Internet DRAFT - draft-quittek-eman-reference-model
draft-quittek-eman-reference-model
Network Working Group J. Quittek
Internet-Draft NEC Europe Ltd.
Intended status: Informational B. Nordman
Expires: May 3, 2012 Lawrence Berkeley National
Laboratory
R. Winter
NEC Europe Ltd.
October 31, 2011
Reference Model for Energy Management
draft-quittek-eman-reference-model-03
Abstract
Managing energy consumption of devices is different from several well
understood network management functions because of the special nature
of energy supply and use. This document explains issues of energy
management arising from its special nature and proposes a layered
reference model for energy management addressing these issues.
Status of this Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Energy Management Issues . . . . . . . . . . . . . . . . . . . 5
2.1. Power Supply . . . . . . . . . . . . . . . . . . . . . . . 6
2.1.1. Identification of Power Supply and Powered Devices . . 8
2.1.2. Multiple Devices Supplied by a Single Power Line . . . 8
2.1.3. Multiple Power Supply for a Single Powered Device . . 9
2.1.4. Relevance of Power Supply Issues . . . . . . . . . . . 10
2.1.5. Remote Power Supply Control . . . . . . . . . . . . . 10
2.2. Power and Energy Measurement . . . . . . . . . . . . . . . 11
2.2.1. Local Estimates . . . . . . . . . . . . . . . . . . . 11
2.2.2. Management System Estimates . . . . . . . . . . . . . 11
2.3. Reporting Sleep and Off States . . . . . . . . . . . . . . 11
2.4. Entities . . . . . . . . . . . . . . . . . . . . . . . . . 12
3. Energy Management Reference Model . . . . . . . . . . . . . . 12
3.1. Power Supply and Use (PSU) Layer . . . . . . . . . . . . . 13
3.1.1. Components of the PSU Layer . . . . . . . . . . . . . 14
3.1.2. Power Supply Topology . . . . . . . . . . . . . . . . 15
3.1.3. Power Sources . . . . . . . . . . . . . . . . . . . . 17
3.1.4. Power Meters . . . . . . . . . . . . . . . . . . . . . 18
3.1.5. External Power Meters . . . . . . . . . . . . . . . . 19
3.1.6. PSU Layer Relationships . . . . . . . . . . . . . . . 19
3.1.6.1. Power Source Relationship . . . . . . . . . . . . 20
3.1.6.2. Power Meter Relationship . . . . . . . . . . . . . 20
3.1.7. PSU Layer Information Model . . . . . . . . . . . . . 21
3.2. Local Energy Management Interface (LMI) Layer . . . . . . 21
3.3. Energy Management Mediation (EMM) Layer . . . . . . . . . 22
3.3.1. Remote PE Information . . . . . . . . . . . . . . . . 24
3.3.2. Remote PE Control . . . . . . . . . . . . . . . . . . 25
3.3.3. Parent function: All Available Information on a PE . . 25
3.3.4. All Available Control Affecting a PE . . . . . . . . . 26
3.3.5. Aggregated Information from Multiple PEs . . . . . . . 26
3.3.6. Aggregated Control of Multiple PEs . . . . . . . . . . 27
3.3.7. Proxying for an EO . . . . . . . . . . . . . . . . . . 27
3.4. Energy Management System Interface (EnMS) Layer . . . . . 27
4. Security Considerations . . . . . . . . . . . . . . . . . . . 27
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27
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6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 27
7. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 27
7.1. Devices or entities? . . . . . . . . . . . . . . . . . . . 28
7.2. Add PM monitoring and control interfaces to LMI layer? . . 28
7.3. Topology changes . . . . . . . . . . . . . . . . . . . . . 28
7.4. Topology reporting . . . . . . . . . . . . . . . . . . . . 28
7.5. Proxying . . . . . . . . . . . . . . . . . . . . . . . . . 28
7.6. PSU Info Model . . . . . . . . . . . . . . . . . . . . . . 28
8. Informative References . . . . . . . . . . . . . . . . . . . . 28
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29
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1. Introduction
Managing energy consumption of devices is different from several well
understood network management functions because of the special nature
of energy supply and use. This memo explains issues of energy
management arising from its special nature and proposes a reference
model for energy management addressing these issues.
Defining a suitable reference model for energy management has proven
to be explorative work that cannot be done in a single step because
the area is rather new to people at the IETF. Ideas for a reference
model have been elaborated in [I-D.ietf-eman-framework] and previous
versions of this draft.
This revision is an attempt to combine the relationship model
proposed in the last version (-02) of [I-D.ietf-eman-framework] with
the concept of power interfaces proposed in the previous version
(-02) of this draft. The result is a four layer model of energy
management.
This draft starts with identifying and describing in Section 2 the
special issues of energy management that require the development of a
new reference model. The issues concern power supply, power and
energy metering, and the reporting of low-power states.
Section 3 addresses these issues and proposed a new four layer model
for energy management, see Figure 1.
+----------------------------------------------+
| energy management system (EnMS) |
+----------------------------------------------+
||| |||
+---------------------+ |||
| energy management | |||
| mediation (EMM) | |||
+---------------------+ |||
|| |||
+----------------------------------------------+
| local energy management interface (LMI) |
+----------------------------------------------+
|
+----------------------------------------------+
| power supply and use (PSU) |
+----------------------------------------------+
Figure 1: Layers of the Energy Management Reference Model
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o Power supply and use (PSU) layer
At the lowest layer electrical objects are physically connected by
power supply lines, and these connections constitute an electric
supply topology.
o Local energy management interface (LMI) layer
This layer provides access to local information and to local
control functions at managed electrical devices.
o Energy management mediation (EMM) layer
At this layer management functions use topology information from
the PSU layer to infer information on remote devices and to
realize control functions for remote devices.
o Energy management system layer
This layer contains a centralized or distributed energy management
system that manages powered devices.
