1. Unified Metrics for Management of Smart Grid Home Area Networks
doc.: IEEE yy/xxxxr0
Month Year
July 2010
Unified Metrics for Management of Smart Grid Home Area Networks
Date:
Authors:
Tim Godfrey, EPRI
John Doe, Some Company

2. Unified Metrics for Management of Smart Grid Home Area Networks
IEEE International Communications Conference
Smart Grid Communication Workshop
23 May 2010
Tim Godfrey Craig Rodine

3. EPRI Corporate Overview (www.epri.com)
Not-for-profit, membership org; executes research programs for US and international utilities
Annual budget ~$350Mn USD; 800 employees; 8 offices (6 US, 2 int’l); 3 laboratories (US)
100s of EPRI utility members represent >90% of electricity generated in the USA
Divisions: Generation, Nuclear, Power Delivery & Utilization, Environment, Renewable Energy, Energy Efficiency, Technology Innovation
R&D Priorities include:
Next generation nuclear, coal, and natural gas power plants
CO2 capture and storage technologies
Smart grid technologies
Cost-competitive, grid-compatible renewable generation
Reliable, long-lived power systems components and infrastructure
Efficient power system and customer electro-technologies
PHEV-compatible power delivery networks
Science to inform environmental decision-making 3

4. Home Area Network (HAN) Overview
Home Area Networks (HANs) allow electric utilities to offer energy services to their customers through a gateway or Energy Services Interface.
This function can be offered via a broadband Internet connection, or the utility AMI system via an interface on the Smart Meter.
We are studying three leading SDO-backed HAN technology families:
Zigbee (IEEE )
Homeplug AV/GP-SE (IEEE P1901)
Wi-Fi (IEEE b/g/n) 4

5. HAN Comms Reliability
AMI Systems need to support end-to-end communications for Demand Response, Pre-Pay, PEV Charging, and similar retail energy services.
Communication between devices via the Home Area Network (HAN) thus becomes a mission-critical resource for utilities and energy service providers.
Problem: there are no standardized ways to determine the status, health and performance of communications over wireless or wired HAN technologies. 5

6. Objectives for HAN Metrics
Verify at installation time that a HAN device has established reliable communications with a controller or peer.
Enable operators to check that a HAN device or controller is communicating reliably post-installation.
Establish diagnostics and metrics to help operators identify problems and minimize the HAN service burden.
Establish baseline performance metrics that are comparable across popular HAN standards – Wi-Fi, Zigbee, HomePlug.

7. PHY Layer Metrics
Link Quality – an abstract concept (dimensionless value), independent of underlying network technology
By nature, PHY metrics are per-connection.
Maintained for each peer address
Data rates and link quality are inter-related for some standards
Signal strength and background noise are other useful PHY metrics
IEEE standards provide PHY metrics as part of the PHY Data SAP, and the PLME SAP

8. Per-connection and Per-device Metrics
PHY metrics such as link quality and signal strength are per-connection. The value is associated with the connection to a peer device.
Example PHY Metrics
Metrics drop out of list w/ age
Table size implementation dependent
MAC Metrics are per-device
They represent the status of a particular device’s MAC.
Statistics are maintained for all RX and TX frames
Higher layers can track per-connection if needed

9. MAC Layer Metrics
PHY Layer metrics (Energy and Link Quality) do not give a complete picture of network performance
Errors due to periodic variation between PHY measurements times and actual times transmission and reception
The MAC works with the PHY to transfer information
Internal behavior & state represent useful information
Like PHY metrics, MAC layer metrics can be gathered passively, by monitoring the behavior of existing traffic as it is sent and received on the network
No overhead is added by gathering metrics

10. Derivation of Metrics from 802.11 (Wi-Fi)
(802.11k)
dot11TransmittedFragmentCount
dot11MulticastTransmittedFrameCount
dot11FailedCount
dot11ReceivedFragmentCount
dot11MulticastReceivedFrameCount
dot11FCSErrorCount
dot11TransmittedFrameCount
dot11RetryCount
dot11MultipleRetryCount
dot11FrameDuplicateCount
dot11RTSSuccessCount
dot11RTSFailureCount
dot11ACKFailureCount

11. Derivation of Metrics from 802.11 (Wi-Fi)
(802.11k)
dot11TransmittedFragmentCount
dot11MulticastTransmittedFrameCount
dot11FailedCount
dot11ReceivedFragmentCount
dot11MulticastReceivedFrameCount
dot11FCSErrorCount
dot11TransmittedFrameCount
dot11RetryCount
dot11MultipleRetryCount
dot11FrameDuplicateCount
dot11RTSSuccessCount
dot11RTSFailureCount
dot11ACKFailureCount

12. Derivation of Metrics from P1901 (HomePlug)
P1901 (CM_LINK_STATS)
BeaconPeriodCnt
Rx/Tx_NumMSDUs
Rx/Tx_Octets
Tx_NumSegs
Rx/Tx_NumSeg_Suc
Rx/Tx_NumSeg_Dropped
Rx/Tx_NumPBs
Rx/Tx_NumMPDUs
Tx_NumBursts
Tx_NumSACKs
Rx_NumICV_Fails
CC_BEACON_RELIABILITY
LatBin (0…n)

