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>
>> Date: 2017-08-10 10:04
>> To: 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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>