All communication with the energy management system (drawn with three
parallel lines) in Figure 1 is subject of standardization in the EMAN
working group. Communication between the EMM layer and the LMI layer
(drawn with two parallel lines) is an application area of standards
developed in the EMAN WG, but here also proprietary protocols may be
used. Communication between the LMI layer and the PSU layer (drawn
with a single line) is not subject of standardization by EMAN.
At the core of this framework are just a few key concepts. Energy is
used by Powered Devices, some of which supply power to other devices
and so are a subset called a Power Supply. Devices have power
interfaces, which are like network interfaces, through which power is
transferred into (an "inlet") or out of (an "outlet") a device.
Measurement occurs at interfaces so that the total or net consumption
of a device can be determined.
2. Energy Management Issues
This section explains special issues of energy management
particularly concerning power supply, power and energy metering, and
the reporting of low-power states.
To illustrate the issues we start with a simple and basic scenario
with a single powered device that consumes energy and that reports
energy-related information about itself to an energy management
system, see Figure 2.
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+--------------------------+
| energy management system |
+--------------------------+
^ ^
monitoring | | control
v v
+-----------------+
| powered device |
+-----------------+
Figure 2: Basic energy management scenario
The device may have local energy control mechanisms, for example
putting itself into a sleep mode when appropriate, and it may receive
energy control commands for similar purposes from a management
system. Information reported from a powered device to the energy
management system includes at least the power state of the device
(on, sleep, off, etc.).
This and similar cases are well understood and likely to become very
common for energy management. They can be handled with well
established and standardized management procedures. The only missing
components today are standardized information and data models for
reporting and configuration, such as, for example, energy-specific
MIB modules [RFC2578] and YANG modules [RFC6020].
However, the nature of energy supply and use introduces some issues
that are special to energy management. The following subsections
address these issues and illustrate them by extending the basic
scenario in Figure 2.
2.1. Power Supply
A powered device may supply itself with power. Sensors, for example,
commonly have batteries or harvest energy. However, most powered
devices that are managed by an energy management system receive
external power.
While a huge number of devices receive power from unmanaged supply
systems, the number of manageable power supply devices is increasing.
In datacenters, many Power Distribution Units (PDUs) allow the
network management system to switch power individually for each
socket and also to measure the provided power. Here there is a big
difference to many other network management tasks: In such and
similar cases, switching power supply for a powered device or
monitoring its power is not done by communicating with the actual
powered device, but with an external power supply device (which may
be an external power meter).
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Consequently, a standard for energy management must not just cover
the powered devices that provide services for users, but also the
power supply devices (which are powered devices as well) that monitor
or control the power supply for other powered devices.
A very simple device such as a plain light bulb can be switched on or
off only by switching its power supply. More complex devices may
have the ability to switch off themselves or to bring themselves to
states in which they consume very little power. For these devices as
well it is desirable to monitor and control their power supply.
This extends our basic scenario from Figure 2 by a power supply
device, see Figure 3.
+-----------------------------------------+
| energy management system |
+-----------------------------------------+
^ ^ ^ ^
monitoring | | control monitoring | | control
v v v v
+--------------+ +-----------------+
| power supply |########| powered device |
+--------------+ +-----------------+
######## power supply line
Figure 3: Power Supply
The power supply device can be as simple as a plain power switch. It
may offer interfaces to the energy management system to monitor and
to control the status of its power outlets, as with PDUs and Power
over Ethernet (PoE) [IEEE-802.3at] switches.
The relationship between supply devices and the powered devices they
serve creates several problems for managing power supply:
o Identification of corresponding devices
* A given powered device may be need to identify the supplying
power supply device.
* A given power supply device may need to identify the
corresponding supplied powered device(s).
o Aggregation of monitoring and control for multiple powered devices
* A power supply device may supply multiple powered devices with
a single power supply line.
o Coordination of power control for devices with multiple power
inlets
* A powered device may receive power via multiple power lines
controlled by the same or different power supply devices.
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2.1.1. Identification of Power Supply and Powered Devices
When a power supply device controls or monitors power supply at one
of its power outlets, the effect on other devices is not always clear
without knowledge about wiring of power lines. The same holds for
monitoring. The power supplying device can report that a particular
socket is powered, and it may even be able to measure power and
conclude that there is a consumer drawing power at that socket, but
it may not know which powered device receives the provided power.
In many cases it is obvious which other device is supplied by a
certain outlet, but this always requires additional (reliable)
information about power line wiring. Without knowing which device(s)
are powered via a certain outlet, monitoring data are of limited
value and switching on the consequences of switching power on or off
may be hard to predict.
Even in well organized operations, powered devices' power lines get
plugged into the wrong socket, or wiring plans are changed without
updating the energy management system accordingly.
For reliable monitoring and control of power supply devices,
additional information is needed to identify the device(s) that
receive power provided at a particular monitored and controlled
socket.
This problem also occurs in the opposite direction. If power supply
control or monitoring for a certain device is needed, then the
supplying power supply device has to be identified.
To conduct energy management tasks for both power supply devices and
other powered devices, sufficiently unique identities are needed, and
knowledge of their power supply relationship is required.
