institute
>
>             From: qiangli (D)<mailto:qiangli3@huawei.com>
>             <mailto:qiangli3@huawei.com>
>
>             Date: 2017-08-10 10:04
>
>             To: netslices@ietf.org
>             <mailto:netslices@ietf.org><mailto:netslices@ietf.org>
>             <mailto:netslices@ietf.org>
>
>             Subject: [Netslices] Reliability & Availability in NetSling
>
>             Hi All,
>
>             I was confused when I was reading some NetSlicing related
>             materials. It seems that “Reliability”supported by Netslicing refers to the probability that a
>             network slice could work stably, or other similar metrics.
>             But, shouldn’t this be the defination of “Availability”? Then what does reliability mean in NetSlicing?
>
>             Best regards,
>
>             Cristina QIANG
>
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