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Smart Grid research with key findings and conclusions.

Smart Grid research with key findings and conclusions.

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  • Can I have a copy of the thesis.
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  • pls provide the thesis copy . my id is k_gajrani@rediffmail.com

    thanx in advance
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  • @singhprabin
    Sorry for late reply, I don't have rights to share source code! I got it from this person 'Christian Callegari' pls get in touch with him. He has also done similar research

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  • can i get the source code of this research? actually i'm also doing similar one and getting lot of error while simulating.
    prabin_4_u@hotmail.com
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  • dear sir, i would like to have a copy of this thesis, i am currently doing phd research on smart grid. really appreciate if you could assist...cited is must :) thank you. amalina1979@gmail.com.
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  • 1. CHAPTER 1 INTRODUCTION 1.1 Foreground Information The existing power grid of the 20th century needs a complete change owing to poor grid monitoring and control, increasing energy demand, and above all the rising carbon foot prints. Smart grid is an intelligent power grid that monitors electricity usage in real time and reduces stress on the grid. To achieve this, it requires plethora of telecommunication and networking technologies to overcome aforementioned above challenges [1]. Thus, it is a complete transformation of existing power grid into a modern, intelligent, digital, reliable, secure, robust and clean power grid. Smart grid has many facets such as replacing analog with digital devices, legacy point to point with more flexible and intelligent communication between control stations, and replacing existing digital electric and gas meters with smart metering technology. By 2050, power consumption of the US is expected to rise up to 5 TW per year, implying that many more number of transmission lines, transmission substations, and generation plants are required, thereby making a complex tightly coupled network infrastructure with varying levels of stress and loads. With all these hurdles ahead, very little attention has been given in recent years on reliable and efficient power transmission. According to the Energy Independence and Security Act of 2007, National Institute of Standards and Technology (NIST) is assigned a prime responsibility for developing Smart Grid standards, models and protocols. NIST is also being funded by Department of Energy (DoE) for this Smart Grid development process. 1
  • 2. 2 Also, DoE's "Grid2030" is to have a fully automated electric power grid with abundant, affordable, clean, efficient, and reliable electric power anytime and anywhere. DoE in collaboration with North America Electric Reliability Corporation (NERC) and North American electric utilities, vendors, researchers and academia formed North American Synchrophasor Initiative network (NASPInet) framework [2, 3] for monitoring and controlling the state of the grid. NASPInet will comprise of thousands of Phasor Measurement Units (PMU) for measuring current and voltage phase at different locations. NERC has also independently stated Critical Infrastructure Protection (CIP) framework for reliable bulk power transmission [4]. The CIP framework is classified into eight different categories of which CIP-002 discusses requirements of routing protocols for smart grid communications. 1.2 Research Objective The primary focus of this thesis is to present a broad overview of Smart Grid, and then propose a solution to one of the Smart Grid challenges of strictly monitoring the grid. The Smart Grid communication network (bulk power transmission) requires real time grid monitoring and control, to avoid or minimize impact of any future blackout. The Smart Grid's WAN has much more stringent requirements than any other real time applications, such as, for example, the maximum service disruption time of less than 5 milliseconds [2]. In other words, its WAN should be resilient and robust to sustain a link or node failure. Hence, arbitrarily selecting any type of network recovery model is not sufficient for the grid monitoring.
  • 3. 3 Currently, many utility across the grid is using its own proprietary non-routing protocol like Modbus, Fieldbus, and DNP3, over different underlying technologies such as ATM, Frame relay, and SCADA. Clearly, there is a need of interoperability among utilities to gain better understanding of the behavior of the grid. Hence, there is a need of a common routing protocol. To meet the above challenges, it is suggested here to use the MPLS technology for its fast rerouting and packet encapsulation techniques. Furthermore, different network recovery models were compared through extensive simulations by using the ns2 network simulator, upon which the best suitable model for each class of service was proposed.