2.1.2. Multiple Devices Supplied by a Single Power Line
The second fundamental problem is the aggregation of monitoring and
control that occurs when multiple powered devices are supplied by a
single power supply line. It is often required that the energy
management system has the full list of powered devices connected to a
single outlet as in Figure 4.
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+---------------------------------------+
| energy management system |
+---------------------------------------+
^ ^ ^ ^
monitoring | | control monitoring | | control
v v v v
+--------+ +------------------+
| power |########| powered device 1 |
| supply | # +------------------+-+
+--------+ #######| powered device 2 |
# +------------------+-+
#######| powered device 3 |
+------------------+
Figure 4: Multiple Powered Devices Supplied by Single Power Line
With this list, the single status value has clear meaning and is the
sum of all powered devices. Control functions are limited by the
fact that supply for the concerned devices can only be switched on or
off for all of them at once. Individual control at the supply is not
possible.
If the full list of powered devices powered by a single supply line
is not known for the controlling power supply device, then control of
power supply is problematic, because the consequences of control
actions can only be partially known.
2.1.3. Multiple Power Supply for a Single Powered Device
The third problem arises from the fact that there are devices with
multiple power supplies. Some have this for redundancy of power
supply, some for just making internal power converters (for example,
from AC mains power to DC internal power) redundant, and some because
the capacity of a single supply line is insufficient.
+----------------------------------------------+
| energy management system |
+----------------------------------------------+
^ ^ ^ ^ ^ ^
mon. | | ctrl. mon. | | ctrl. mon. | | ctrl.
v v v v v v
+----------+ +----------+ +----------+
| power |######| powered |######| power |
| supply 1 |######| device | | supply 2 |
+----------+ +----------+ +----------+
Figure 5: Multiple Power Supply for Single Powered Device
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The example in Figure 5 does not necessarily show a real world
scenario, but it shows the two cases to consider:
o multiple power supply lines between a single power supply device
and a powered device
o different power supply devices supplying a single powered device
In any such case there may be a need to identify the supplying power
supply device individually for each power inlet of a powered device.
Without this information, monitoring and control of power supply for
the powered device may be limited.
2.1.4. Relevance of Power Supply Issues
In some scenarios, the problems with power supply do not exist or can
be sufficiently solved. With Power over Ethernet (PoE)
[IEEE-802.3at] there is always a one-to-one relationship between a
Power Sourcing Equipment (PSE) and a Powered Device (PD). Also, the
Ethernet link on the line used for powering can be used to identify
the two connected devices.
For supply of AC mains power, the three problems described above
cannot be solved in general. There is no commonly available protocol
or automatic mechanism for identifying endpoints of a power line.
And, AC power lines support supplying multiple powered devices with a
single line and commonly do.
2.1.5. Remote Power Supply Control
There are three ways for an energy management system to change the
power state of a managed entity. First is for a management system to
provide policy or other useful information (like the electricity
price) to the powered device for it to use in determining its power
state. The second is sending the entity a command to switch to
another state. The third is to utilize an upstream device (to the
powered device) that has capabilities to switch on and off power at
its outlet.
Some entities do not have capabilities for receiving commands or
changing their power states by themselves. Such devices may be
controlled by switching on and off the power supply for them and so
have particular need for the third method.
In Figure 3 the power supply can switch on and off power at its power
outlet and thereby switch on and off power supply for the connected
powered device.
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2.2. Power and Energy Measurement
Some devices include hardware to directly measure their power and
energy consumption. However, most common networked devices do not
provide an interface that gives access to energy and power
measurements for the device. Hardware instrumentation for this kind
of measurements is typically not in place and adding it incurs an
additional cost.
With the increasing cost of energy and the growing importance of
energy monitoring, it is expected that in future more devices will
include instrumentation for power and energy measurements, but this
may take quite some time.
2.2.1. Local Estimates
One solution to this problem is for the device to estimate its own
power and consumed energy. For many energy management tasks, getting
an estimate is much better than not getting any information at all.
Estimates can be based on actual measured activity level of a device
or it can just depend on the power state (on, sleep, off, etc.).
The advantage of estimates is that they can be realized locally and
with much lower cost than hardware instrumentation. Local estimates
can be dealt with in traditional ways. They don't need an extension
of the basic example above. However, the powered device needs an
energy model of itself to make estimates.
2.2.2. Management System Estimates
Another approach to the lack of instrumentation is estimation by the
energy management system. The management system can estimate power
based on basic information on the powered device, such as the type of
device, or also its brand/model and functional characteristics.
Energy estimates can combine the typical power level by power state
with reported data about the power state.
If the energy management system has a detailed energy model of the
device, it can produce better estimates including the actual power
state and actual activity level of the device. Such information can
be obtained by monitoring the device with conventional means of
performance monitoring.
2.3. Reporting Sleep and Off States
Low power modes pose special challenges for energy reporting because
they may preclude a device from listening to and responding to
network requests. Devices may still be able to reliably track energy
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use in these modes, as power levels are usually static and internal
clocks can track elapsed time in these modes.
Some devices do have out-of-band or proxy abilities to respond to
network requests in low-power modes. Others could use proxy
abilities in an energy management protocol to improve this reporting,
particularly if the device sends out notifications of power state
changes.
2.4. Entities
The primary focus of energy management is entire devices, but in some
applications it is necessary or desirable to also have visibility
into energy use of internal components such as line cards, fans,
disks, etc. Components lack some of the features of devices, such as
having power interfaces; instead, they simply have a net total
consumption from the pool of power available within a device. Note
that a device need not have an AC power cord. For example, a DC-
powered blade server in a chassis has its own identity on the network
and reports for itself, and so is a separate device, not a component
of the chassis.
