Submission

doc.: IEEE 11-10/xxxxr0doc.: IEEE 11-10/0864doc.: IEEE 11-10/0864

Unified Metrics for Management of Smart Grid Home Area Networks

Date: 2010-07-12

Slide 1 Tim Godfrey, EPRI

July 2010

Name Affiliations Address Phone email Tim Godfrey EPRI

Craig Rodine EPRI

Authors:

2© 2010 Electric Power Research Institute, Inc. All rights reserved.

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© 2010 Electric Power Research Institute, Inc. All rights reserved.

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

4© 2010 Electric Power Research Institute, Inc. All rights reserved.

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 802.15.4)

– Homeplug AV/GP-SE (IEEE P1901)

– Wi-Fi (IEEE 802.11 b/g/n)

5© 2010 Electric Power Research Institute, Inc. All rights reserved.

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.

6© 2010 Electric Power Research Institute, Inc. All rights reserved.

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© 2010 Electric Power Research Institute, Inc. All rights reserved.

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© 2010 Electric Power Research Institute, Inc. All rights reserved.

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

Peer MAC AddressPacket count

Avg LQI

Last LQI Rate Age Beacon

00:0b:6c:5f:6a:ed 1 0x12 0x12 1 38 000:0c:41:e5:37:f8 34 0xf0 0xf6 36 76 000:b0:d0:28:12:d8 11 0xa1 0xa3 6 92 100:30:b4:02:4d:48 148 0x91 0x89 24 583 000:40:96:29:fd:a0 72 0x48 0x44 12 1042 000:19:d2:6b:46:bc 23 0x97 0x9d 24 5483 0

9© 2010 Electric Power Research Institute, Inc. All rights reserved.

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© 2010 Electric Power Research Institute, Inc. All rights reserved.

802.11 (802.11k)dot11TransmittedFragmentCount

dot11MulticastTransmittedFrameCount

dot11FailedCount

dot11ReceivedFragmentCount

dot11MulticastReceivedFrameCount

dot11FCSErrorCount

dot11TransmittedFrameCount

dot11RetryCount

dot11MultipleRetryCount

dot11FrameDuplicateCount

dot11RTSSuccessCount

dot11RTSFailureCount

dot11ACKFailureCount

Derivation of Metrics from 802.11 (Wi-Fi)

11© 2010 Electric Power Research Institute, Inc. All rights reserved.

802.11 (802.11k)dot11TransmittedFragmentCount

dot11MulticastTransmittedFrameCount

dot11FailedCount

dot11ReceivedFragmentCount

dot11MulticastReceivedFrameCount

dot11FCSErrorCount

dot11TransmittedFrameCount

dot11RetryCount

dot11MultipleRetryCount

dot11FrameDuplicateCount

dot11RTSSuccessCount

dot11RTSFailureCount

dot11ACKFailureCount

Derivation of Metrics from 802.11 (Wi-Fi)

12© 2010 Electric Power Research Institute, Inc. All rights reserved.

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)

Derivation of Metrics from P1901 (HomePlug)

13© 2010 Electric Power Research Institute, Inc. All rights reserved.

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)

Derivation of Metrics from P1901 (HomePlug)

14© 2010 Electric Power Research Institute, Inc. All rights reserved.

Metrics for 802.15.4 (Zigbee)

• The existing standard 802.15.4 does not include MAC layer metrics.

• The “philosophy” of 802.15.4 is to keep the MAC very simple and small

– Many applications require low power and low cost

• The complex measurements of 802.11k 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 802.15.4 amendment developed by Task Group 4e

15© 2010 Electric Power Research Institute, Inc. All rights reserved.

802.11 (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

Derivation of Metrics from Existing Standards

• Selected Subset

16© 2010 Electric Power Research Institute, Inc. All rights reserved.

802.11 (dot11Counters Group and dot11MACStatistics Group

802.15.4 (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

Derivation of Metrics from Existing Standards

• Selected Subset - extended to 802.15.4

17© 2010 Electric Power Research Institute, Inc. All rights reserved.

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© 2010 Electric Power Research Institute, Inc. All rights reserved.

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

0

20

40

60

80

100

120

Success 1-Retry Mult-Retry Failure

0

20

40

60

80

100

120

Success 1-Retry Mult-Retry Failure

0

20

40

60

80

100

Success 1-Retry Mult-Retry Failure

Good RF conditions Weak Signal Interference Bursts

19© 2010 Electric Power Research Institute, Inc. All rights reserved.

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 meanssender did not receive the ACK

• Possibly interference local to the sender

octets: 2 2 6 6 6 2 6 2 0-2312 4

Frame Control

Duration / ID

Address 1

Address 2

Address 3

Sequence Control

Address 4

QoS Control

Frame Body

FCS

MAC Header

Figure 12 – MAC frame format 1

X

Transmit Receive

Lost

Frame N

Retry Frame N

ACK

Duplicate

20© 2010 Electric Power Research Institute, Inc. All rights reserved.

Architecture for communicating metrics

MAC MIB or PIB

Mgmt Entity

PHY

MAC

MIB

Mgmt Entity

MAC

PHY

Measure Report

SNMP SET/GET

MAC MIB or PIB

Coordinator or Access Point

Remote Device

Measure Request

MAC metrics

Per-device statistics may be made accessible in

management entitye.g. SNMPMAC

metrics

Remote metrics carried over

network

21© 2010 Electric Power Research Institute, Inc. All rights reserved.

Communicating metrics over the HAN

• 802.11 and P1901 provide standardized mechanisms for communicating metrics over the network

– 802.11 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.

• 802.15.4 does not define a mechanism to communicate metrics over the air interface.

– Possible future work for 802.15.4

22© 2010 Electric Power Research Institute, Inc. All rights reserved.

Application for dynamic fragmentation

• 802.15.4g (Smart Utility Network) targets neighborhood area connectivity between Smart Meters

• Data rates are 5 – 400 Kb/S

• The 802.15.4g 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.

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Scenario for system level metrics application

Utility ManagementSystem

Internet

EGW

RD

RDRD

EGW

RD

RDRD

• 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

RDRD

HAN (Wi-Fi, HomePlug, Zigbee)

Internet (WAN)

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Together…Shaping the Future of Electricity