  • 4. CHAPTER 2 LITERATURE REVIEW To give a broad overview of Smart Grid, this chapter illustrates its drafts, frameworks, standards, and communication and networking technologies that are likely to be used or are currently in use in the Smart Grid network. 2.1 Gap Areas According to the Energy Independence and Security Act (EISA) of 2007, the National Institute of Standards and Technology (NIST) has been assigned the “primary responsibility to coordinate the development of a framework that includes protocols, model and standards for information management to achieve interoperability of Smart Grid devices and systems” [3, 5]. NIST has made a three-phase plan to rapidly set up standards to provide a robust process for continued development and to utilize these standards when needs and opportunities arise. NIST unveiled its first draft in September 2009, for the Smart Grid interoperability standards – “NIST framework and roadmaps for Smart Grid interoperability standards”. The draft discusses a high level conceptual reference model for Smart Grid; it has identified nearly 80 existing standards that need to be made Smart Grid compliant, 14 high priority gaps, and cyber security standards that require new or revised standards. For prioritizing this work, NIST has classified eight priority areas that are critical to existing and in near term for Smart Grid technologies and services. 4
  • 5. 5 1. Wide Area Situational Awareness - This concept has been proposed for decades, but it was never an integral part of the power system. It has been used only for postmortem analysis of the grid till date. However, monitoring the condition of the grid in real or near real time requires a new high speed, reliable and robust communication network, time-synchronized phasor measurement, and capability to transmit data from different legacy/modern smart grid devices across wide geographical areas. Goals of situational awareness are to enable understanding and optimizing management of power grid components and also to anticipate, prevent or respond to power disruption problems. 2. Advanced Metering Infrastructure (AMI) - Successful transformation from existing power grid to smart grid is only achievable through active customer participation. This technology will have smart meters deployed in every household to have two way communications between utility and its customers. The goal of this technology is to reduce stress on the grid and make efficient energy usage. 3. Distributed Grid Management - DGM aims to maximize performance of different power grid components such as feeders, transformers, and other components of networked distribution system, and to integrate them with the transmission system. 4. Demand Response - Giving incentives to residential and business customers to reduce energy usage during peak hours or when power reliability is at risk is the objective behind DR. Utilities, grid operators, and power generating companies will also be benefited from DR because it reduces their financial and operational costs. It is also essential for balancing power supply and demand so that the grid can run efficiently and smoothly. 5. Electric Storage - Storing energy economically has always been a challenge. Energy can be stored directly or indirectly. The significant energy storage technology is hydroelectricity, where water is stored in dams and transformed to energy. New storage capabilities such as pumped hydro stages (PHS) and compressed air energy storage (CAES) would benefit the entire power grid. 6. Cyber Security - Increasing the number of digital devices in the grid and connectivity of one device to another across WANs and LANs has raised the concern of cyber security. Moreover, concern for security increases due to millions of Smart meters communicating to and from the grid. Cyber security ensures the confidentiality, integrity and availability of data for strict grid monitoring and control. 7. Electric Transportation - Reducing green house gas is the primary objective behind Smart grid. Plug-in Electric Vehicle, eCARs, will significantly reduce green house gas, foreign oil dependency, and reliance on renewable energy resources.
  • 6. 6 8. Network Communications - As Smart Grid will comprise of public and private networks, thus it requires many communication and networking standards that need to be tailored according to requirements of different applications, actors, and domains. 2.2 Smart Grid Architecture Surprisingly, today’s power grid was not built on any planned architecture, it is rather the outcome of poor adhoc planning in the past. The reliability of grid was ensured by mainly having excess capacity, with unidirectional electricity flowing from centrally located power plants to end utility customers. The major focus was to meet the increasing energy demands, rather than changing the overall way the system works, and thus there is a need of distributed Smart Grid architecture, with two way power flow across the grid. In the future, the Smart Grid network will comprise of millions of field devices, thousands of substations, and millions of smart meters, and hence there is a need for robust network architecture to manage all these devices. Its architecture will be akin to existing internet which comprises of many networks of networks; similarly, it will consist of many systems of systems and their subsystems architectures. According to the NIST Framework, having a single architecture for Smart Grid is a not practical solution to the problem. Rather, it will have systems and sub-systems architectures. Till date, there is no single architecture for Smart Grid. NIST along with GWAC, NERC, NASPInet, FERC, EPRI, and NEMA is designing Smart Grid architecture. It has adopted reference models that define characteristics, uses, behavior and other elements in Smart Grid domains along with relationship among these domains. The role of all these bodies is to finalize frameworks, roadmaps and reference models for the Smart Grid