3. Energy Management Reference Model
This section specifies a reference model for energy monitoring and
explains how it solves the problems outlined above. It is structured
into four layers:
+----------------------------------------------+
| energy management system (EnMS) |
+----------------------------------------------+
||| |||
+---------------------+ |||
| energy management | |||
| mediation (EMM) | |||
+---------------------+ |||
|| |||
+----------------------------------------------+
| local energy management interface (LMI) |
+----------------------------------------------+
|
+----------------------------------------------+
| power supply and use (PSU) |
+----------------------------------------------+
Figure 6: Layers of the Energy Management Reference Model
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At the power supply and use (PSU) layer electrical objects (powered
entities) are physically connected by power supply lines. Their
connections constitute an electric supply and metering topology.
The local energy management interface (LMI) layer provides a set of
functions for monitoring and controlling individual powered entities.
These functions are local to the entity and restricted to only report
properties and states of the entity, as with most common network
management functions on managed entities today.
The energy management mediation (EMM) layer provides 'convenience'
functions to the energy management system. It performs functions
specific to energy management by utilizing information from the PSU
layer to infer information on Electrical Objects (EOs) and to bundle
control functions concerning the same EO. It also offers some more
general functions such as proxying and aggregation on monitored
information.
The energy management system (EnMS) layer contains a centralized or
distributed energy management system that manages a set of powered
devices.
3.1. Power Supply and Use (PSU) Layer
This layer models the electrical connections between electrical
objects. "Electrical object" (EO) is used as general term for three
kinds of objects. An EO is a powered entity (PE). Connections
between them are made with power supply lines.
According to the general issues identified in Section 2.1 the
following specific issues are addressed at this layer:
o Identification of electrical connection endpoints
o Supply relationships between connected EOs
o Aggregation of power supply for multiple PEs
o Metering at connection endpoints
o Metering relationships between connected EOs
o Aggregation of metering for multiple PEs
For the general problem of identifying EOs, there are many methods
already in use by network management systems. Such methods include
identification by IP addresses, by MAC addresses, by serial numbers,
by assigned UUIDs, etc. Those can be re-used for identifying EOs.
There does not yet exist a commonly used way to address different
power interfaces of the same device. There are power distribution
units that enumerate their power outlets and Power over Ethernet
switches that enumerate their ports and port groups.
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The reference model for the PSU layer uses the concept of a power
interface to address the identification of individual connection
endpoints of power supply lines at EOs.
This term is not new. It is already used similarly by the IEEE
standard for Power over Ethernet (PoE) [IEEE-802.3af] and
[IEEE-802.3at] where a power interface denotes the interface between
a device and the Ethernet transmission medium. The following terms
for components of the PSU layer are derived from PoE terminology.
3.1.1. Components of the PSU Layer
o Power Interface (PI)
A power interface is the interface between an EO and a power
transmission medium. There are some similarities between power
interfaces and network interfaces. A network interface can be
used in different modes, such as sending or receiving on an
attached line. A power interface (PI) has an attribute indicating
its mode that can be one of the following:
* inlet: receiving power
* outlet: providing power
Most power interfaces never change their mode, but as the mode is
simply a recognition of the current direction of electricity flow,
there is no barrier to a mode change.
A power interface can have capabilities for metering power and
other electric quantities at the shared power transmission medium.
This capability it modeled by an association to a power meter.
In analogy to MAC addresses of network interfaces, a globally
unique identifier is assigned to each power interface.
Physically, a power interface can be located at an AC power
socket, an AC power cord attached to a device, an 8P8C (RJ45) PoE
socket, etc.
o Powered Entity (PE)
An entity which consumes or supplies power with one or more PIs in
mode "inlet" is called a powered entity (PE). This extends the
term powered device (PD) used in [IEEE-802.3af] and [IEEE-802.3at]
to cover not only entities that are individual devices, but also
entities that are just components of devices.
o Power Source (PS)
An entity with one or more PIs in mode "outlet" is called a power
source (PS). This extends the term Power Source Equipment (PSE)
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used in the IEEE PoE standards [IEEE-802.3af] and [IEEE-802.3at]
where at a single PI the PSE provides power to a single PD only.
Here a PS may supply an arbitrary number of PEs at a single PI.
Most PSs have also PIs in mode "inlet" and all are also a PE.
o Power Meter (PM)
A metering function attached to a power interface of an entity is
called a power meter (PM). Power meters are contained within an
entity and attached to one or more of the entity's power
interfaces. A single PM can only provide a single meter reading
at a time. Most PIs will be connected to a single other PI only,
but those attached to multiple power interfaces only measure the
aggregate use over all of the other interfaces. Components that
lack interfaces have a meter for their total net consumption.
3.1.2. Power Supply Topology
Similar to network interfaces, power interfaces can be connected to
each other via a shared (power) transmission medium. The most simple
connection is a single outlet connected to a single inlet as shown in
Figure 7.
+----------------+ +----------------+
| power source | | powered entity |
| +----------+ | | +----------+ |
| | PI, ID 1 ########## PI, ID 2 | |
| | (outlet) | | | | (inlet, | |
| | | | | | meter) | |
| +----------+ | | +----------+ |
+----------------+ +----------------+
Figure 7: Simple one-to-one power supply topology
This figure extends the PSU layer of Figure 3 by power interfaces.
The power source has a single power interface in outlet mode
connected to a power supply lime that connects it to the power
interface of the powered entity in inlet mode. The corresponding PSU
layer model of the topology in Figure 7 is shown by Figure 8.
