[Ivy] Defining Passive: Setting out the challenge

["Davis, Nigel" <[e-mail]>]

Hi all,

On the IVY call yesterday, we discussed the challenges in defining "passive" for our passive inventory work. A few weeks ago, I constructed a brief email illustrating the challenges using a few examples. This is my second stab at this (slightly improved on my first stab that I ran through yesterday, although still very rough). During the call other examples were highlighted that further emphasized the challenge.

The text below starts with four general focusses (as I set out a few years ago in a presentation to IVY at an IETF meeting). It then continues a rough description of the focus of our work and then moves on to the challenging cases.

It is not intended that these notes fully resolve the issue. The intention is to highlight dimensions of the challenge and point towards a possible solution.

Four general focusses and relevance to our work
Some thoughts on the boundary of passive things:

  *   We had four focusses of consideration:
     *   Physical: Can be measured with a ruler (and sometime weighed with scales)
        *   This is our focus
     *   Informational: Structured data providing meaning
     *   Functional: Performs
     *   Motivational: Powers
  *   Where a physical thing augmented with information and motivated appropriately gives rise to functionality. We are not considering functionality in the passive inventory work.
  *   All physical things are motivated to be active in some way as they have some emergent function (even if it is just physically supporting something else).
  *   An informational thing is genuinely not active. We are not considering informational things in the passive inventory work.
  *   All motivating forces are essentially activity causing. We are not considering forces directly in the passive inventory work.

Our focus
To help distinguish this we need to consider our focus... which is telecommunications network services. So, functions that are core to this are in focus and hence physical things that support those functions or support the physical things that support the functions... but the importance reduces as we move out. So, we do not need to model the roadway network or the functions of a railway signalling system.

Some physical things:

  *   in the telecommunications network directly support the telecommunications functionality. These things are central to our focus. Other physical things support them. These are important but not central.
  *   are independently installable in the field (FRU) others are an inseparable part of another physical thing.
  *   need no external independent power to directly support a telecommunications function (a fibre), others need power (an integrated circuit, a laser).
  *   can be observed and others not. I can see the outside of an FRU but not necessarily see the things that comprise it.
  *   can be observed using a detector that measure a property and makes that value available to a software based system that can analyse and report the value.

Some challenging examples of things
The challenge I am seeing is that a thing may be considered passive under some circumstances and active under other circumstances.

Some examples of relevant things (some in scope some not some maybe):

  *   A fibre strand in a cable that is not lit and is not connected to anything
     *   This is a relevant inventory item from a capacity perspective. It is not monitored and is not directly detectable. It has no serial number from a manufacturing perspective but will have type properties and positioning details.
     *   It is out of use (it may even be on a drum of cable in a spares holding!)
     *   This is a classic passive item
     *   It is not individually field replaceable as it is part of a cable.
  *   A splitter that is integrated into an equipment that has power detectors on the ports of the splitter that are actively monitoring the power
     *   This is relevant inventory and is functional although does not need power other than the light itself. It is monitored
     *   This is passive but monitored (a resistor is passive)
     *   This is covered as part of an "active" equipment
     *   It is not individually field replaceable as it is part of another equipment
  *   An amplifier that is not powered and is in a spares cabinet
     *   This is relevant inventory.
     *   This is a nonmonitored active equipment that is passive because it is not powered
     *   We chose to not cover this as it is a spare
  *   An erbium doped amplifier that is powered and carrying traffic in a fully integrated solution
     *   The fibre core of the amplifier is an active element as it is pumped with a laser and is functionally an amplifier
     *   The whole amplifier is clearly active and monitored
  *   A splitter that is installed part way along a fibre span where the point of installation has no detectors
     *   This has a vital function. It does not need power separate from the signal. It is not monitored.
     *   This is a classic passive equipment
  *   A fibre span continuously monitored by an OTDR
     *   Here the fibre is not powered but it is monitored in significant detail.
     *   This would be considered as passive like any other fibre but the monitoring blurs this to a degree
  *   A fibre span used as part of a Raman amplifier
     *   This is essentially an active component, and it may be monitored by an OTDR
     *   So, here the fibre no longer seems to be passive
  *   A fire span carrying signal that has a signal fail detector in an equipment at the end
     *   Whilst the fibre is not powered other than by the signal, it is monitored to a degree.
  *   A street cabinet with a door open detector
     *   This is a passive equipment indirectly related to the signal carrying capability. It is monitored.
  *   A portacabin
     *   My contain telecoms equipment
     *   Essentially passive but out of scope as we are not covering building structures


I think we may want to apply different considerations such as

  *   Monitorable
  *   Requires power (separate from the power of the signal) to function
  *   Installed and connected
  *   Complex function
  *   Separable from another thing in the field

We should also carefully separate the functionality from the physical model. An amplifier as a physical item and as a function are two different models. As a physical item it is no different from any other equipment, that it is an amplifier is not relevant from a physical consideration. As a function, it has TPs etc.

Likewise we can then view a fibre as an equipment and take a functional view of it separately.

Our work could then focus on dealing with physical things that are long, not monitored, are structural etc. These are covered by the work under heading of passive even though they are not all passive in a "classical" sense.

Thoughts??

Nigel