  • 7. 7 architecture. The reference model selected should be robust and well documented since a well documented reference models helps in developing new standards and protocols for ensuring interoperability, cyber security, and also defining the architecture of the Smart Grid systems and their subsystems. 2.3 Layers of interoperability NIST describes the conceptual model on the basis of high level categorization approach developed by GWAC [6], and thus, it is worth to mention Grid Wise interoperability framework that has identified eight different Smart Grid interoperability categories. "GWAC stack", an eight layer stack, is focused on technical, informational, and organizational interoperability. The organizational category emphasizes on pragmatic business and policy aspects of interoperation. The informational category emphasizes on semantic aspect of interoperation. The technical category emphasizes on the syntax of the information, and is primarily based on the OSI reference model, and thus this category comprises all the seven layers of OSI. Figure 2.1 depicts the GWAC's eight layer stack that lays the foundation of Smart Grid interoperability requirements. 2.3.1 Technical Drivers The technical drivers consist of basic connectivity, network interoperability, and syntactic interoperability: 1. Basic Connectivity - "Mechanism to Establish Physical and Logical Connections of Systems". The basic connectivity category focuses on digital information exchange between two systems and the establishment of reliable communication path. It comprises the physical and data link layer of the OSI reference model. Common interoperability standards at this level include Ethernet over Fiber, Ethernet over Twisted pair, WiFi, Frame relay, PPP, and EIA-232.
  • 8. 8 2. Network Interoperability - "Exchange Messages between Systems across a Variety of Networks". The network interoperability category focuses on issues arising due to transportation of information between various domains across multiple communication networks. This category includes the network, transportation, and session layer of the OSI model. FTP, TCP, UDP, IPv6, ARP, and IPSec are common interoperability standards. Figure 2.1 GWAC eight layer model provides a context for determining Smart Grid interoperability requirements. 3. Syntactic Interoperability - "Understanding of Data Structure in Messages Exchanged between Systems". Syntactic interoperability refers to mutually agreed syntax and format for information exchange between domains or transacting parties. This represents the presentation and application layer of the OSI model. General standards for interoperability in this category include HTML, XML, SOAP, and SNMP. 2.3.2 Informational and Organizational Drivers Informational Drivers - Informational models are expressed in an object-oriented form in terms of classes or data fields and methods. It is further subdivided into two layers Semantic understanding and business context.
  • 9. 9 1. Semantic Understanding - "Understanding of the Concepts Contained in the Message Data Structures". 2. Business Context - "Relevant Business Knowledge that Applies Semantics with Process Workflow". Standards for informational drivers include IEC 61970 CIM (Common Information Model) power model, object models based on XML, OPC Unified architecture, and IEC 61850 substation automation. Organizational Drivers 1. Business Procedures - "Alignment between Operational Business Processes and Procedures" 2. Business Objectives - "Strategic and Tactical Objectives Shared between Businesses" 3. Economic and Regulatory Policy - "Political and Economic Objectives as Embodied in Policy and Regulation". 2.4 Conceptual Reference Model The conceptual reference model for Smart Grid is divided in seven domains, namely, bulk generation, transmission, distribution, customers, markets, service providers, and operations. Figure 2.2 shows interaction of different Smart Grid domains. These domains are further divided into sub-domains that encompass actors and applications. Actors are devices, systems, or programs that make decisions and exchange information necessary for performing applications. Examples of actors are smart meters, solar panels, IEDs, PMUs, and control systems. Applications, on the contrary, are tasks performed by one or more actors within a domain. The model described here is proposed by NIST, which acts as a tool to identify possible actors and applications in Smart Grid, which will assist in
  • 10. 10 deciding Smart Grid standards and architectures. Figure 2.3 also shows a detailed conceptual model with many communication links between and within networks, such as SCADA, Enterprise Bus, Field Area Network, and Wide Area Network. Many issues , such as security, reliability, QoS, latency and interoperability, need to be addressed in order to fully realize Smart Grid. Since the Smart Grid network will consist of networks of networks with millions of end devices, there is a need to ensure secure information exchange. The following two subsections discuss key outstanding issues of selecting a common communication protocol and the required common communication protocol within and across its domains. Figure 2.2 Smart Grid Domains, sources “NIST interoperability framework” [3]. Note: The blue line in Figure 2.2 represents secure communication flows between seven different domains and the orange (dashed) line represents flow of electricity from bulk generation to end utility customers.