PS ----- PI ID 1 ----- PI ID 2 ----- PE
outlet inlet
|
|
PM
Figure 8: PSU layer model for one-to-one supply topology
This model shows four relationships,
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o a containment relationship modeling the power source PS containing
the power interface PI with ID 1,
o a containment relationship modeling the powered entity PE
containing the power interface PI with ID 2,
o a metering relationship between PI ID 2 and a power meter PM.
o a connection relation between PI ID 1 and PI ID 2.
Implicit in this model is a containment relationship between the PE
and the PM. It is implicit, because the PI ID 2 is contained in the
PE and the PI ID 2 has a metering relationship with the PM.
The model also shows that PIs have an attribute indicating the mode.
In Figure 8 PI ID 1 is in mode "outlet" and PI ID 2 is in mode
"inlet".
Figure 9 extends the PSU layer of the example from Figure 4 by power
interfaces. A power source with a single outlet supplies three
powered entities.
+----------------+ +------------------+
| power source | | powered entity I |
| +----------+ | | +----------+ |
| | PI, ID 3 ############## PI, ID 4 | |
| | (outlet) | | # | | (inlet) | |
| +----------+ | # | +----------+ |----+
+----------------+ # +------------------+ II |
# | +----------+ |
########## PI, ID 5 | |
# | | (inlet) | |
# | +----------+ |-----+
# +---------------------+ III |
# | +----------+ |
########## PI, ID 6 | |
| | (inlet) | |
| +----------+ |
+-------------------------+
Figure 9: PSU Layer for a Single PS Supplying Multiple PEs.
The corresponding PSU layer data model is shown by Figure 10.
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PS ----- PI ID 3 --+-- PI ID 4 ----- PE I
outlet | inlet
|
+-- PI ID 5 ----- PE II
| inlet
|
+-- PI ID 6 ----- PE III
inlet
Figure 10: PSU Layer Model of a Single PS Supplying Multiple PEs.
Figure 11 shows the PSU layer model of the example from Figure 4. A
PE with three inlets is supplied by two power sources PS I and PS II.
There are two power supply connections between PS I and the PE.
PS I --+-- PI ID 7 ----- PI ID 8 --+-- PE
| outlet inlet |
| |
+-- PI ID 9 ----- PI ID 10 --+
outlet inlet |
|
PS II ----- PI ID 11 ----- PI ID 12 --+
outlet inlet
Figure 11: Multiple Power Supply for Single Powered Device
3.1.3. Power Sources
In the PSU layer, a EO that is a power supply can be seen as having
two roles in that it is also a PE. A good example is a PoE switch
that is a PE supplied with AC power and a PS supplying other PEs with
DC power. Examples which are pure AC devices include a UPS or a PDU.
+--------------------------------------------------------+
| powered entity / power source |
| +---------+ +---------+ +---------+ +---------+ |
###### PI ID 13| | PI ID 14| | PI ID 15| | PI ID 16| |
| | (inlet) | | (outlet)| | (outlet)| | (outlet)| |
| +---------+ +----#----+ +----#----+ +----#----+ |
+----------------------#------------#------------#-------+
# # #
Figure 12: Power Source Roles
Figure 12 shows the example a power source with three power outlets
and a power inlet and Figure 13 shows its PSU layer information
model.
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EO -------+------------+------------+------------+
PE | | | |
PS PI ID 13 PI ID 14 PI ID 15 PI ID 16
inlet outlet outlet outlet
Figure 13: PSU Layer Model of a Dual Role Power Source
3.1.4. Power Meters
On the PSU layer each power and energy meter is integrated with one
or more power interfaces, though usually just with one, or with a
component. A common case is shown by Figures 7 and 8 where the PE
has metering capability at its power inlet. Power outlets can have
metering capabilities as well.
When power meters are attached to more than one power interface
within a single powered entity, the PM cannot report per power
interface individually, but just the summed of multiple interfaces.
A common example is a PoE switch that measures power per group of
eight ports. Another example is a powered entity with two power
inlets that only measures the total power input to the entity as
illustrated by Figure 14 and modeled by Figure 15.
+--------------+ +--------------+
| power | +--------------------------+ | power |
| source 1 | | powered entity | | source 2 |
| +---------+ | | +---------+ +---------+ | | +---------+ |
| | PI ID 17########## PI ID 18| | PI ID 19########## PI ID 20| |
| | (outlet)| | | | (inlet) | | (inlet) | | | | (outlet)| |
| +---------+ | | +----#----+ +----#----+ | | +---------+ |
+--------------+ | # # | +--------------+
| +----#------------#----+ |
| | power meter | |
| +----------------------+ |
+--------------------------+
Figure 14: Dual power supply topology
PS I ----- PI ID 17 ----- PI ID 18 --+-- PE
outlet inlet |
| |
| |
PM |
| |
| |
PS II ----- PI ID 19 ----- PI ID 20 --+
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Figure 15: PSU Layer Model of a Dual Role Power Source
A power meter can cover any mixture of inlets and outlets and simply
reports the sum. As an example, see the model of a the dual role PE
and PS from Figure 13 extended by a power meter attached to all PIs
in Figure 16.
EO -------+------------+------------+------------+
PE | | | |
PS PI ID 13 PI ID 14 PI ID 15 PI ID 16
inlet outlet outlet outlet
| | | |
+------------+------------+------------+----- PM
Figure 16: PSU Layer Model of a Dual Role Power Source
3.1.5. External Power Meters
A device which is only a power meter is modeled exactly as any other
PS. It is modeled as a device that has an inlet power interface
receiving power from a PS and one or more outlet power interfaces
providing power to PEs, see, for example, Figure 17. The fact that a
device may consume none of the energy that passes through it is not
relevant to EMAN.