13. Derivation of Metrics from P1901 (HomePlug)
P1901 (CM_LINK_STATS)
BeaconPeriodCnt
Rx/Tx_NumMSDUs
Rx/Tx_Octets
Tx_NumSegs
Rx/Tx_NumSeg_Suc
Rx/Tx_NumSeg_Dropped
Rx/Tx_NumPBs
Rx/Tx_NumMPDUs
Tx_NumBursts
Tx_NumSACKs
Rx_NumICV_Fails
CC_BEACON_RELIABILITY
LatBin (0…n)

14. Metrics for (Zigbee)
The existing standard does not include MAC layer metrics.
The “philosophy” of is to keep the MAC very simple and small
Many applications require low power and low cost
The complex measurements of k and P1901 would not be acceptable.
A subset of the MAC metrics were defined to provide the best visibility of behavior for Smart Grid applications.
These metrics are included in the amendment developed by Task Group 4e

15. Derivation of Metrics from Existing Standards
Selected Subset
(dot11Counters Group and dot11MACStatistics Group
P1901
(CM_LINK_STATS.CNF group)
dot11RetryCount
LatBin (0)
dot11MultipleRetryCount
LatBin (1…n)
dot11FailedCount
Tx_NumSeg_Dropped
dot11TransmittedFrameCount
Tx_NumSeg_Suc
dot11FCSErrorCount
Rx_NumICV_Fails
dot11FrameDuplicateCount
N/A
dot11ReceivedFragmentCount
Rx/Tx_NumMSDUs

16. Derivation of Metrics from Existing Standards
Selected Subset - extended to
(dot11Counters Group and dot11MACStatistics Group
(MAC PIB Attributes)
P1901
(CM_LINK_STATS.CNF group)
dot11RetryCount
macRetryCount
LatBin (0)
dot11MultipleRetryCount
macMultipleRetryCount
LatBin (1…n)
dot11FailedCount
macTXFailCount
Tx_NumSeg_Dropped
dot11TransmittedFrameCount
macTXSuccessCount
Tx_NumSeg_Suc
dot11FCSErrorCount
macFCSErrorCount
Rx_NumICV_Fails
dot11FrameDuplicateCount
macDuplicateFrameCount
N/A
dot11ReceivedFragmentCount
macRXSuccessCount
Rx/Tx_NumMSDUs

17. Standards-Independent Metrics
A consistent set of metrics across multiple HAN standards
Simplifies central management and monitoring software
Give utilities flexibility in deploying HANs
The selected subset of MAC and PHY metrics may be adapted to new HAN standards as they are developed

18. Interpretation of Metrics - Transmit
MAC transmit metrics are primarily derived from retry and acknowledgement behavior
Represent the amount of “effort” the MAC has to make to send a packet
Retry behavior represents different types of network impairments
Good RF conditions
Weak Signal
Interference Bursts

19. Interpretation of Metrics - Receive
FCS (Frame Check Sequence) or ICV (Integrity Check Value) failure.
Typically a CRC over the frame’s data payload
A mismatch in the FCS or ICV indicates an error.
Duplicate Frames
When an ACK is not received, the sender retries the transmission.
Duplicate frame at receiver means sender did not receive the ACK
Possibly interference local to the sender
Transmit
Receive
Frame N
Lost X
ACK
Retry Frame N
Duplicate

20. Architecture for communicating metrics
Per-device statistics may be made accessible in management entity
e.g. SNMP
SNMP SET/GET
MAC metrics
MAC metrics
MIB
MAC MIB or PIB
MAC MIB or PIB
MAC
MAC
Mgmt Entity
Mgmt Entity
PHY
PHY
Measure Report
Measure Request
Remote Device
Remote metrics carried over network
Coordinator or Access Point

21. Communicating metrics over the HAN
and P1901 provide standardized mechanisms for communicating metrics over the network
defines a type of management frame (action frame) with information elements carrying the metrics
P1901 defines management messages that can be carried over the power line network or Ethernet.
does not define a mechanism to communicate metrics over the air interface.
Possible future work for

22. Application for dynamic fragmentation
g (Smart Utility Network) targets neighborhood area connectivity between Smart Meters
Data rates are 5 – 400 Kb/S
The g Project Authorization Request (PAR) specifies PHY frame sizes up to 1500 octets (i.e. for transport of Ethernet packets).
Packet transmission times up to 2.4 S would result in very low reliability.
Fragmentation at higher layers will be required, but what is the optimum size?
MAC metrics provide a basis for dynamically setting the proper fragmentation size based on conditions.

23. Scenario for system level metrics application
EGW RD
HAN Metrics gathered by Remote Devices (RD)
Metrics monitored over HAN by Energy Gateway (EGW)
EGW contains an SNMP Agent
Represents metrics for all RD’s in HAN
Utility Management and System consolidates and monitors metrics from all HANs - (independent of HAN network technology
EGW RD
Internet
EGW RD
Utility Management
System
HAN (Wi-Fi, HomePlug, Zigbee)
Internet (WAN)

24. Together…Shaping the Future of Electricity