  • 11. 11 NIST Smart Grid Cyber Security Coordination Task Group (CSCTG) is currently identifying the overall threats, vulnerabilities and risks for the seven Smart Grid domains [3]. It is considering layered based approach for smart Grid cyber security, to ensure that even if one layer is compromised, other layers should remain secure; this is referred to as the "a defense-in-depth" strategy. Figure 2.3 Conceptual Reference Diagram of Smart Grid Domains, Sources “NIST interoperability framework” [3].
  • 12. 12 2.4.1 IP Based Networks IP based networks are the most favorable choice for future Smart Grid applications [3]. It is attributed to mature IP standards and widespread acceptance of IP in both public and private networks. Moreover, IP supports bandwidth sharing and increased reliability with dynamic routing capability. There are many Smart Grid applications in the customer domain such as smart meter, thermostat, electric storage, and appliances. Phasor Measurement Units (PMU), electronic storage, and field devices in a transmission distribution network require varying classes of services like QoS, minimum latency maximum packet loss, or minimum bandwidth constraint. All these requirements can be achieved through IP based communication networks. 2.4.2 Smart Grid Technologies There are a number of mature Smart Grid technologies, which may be used in different Smart Grid domains and their sub-domains. NIST has proposed a partial list of technologies for Wired and Wireless networks [3]. Wired Network - WDM, SONET/SDH, Fiber paths, PON, Gigabit Ethernet, PLC Wireless Network - IEEE 802.11, 802.15, 802.16, 3/4G. Many other independent bodies have proposed different communication technologies for Smart Grid including Internet2 and Ethernet over Fiber for Backhaul network, Broadband over Power Line (BPL), WiMax for Mid-haul, 3G Wireless data and voice, and Zigbee/WiFi for the lastmile networks [7].
  • 13. 13 2.5 Advance Metering Infrastructure The utilities industry has been investing in Automated Meter Reading (AMR) for over more than two decades. Utilities can consistently collect meter data and keep them in a central database to analyze and monitor electric usage by using the AMR technology. The main advantage of this technique is to lower monthly trips required to check meter reading. Moreover, it helps utilities and power generating companies to efficiently manage energy. Efficient grid monitoring requires two way information flow, and hence Advance Metering Infrastructure (AMI) has emerged. AMI is a combination of technologies for measuring, storing and analyzing data collected from gas and electric meters in real-time. It basically consists of the following three parts: smart meters, communication network, and meter Data Management Application (MDMA) [8]. The prime objective of this technology is to reduce stress and operating cost of the grid by setting real time or near real time meter pricing. Traditional electromechanical meters have their readings read once per month, but AMI allows monitoring of hourly or daily energy usage pattern of consumers. Energy consumed per hour or in every fifteen minutes is recorded by smart meter, and is sent over communication networks to utilities companies for monitoring and control purposes. These networks also send real time pricing and control signals to smart meters for efficient energy usage. MDMA is a computer hardware and software application at a utility center that analyzes energy consumption and set dynamic meter pricing. It is worth mentioning that dynamic price control does not control devices like thermostat, gas, water or electric meter at customer premises. Controlling of these devices according to dynamic pricing can be achieved through a sensor network.