+------------------------------+
| external power meter |
| +---------+ +---------+ |
from PS ###### PI ID 21| | PI ID 22###### to PE(s)
| | (inlet) | | (outlet,| |
| | | | meter) | |
| +---------+ +---------+ |
+------------------------------+
Figure 17: External Power Meter
3.1.6. PSU Layer Relationships
The PSU topology is usually asymmetric. PS devices supply other PEs
with power and meters may measure power that is consumed or provided
by other entities than the one at which the measurement was
conducted. This way we define two kinds of relationships between EOs
in the PSU layer: power source relationships and power meter
relationships
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3.1.6.1. Power Source Relationship
A power source relationship exists between an outlet PI of a PS and
an inlet PI of a PE. It is an asymmetric relationship. The role of
the outlet is providing energy and the role of the inlet is receiving
energy.
An outlet can be directly connected to multiple inlets and thus can
have multiple power source relationships. An inlet is typically
connected to a single outlets only and thus has only one power source
relationship to a directly connected outlet. While not common, an
inlet can be connected to multiple outlets.
The relationship is transitive. If an outlet PI acts as power source
for an inlet PI of an entity that itself acts as PS for further PEs,
then the outlet may have also power source relationships to inlets of
entities supplied by the entity in the middle.
Figure 18 shows a simple example. PI ID 23 has a power source
relationship with PI Id 24. But since the entity in the middle is a
dual role device that also acts as PS, PI ID 23 has also a power
source relationship with PI ID 26.
PS 1 PE 1 / PS 2 PE 2
| | |
| +-----+------+ |
| | | |
PI ID 23 ----- PI ID 24 PI ID 25 ----- PI ID 26
outlet inlet outlet inlet
| |
PM PM
Figure 18: Relationships between Cascaded Power Sources
3.1.6.2. Power Meter Relationship
The power meter relationship is very similar to the power source
relationship. It is asymmetric as well and it has two roles: the
metering PI and the metered PI. Different from the power source
relationship, the role of a PI does not depend on its mode. The
metering PI can be an outlet PI or an inlet PI. The same holds for
the metering PI. Thus this relationship works not just downstream
but also upstream.
In Figure 18 PI ID 23 has a metering relationship as metering PI with
PI ID 24 in the downstream direction. In the same way, PI ID 26 is
the metering PI in a metering relationship with PI ID 25. Assuming
that PE 1 / PS 2 is just a switch with no energy consumption, PI ID
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23 and PI ID 26 have two metering relationship with each other with
different directions. In one PI IS 23 measures power remotely for PI
ID 26 and in the other one measured value at PI ID 26 can be used to
report the power at PI ID 23.
3.1.7. PSU Layer Information Model
Figure 19 illustrates the information model of the PSU layer.
Electrical objects (EOs) are a synony for powered entity.
+--------------------+ 1 +-----------+ 1..N +-------+
+->| electrical |--------| power |--------| power |
| | object | 0..N | interface | 0..N | meter |
| +--------------------+ +-----------+ +-------+
| | ID |
| +--------------------+ | mode |
+--| powered entity | +-----------+
+--------------------+ 0..N | | 0..N
+---+
Figure 19: Basic Information Model of the PSU Layer
Each EO contains a number of PIs. PIs have two attributes, their ID
and their mode. Each PI may be attached to one or more PMs. A PM
may be attached to one or more PIs. Finally, a PI may be connected
to one or more PIs of other EOs.
3.2. Local Energy Management Interface (LMI) Layer
The local energy management interface (LMI) layer provides a set of
interfaces for monitoring and controlling power and use of energy at
EOs. These interfaces are offered by an EO and restricted to only
report and control properties and states that are local to the EO, as
do most of the common network management interfaces at managed
entities today.
Interfaces at this layer deal components of the PSU layer at the
local EO. They are structured into five specific interfaces:
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^ ^ ^ ^ ^
| | | | |
+------------------------------------------------------------------+
| EO | | | | | |
| v v v v v |
| +----------+ +----------+ +----------+ +----------+ +----------+ |
| | PI | | PI | | meter | | power | | power | |
| |monitoring| | control | | reading | | state | | state | |
| | | | | | | |monitoring| | control | |
| +----------+ +----------+ +----------+ +----------+ +----------+ |
+------------------------------------------------------------------+
Figure 20: Interfaces of an EO at the LMI layer
o PI monitoring
This interfaces provide methods for retrieving information on PIs
contained in the EO. Particularly included is information on the
mode of the PI (inlet or outlet) and its operational state (on,
off, ready, etc.) and known power source relationships and power
meter relationships.
o PI control
PI control is limited to switching PIs on and off.
o Meter reading
This interfaces includes methods for reporting quantities that are
measured by power meters and that are related to power and to
energy consumption.
o Power state monitoring
Methods of this interface provide information on power states of
PEs. These methods are only available at PEs. But since all EOs
can be considered to be PEs they can in general be made available
at any EO.
o Power state control
The number of control methods at this interface may be very small.
At least included is a method for setting the power state of a PE.
3.3. Energy Management Mediation (EMM) Layer
Information and control means provided by the LMI layer is local to
the reporting EO. However, with information from the PSU layer,
there are some obvious steps of processing this information to make
it more useful or easier to digest by an energy management system.
In general, all functions in this layer are 'convenience' functions
and an energy management system can execute all of them directly.