  • 14. 14 Many utilities around the world are deploying millions of smart meters at consumer’s premises and business buildings for reducing stress on the grid, and, moreover, encouraging customers to monitor the usage on an hour or day-to-day basis. One of the critical challenges facing these utilities is to ensure that the selected technologies for AMI are interoperable and comply yet-to-be-established national standards [3]. Furthermore, many utilities want to ensure that technologies they have selected, should allow for evolution and growth as Smart Grid standards evolve. It is required to keep motivating utilities, for deploying Smart meters without concerning the future risk of firmware upgrade as Smart Grid is upgraded. NIST has identified this need of AMI as one of the eight priority areas requiring immediate attention. Thus, NIST requested National Electrical Manufactures Association (NEMA) to develop national standards for Smart metering technology. The standard is referred to as NEMA SG-AMI 1-2009 - "Requirements for Smart Grid upgradeability". The objective behind this standard is to define requirements for smart meter firmware upgradeability for stakeholders, regulator, vendors, and utility customers [9]. One of the problems faced by utilities is the use of proprietary communication protocols by different suppliers, and thus utilities are compelled by suppliers to use same proprietary protocols to communicate with end customers. Thus, ANSI proposed standards for interoperability and supporting multiple electric meter manufacturers. The first standard in the field of electric metering was the ANSI C12.18-1996, which is a point-to-point protocol for transporting table data specified by ANSI C12.19 via infra-red optical port. The ANSI C12.19-1997 - "Utility Industry End Device Data Tables" defines a set of flexible data structures for use in metering products. It is just a template for
  • 15. 15 transporting data without mentioning of how to store data. The end device only needs to create data in the proper form and order when information is requested, and to accept information in the proper form and order when it arrives. Furthermore, the ANSI C12.21-1998 standard was specified for communication over modem lines between end customers and utilities. All the above three standards facilitate the transmission of meter data over optical ports or modem lines. These standards are widely accepted in commercial and industrial meters, but using the above standards hinders the holistic view of grid monitoring owing to point to point communication protocols. Finally, a new standard, ANSIC12.22, is specified to overcome the aforementioned challenge. The main objective of this new standard is to create a common communication platform. It is an open standard that enables transportation of C12.19 table over any underlying network and supports interoperability among communication modules and meters [10]. The protocol does not specify how to transport C12.19 over the OSI reference model. There are primarily two different types of models proposed in the standard for transportation of metering data. Firstly, meter with an integrated network connection only specifies the OSI's application layer protocol, and has the flexibility to implement any lower layer protocols. Secondly, Meter with a separate Communication Model (CM) --- the interface between CM and meter --- is explicitly defined from the application layer down to the physical layer. Unlike C12.18 and C12.21, CM supports both session and sessionless communications. In session communication, both ends record and keep track of information requested and granted. In sessionless communications, neither ends records or tracks any information, and thus it is less
  • 16. 16 complex to implement. Figure 2.4 illustrates session and sessionless communication information exchange of C12.21 and C12.22 standards. C12.22 provides an improved security as compared to C12.18 and C12.21 because these two protocols use unencrypted form of information exchange. C12.22 uses the AES encryption technique [11, 12] to enable strong, secure Smart Grid communications, since information from meters will be sent across internet which is an open channel for intruders to sniff the information. In practice, C12.19 does not require any encryption technique because it uses point-to-point communication protocol over optical port; also, C12.21 transmits over telephone modem lines, and thus it becomes very hard for intruders to eavesdrop the information. Computer Meter Computer Meter I den tify R e ad AC K o nse a ut he wi th e sp n ti ca t Id en t if y R io nd A CK d Re a Ne go t ia t A C K an se n e R e spo A C K sp on se e Re Ne g ot ia t A CK Lo go n C 12.22 A C Kpo nse es Lo go n R A CK S ec u ri ty A C K p o nse R es Se c urity A CK Re ad A C K on se sp R e ad R e A CK Te rm in a te A C K spo nse e Re Te rmi nat A CK C 12.21 Figure 2.4 Information exchange in C12.21 and 22 standards [12].
  • 17. 17 C12.22 also supports reliable data transfer over TCP, which is required to transmit packet in a network where high error and retransmission rate exists. Reliability was not the concern in prior metering standards, C12.18 and C12.21, since it is very hard to eavesdrop any bit of information in point-to-point communications. As stated earlier, C12.22 supports sessionless communications, and thus it supports faster meter data transmission. It means that a single transaction can support authentication as well as read billing data request without the usual overhead of a table read transaction. Currently, ANSI C12.22 is in a draft stage for “C12.22 data transport data over IP” [11]. Many communication technologies including Zigbee, Z wave, Wi-Fi, BPL, Internet, Wimax, Mobile Network, and RF can be adopted for advance metering infrastructure (or for last mile and Midhaul networks).. With AMI technology, consumers are encouraged to use electric appliances during off peak hours, since during that time period, meter pricing will be least. For example, the cost of electricity during off peak hours, i.e., 10:00 PM - 06:00 AM will be lower than during peak hours, i.e., 7.00 AM to 9:00 AM. This energy consumption pattern will ease stress on the grid. States of California, Texas, and Minnesota will be the forerunner in AMI since they are in the pilot phase of deploying and testing millions of smart meters. AMI faces many challenges like opting best communication technology that will last at least twenty to thirty years and security breach by some malicious customers.
  • 18. 18 2.6 Transmission and Distribution Network The electric transmission network is one of the oldest and complex network infrastructures. There are more than 150,000 miles of transmission lines running all across the US [13], with the majority of using AC transmission lines. This is because the power lost in AC, during long distance transmission is less in comparison to DC. Broadly, the electric grid in the US is divided into three independent interconnects: Eastern, Western, and Texas interconnect. All the three interconnects are connected to each other through high voltage DC lines, in case power needs to be rerouted across interconnects. With 186 major transmission paths in the eastern interconnect, 50 are used to its maximum capacity at some point of time in the year [13], and thus requiring robust communication network to monitor the state of the grid. Eastern interconnect is and will always remain under more stress in comparison to the other two since half of the US population lives on the east coast. That was also why the August 2003 blackout occurred in the eastern interconnect. The actual reason of this massive blackout was caused by the Eastlake power plant which was incapable of meeting high electric demand, thus putting stress on the transmission line. This problem got worse when FirstEnergy failed to trim stress on time, which eventually led to power sagging. Generally, all power generation plants are interconnected to each other through the electric grid. So, if there is a power outage in some locality or some generation plant is incapable of meeting energy demands of particular locality, then power is rerouted to these localities from some other generation plant that can meet energy demands. However, owing to the poor communication network, this information could not be passed to other plants, and thus
  • 19. 19 leading to the cascading effect. According to some researchers [14, 15, 16], the blackout could have confined to a smaller region if we had a robust wide area monitoring and control system. Existing transmission network is typically operated by Regional Transmission Operator (RTO)/ Independent System Operator (ISO) whose primary responsibility is to balance generation with load across the transmission network. Presently, this transmission network is monitored and controlled through the SCADA system composed Figure 2.5 Complex power transmission network with 137 BA with AC and DC transmission lines [17]. of different communication devices [18]. The SCADA system will be discussed in more details in later part of this chapter. It is worth to mention that SCADA systems are out of place for grid monitoring due to their average RTU polling time of 4 seconds [19]; this is
  • 20. 20 unacceptable for the Smart Grid monitoring where service disruption is confined to be in the order of few milliseconds. 2.6.1 NASPInet Framework The Department of Energy (DoE) along with North American electric power industries, utilities and North American Electric Reliability Coordinator (NERC) formed the NASPInet framework (formerly known as Eastern Interconnect Phasor Project EIPP) for wide area monitoring and controlling the grid. The objectives of this framework are to decentralize and standardize existing synchrophasor measurement system. Synchrophasors are precise measurements of the grid from Phasor Measurement Units (PMU). At present, there are 56 PMUs in the western interconnect and 105 in eastern interconnect. However, by the year 2019 [20, 21], there will be thousands of PMU in each interconnect. 1. Phasor Measurement Unit (PMU) – It is a device which calculates current and voltage (both phase and magnitude) of different components in a power system like transmission path status, generator load, active and reactive power, etc. If the calculated value differs from the reference value, a trigger is generated notifying instability in part or sub-part of the grid which technically means that the electric load differs with the mechanical power. Typically, PMU samples at the rate of 30 frames/second (fps) - in comparison to 4 seconds polling time in conventional techniques, for strict grid monitoring. In the future, depending on the required level of accuracy, it will sample current and voltage at varying data rate of 10, 20, 30, 60 or 120 fps. 2. Phasor Data Concentrator (PDC) - It collects phasor data from PMUs, other PDCs, event data, and stores and forwards data to PGWs located in control centers. PDCs time aligns sampled data from different utility with GPS technology, thus providing a precise and broad view of the region having multiple transmission stations and substations. Data generated from all PDCs should have Universal Time Coordinated (UTC) of less than 1µsec. Archived data is helpful during grid instability for analyzing the problem.