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This layer may contain various kinds of functions. The ones that are
already known can be structured into 7 groups:
o remote PE information
o remote PE control
o all available information on a PE
o all available control affecting a PE
o aggregated information from multiple PEs
o aggregated control of multiple PEs
o proxying for an EO
This list may not be complete, so that new 'convenience' functions
may be added. Some of them may not match any of the groups listed
above. Figure 21 shows (except for the proxying functions) how the
groups are structured in the EMM layer and interact with the LMI
layer.
+---------------------------------------------------------------+
| energy management system |
+---------------------------------------------------------------+
^ ^ ^ ^ ^ ^ ^
| | | | | | |
v | | | | | v
+------------------+ | | | | | +------------------+
| aggregated | | | | | | | aggregated |
| info on | | | | | | | control of |
| multiple PEs | | | | | | | multiple PEs |
+------------------+ | | | | | +------------------+
| | | | | | | | | | |
| | v v | | | v v | |
| | +-------------+ | | | +-------------+ | |
| | | all info | | | | | all control | | |
| | | on a PE | | | | | of a PE | | |
| | +-------------+ | | | +-------------+ | |
| | | | | | | | | | |
| +---------+ | | | | | +---------+ |
| | v v v | v v v | |
| | +-------------+ | +-------------+ | |
| | | remote PE | | | remote PE | | |
| | | information | | | control | | |
| | +-------------+ | +-------------+ | |
| | | | | | |
v v v v v v v
+----------------------------------------------------------------+
| LMI layer |
+----------------------------------------------------------------+
Figure 21: Groups of Functions in the LMI layer
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In this layer, EOs offer functions to the EnMS that concern other
PEs. By doing so, they establish a relationship to the respective
PEs. Relationships on this layer include
o Reporting relationship
This relationship is between a reporting EO and a PE on which it
reports. It is an asymmetric relationship and the PE on which is
reported may not even have any knowledge on the existence of the
relationship. Subject of reporting can be the power supply status
for PE, metered values for a PE, a power state information on a
PE, and other information on the PE that is relevant for the
energy management system.
o Control relationship
Analogous to the reporting relationship, the control relationship
is between a controlling EO and a controlled PE. Again, the PE
does not necessary know of this relationship, for example, in case
the controlling EO controls the power supply of a PE by
communicating with the PS supplying the PE. This can be done in a
way that is completely hidden from the PE. Subject of control can
be the power supply of the PE, its power state, and other states
relevant for the energy management system.
o Proxy relationship
This is a relationship between a proxying EO and a proxied PE.
The concept of a proxy relationship overlaps with the reporting
relationship and the control relationship. A proxy relationship
always includes one of the two or both. Characteristic for a
proxy relationship is that it includes reporting or control
function that the proxying EO cannot conduct without remotely
retrieving data or remotely controlling other EOs.
The groups of the EMM layer are described individually in the
following subsections.
3.3.1. Remote PE Information
This group contains functions that allow an EO to provide information
about another PE. These functions are useful in scenarios like the
ones described in Section 2.1 where an EO switches or measures power
at an outlet PI. If the EO has information on the PSU layer
topology, particularly about which PEs are connected to the outlet,
then it can combine this information and report on the power supply
for the connected PEs.
This way an EO uses local information and deduces information on
other, remote PEs from it. Such information may not be as reliable
as a direct report from the concerned PEs, but it is often valuable
information for energy management. Such reporting must be cognizant
of possibilities like devices with multiple power supplies.
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The functions in this group can also be implemented by EOs that are
neither one of the concerned PEs nor the EO at which the observation
or measurement was conducted. In such a case the executing EOs of
these functions act as a kind of mid-level manager between management
system and managed devices and could, for example, be components of
an conventional element management system.
Obviously, the EO that reports on a certain other PE has a reporting
relationship to the PE. However, if the PE is aware of the
relationship, the PE may have means to report which EO has which kind
of relationship to it.
Like some other functions on the EMM layer, the remote PE functions
are 'convenience' functions. Inferring available information from
different EOs can also be done by the energy management system.
3.3.2. Remote PE Control
This group has some similarities to the previous one. Again,
operations at an EO are combined with knowledge of the PSU layer
topology in order to realize operations on a remote PE. In the
example scenario from figures 7 and 8, power for the PE can be
switching by switching the outlet PI ID 1 of the PS. On the LMI
layer the offered function would be "switch of PI ID 1 at PS". This
function can be offered by the PS at the EMM layer as "switch power
for the PE". Both function would have the same technical effect, but
they are semantically on different layers.
Here, the EO that controls an PE has a control relationship to the
PE. If the PE is aware of the relationship, the PE may have means to
report which EO has which kind of relationship to it.
Again, like in the previous group, these functions are convenience
functions and they can be executed by the PS, by the PE or by any
other EO.
3.3.3. Parent function: All Available Information on a PE
This group provides just a single logical function that we call the
parent function for reporting: A parent EO makes all information on a
PE, that is available somewhere in the network, but that might be
distributed among several EOs, available at a single point of
contact, the parent.
Realizing such a function would be expected to require to instantiate
several of the functions in the "Remote PE Information" group
described above.
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The parent EO that provides all available information on a certain
other PE has definitely a reporting relationship to it. In addition
it may have a proxying relationship, for example if it reports the
PE's power state.
This function is again a 'convenience' function for an energy
management system that in some cases may be much easier done locally
at involved EOs than within the energy management system.
3.3.4. All Available Control Affecting a PE
This group also provides just a single logical function: The parent
control function: It makes all control functions affecting a PE, that
are available somewhere in the network, but that might be distributed
among several EOs, available at a single point of contact, the
parent.