  • 21. 21 Figure 2.6 Proposed NASPInet WAN 3. Phasor GateWay (PGW) - Each Balancing Authority Area (BAA) or control center will have single PGW, which will forward traffic received from PDC to another PGW. Functions of PGW are monitoring real time traffic, latency, dropped packets, and detecting corrupted packet [22]. NASPInet will have private WAN of PGWs with the life span of at least 30 years with minor maintenance in hardware and software. Currently, there are 150 Balancing Areas in the US, thus comprising WAN of 150 PGWs [45]. It is a complex network of interconnected PGWs that needs to be controlled and monitored very precisely. 2.6.1.1 NASPInet WAN It will be a private network of Local Area Networks (LAN) and Wide Area Networks interconnecting thousands of PMUs by the year 2019, the year when phasor measurement technique will be fully deployed and functional. It is open network architecture to allow addition of future functionality, industrial standard of hardware, software, and replacement without interrupting its normal operation. Requirements of this WAN are
  • 22. 22 1. Path of Redundancy - NASPInet WAN network will have redundant path to overcome any single link failure. The network design will ensure the data delivery time, maximum interrupt time, and system recovery time. Since class A and B data will require high availability of path and least interruption times, the NASPInet WAN shall implement independent redundant path for these classes. These independent redundant paths will not share any devices or components along their path, be it be virtual channel or physical components. 2. QoS - NASPInet will maintain full end to end Quality of Service for all the five classes of services between ingress and egress PGW. The QoS here is defined in terms of least delivery time, least service disruption time. 3. Traffic Prioritization - The NASPInet WAN shall have traffic prioritization for each class of service. That is, Class A traffic will have highest prioritization and Class E the lowest prioritization. 4. Disaster Recovery - The network should support major disaster recovery. Particularly, class A and B data flow should not be interrupted, and interruption of other data class is permissible within maximum disruption time. 5. Network Protocol - The future WAN should fully support IPv6; if not all components, at least core components of the backbone should support Ipv6. For the pilot or initial implementation, IPv4 can be used. Although recommended network for WAN is private, but if the utilities use public network, then the network should support guaranteed bandwidth. Network should support industry standard protocol, that is reliable, scalable, providing alternate routes, and resilient to fault tolerance. NASPInet classifies different kinds of information generated from PMU like control feedback, feed-forward, display, etc., into five different classes of services. Table 2.2 shows the maximum disruption time and acceptable end to end latencies for these classes. End-to-end latency is calculated as the time difference when a packet reaches ingress PGW to the time when it exits from an egress PGW. Also Table 2.3 shows traffic priority according to different class of service, highest priority is for class A and lowest is for class D and E data.
  • 23. 23 1. Class A: It will be assigned to applications requiring least service disruption and minimum end-to-end latency, such as real time streaming for feedback control. 2. Class B: Applications which can sustain higher disruption and end to end latency than “class A” service will be categorized into this service class, like feed-forward control and state estimator. 3. Class C: Applications with higher tolerance of disruption time will be categorized into this class, like visualization to system operator. 4. Class D and E: former service class will be used for off-line and post- mortem analysis in case of component failure, and later one for scientific and research purpose. Table 2.1 Service Disruption and Latency Time for Different Class of Service Class of Data rate Availabilit Service End to Description Service (fps) y (%) Disruptio End n Time Latency Feedback A 30, 60, 120 99.9999 <5 msec <50 msec Control Feed forward B 20, 30, 60 99.999 <25 msec <100 msec control Display C 10, 15, 20 or 99.99 <100 < 1 sec 30 msec Disturbance D 30, 60, or 99.99 N/A <2 sec analysis 120 Research E 30, 60, 120 99.99 N/A <2 sec 2.6.1.2 IEEE C37.118. IEEE C37.118 – Prior standard for synchrophasor real time Wide Area Monitoring System (WAMS) was IEEE 1344, which was reaffirmed in 2001. In 2005, it was changed to IEEE PC37.118.2005 due to some drawbacks which emerged during August 2003 blackout. Key features added to this protocol were improved information exchange with non phasor systems, sync frame, frame size, station identification number, configuration, header frame, and command frame [23]. PMUs
  • 24. 24 from different vendors may have discrepancy in monitoring and controlling power system, and so variation in measurement concept of TVE (Total Vector Error) was added to overcome this drawback. Table 2.2 Traffic Priority for Varying Class of Service Note: “4” represents highest priority and “1” least priority. NASPInet Class A Class B Class C Class D Class E Traffic Low latency 4 3 1 2 1 Availability 4 2 3 1 1 Accuracy 4 2 4 1 1-4 Time 4 4 1 2 1-4 alignment High 4 2 4 2 1 message rate Path 4 4 1 2 1 redundancy This protocol is defined for real time data transmission to and from PMU [23]. The protocol is only required if the PMU device is to be used with other power systems such as digital fault recorder (DFR), Dynamic System Monitor (DSM), and Digital Signal Analyzers (DSA) interface to macro dyne. If PMU needs to only archive data for future purpose such as analyzing grid instability, then this protocol is not needed. There are four types of message formats and five types of commands used for communication between PMU and PDC of which Data frame is most often used. 1. Data Frame – It consists of sampled real time measured phasor data such as magnitude, phasor, and frequency, sent from PMU to PDC. Size of data frame is variable, due to varying level of precisions required. That is, high precision application requires more frames than the usual 30fps to be monitored at 60 or 120 fps. Size of one frame is 128 byte. Figure 2.5 shows the frame transmission order.