Realizing such a function would be expected to require to instantiate
several of the functions in the "Remote PE Control" group described
above.
Again, the parent EO that controls a certain other PE has a control
relationship to it. If controls the power state, it may also be a
proxy relationship.
This function is again a 'convenience' function for an energy
management system that in some cases may be much easier done locally
at involved EOs than within the energy management system.
3.3.5. Aggregated Information from Multiple PEs
Functions in this group aggregate monitoring information from
multiple PEs into more compact representations with potential loss of
information.
For example, power measurements from a set of PEs may be summed up
into a single value that is provided to an energy management system
that does not need more detailed information. aggregating such
information in the EMM layer is not just a convenience functions but
may also increase scalability of the energy management system.
Aggregation is not necessarily limited to just summing up values.
Also included, for example, are aggregation functions that give
information on how many PEs of a group are in a certain power state.
The range of potential functions in this group appears to be huge.
However, it will probably sufficient to standardize the most commonly
used ones only.
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3.3.6. Aggregated Control of Multiple PEs
Like monitoring and reporting functions covered in the previous
group, also control functions can be aggregated. Examples include
switching power supply for all PEs in a given group or setting all of
them to the same power state with a single command.
Again, this can be considered a convenience function, but at the same
time increase scalability of the energy management system. And again
it will probably be sufficient to standardize just a few of the wide
range of possible functions in this group.
3.3.7. Proxying for an EO
This section still needs to be written. Summary: An EO can act as a
proxy for an EO that cannot directly communicate with the energy
management system.
3.4. Energy Management System Interface (EnMS) Layer
The EMS receives EMAN data directly from devices, or via the
mediation layer. Similarly, it can exercise control directly or via
the mediation layer. In many cases, the same action can be
accomplished through either means, though some are only available via
mediation.
4. Security Considerations
This memo currently does not impose any security considerations.
5. IANA Considerations
This memo has no actions for IANA.
6. Acknowledgements
This memo was inspired by discussions with Benoit Claise, John
Parello, Mouli Chandramouli, Rolf Winter, Thomas Dietz, Bill Mielke,
and Chris Verges.
7. Open Issues
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7.1. Devices or entities?
Entities expands on the category of devices by adding components. Do
components have all the features of devices (including having power
interfaces) or do they only have metering of their energy/power use?
The relationships among powered devices, powered entities,
components, and electrical objects needs to be clarified.
7.2. Add PM monitoring and control interfaces to LMI layer?
In earlier versions of this draft, monitoring and configuring the
power meter have also been considered. Shall we list them as further
local interfaces on the LMI layer?
7.3. Topology changes
Ideally topology would never change so the EMS need only query it
once. A date/time stamp for time of last topology change would
enable the EMS to know when it needs to rescan the topology.
7.4. Topology reporting
For each interface, there is a list of [device,interface] tuples that
is connected to the interface. If one of these is listed as
"unknown", then any number of unknown devices may be connected (that
is, the device need not specify the number, since likely it will
usually not know). Topology information need not be symmetric. A
device providing power to the second may know the ID of the second
while the second device may lack knowledge of the ID of the supplying
device. The mediation layer brings together such information to form
a more complete picture.
7.5. Proxying
Does all proxying occur at the mediation layer?
7.6. PSU Info Model
The PSU layer information model needs to be further elaborated.
8. Informative References
[RFC2578] McCloghrie, K., Ed., Perkins, D., Ed., and J.
Schoenwaelder, Ed., "Structure of Management Information
Version 2 (SMIv2)", STD 58, RFC 2578, April 1999.
[RFC6020] Bjorklund, M., "YANG - A Data Modeling Language for the
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Network Configuration Protocol (NETCONF)", RFC 6020,
October 2010.
[I-D.ietf-eman-framework]
Claise, B., Parello, J., Silver, L., and J. Quittek,
"Energy Management Framework",
draft-ietf-eman-framework-02 (work in progress),
July 2011.
[IEEE-802.3af]
IEEE 802.3 Working Group, "IEEE Std 802.3af-2003 - IEEE
Standard for Information technology - Telecommunications
and information exchange between systems - Local and
metropolitan area networks - Specific requirements - Part
3: Carrier Sense Multiple Access with Collision Detection
(CSMA/CD) Access Method and Physical Layer Specifications
- Amendment: Data Terminal Equipment (DTE) - Power via
Media Dependent Interface (MDI)", July 2003.
[IEEE-802.3at]
IEEE 802.3 Working Group, "IEEE Std 802.3at-2009 - IEEE
Standard for Information technology - Telecommunications
and information exchange between systems - Local and
metropolitan area networks - Specific requirements - Part
3: Carrier Sense Multiple Access with Collision Detection
(CSMA/CD) Access Method and Physical Layer Specifications
- Amendment: Data Terminal Equipment (DTE) - Power via
Media Dependent Interface (MDI) Enhancements",
October 2009.
Authors' Addresses
Juergen Quittek
NEC Europe Ltd.
Network Research Division
Kurfuersten-Anlage 36
Heidelberg 69115
DE
Phone: +49 6221 4342-115
Email: quittek@neclab.eu
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Bruce Nordman
Lawrence Berkeley National Laboratory
1 Cyclotron Road
Berkeley 94720
US
Phone: +1 510 486 7089
Email: bnordman@lbl.gov
Rolf Winter
NEC Europe Ltd.
Network Research Division
Kurfuersten-Anlage 36
Heidelberg 69115
DE
Phone: +49 6221 4342-121
Email: Rolf.Winter@neclab.eu
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