  • 25. 25 2. Configuration Frame – It contains information and processing parameters for the PMU. There are two types of configuration frames, config-1, and config-2. Config -1 represents constant configuration information of PMU and config-2 represents variable configuration information of PMU, like variable data rate. 3. Header Frame – It contains descriptive information that is sent from PMU to PDC. 4. Command Frame – There are five command frames that are sent from PDC to PMU to start or stop measuring phasor data. TRANSMITTED SYNC FRAMESIZE IDCODE SOC FRAMESEC FIRST 2 2 2 4 4 CHK TRANSMITTED DATA 1 DATA 2 DATA N LAST 2 Figure 2.7 PMU Frame transmission order, source [23]. Phasor data generated from PMU is sent to PDC, where it is transported over UDP/IP that provides connectionless, reliable and faster service for time sensitive applications. The standard does not define any particular communication medium between PMU and PDC. Generally, utilities use dial-up or serial communication link for transporting phasor messages. Phasor data generated from PMU is sent to PDC, where it is transported over UDP/IP that provides connectionless, reliable and faster service for time sensitive applications. The standard does not define any particular communication medium between PMU and PDC. Generally, utilities use dial-up or serial communication link for transporting phasor messages. Table 2.3 Illustration of PMU-PDC Frames and Commands
  • 26. 26 Frame PMU PDC Message Format Functions Data → Binary Real time phasor information – magnitude, phase, angle Config- 1 → Binary Constant parts of PMU (Machine reliable) configuration Config - 2 → Binary Variable part of PMU (Machine reliable) configuration, no. of phasors Header → ASCII Any other information (Human reliable) Command → Binary Start, stop, config-1, (Machine reliable) config-2, header command to and from PDC 2.6.2 NERC CIP Framework The objective of this framework is make reliable and secure bulk power transmission. North American Reliability Corporation (NERC) has outlined cyber security requirements for the Critical Infrastructure Protection (CIP). It provides a cyber security framework for the identification and protection of Critical Cyber Assest (CCA) to support reliable Bulk power transmission. CAAs include power plants, control center, backup control center, and transmission substation that provide bulk power generation, monitoring and control of real time inter utility data exchange. There are eight different cyber security standards defined from CIP 002 to CIP 009 that deal with critical cyber asset identification, security management control, personnel training, electronic security parameter(s), physical security, system security management, incident reporting and resource planning, and recovery plans [4]. CIP 002 is the most important standard with respect to this thesis since it deals with routing and outlines characteristics in terms of
  • 27. 27 communications and cyber assets, According to the CIP 002 standard, a CAA asset should have at least one of the following three characteristics [24]. 1. The Cyber Asset uses a routing protocol to communicate outside the Electronic Security Perimeter. 2. The Cyber Asset uses a routable protocol to communicate within a control center. 3. The Cyber Asset is dial-up accessible. Dial-up accessible refers to any temporary, interruptible, or not continuously connected communication access to critical cyber asset from any remote location. For example, utilities use modem over land line, wireless, or VPN with routable protocol to connect a critical cyber asset from one or more locations. Any access to a critical cyber asset via a permanent communication link or dedicated communication circuit would not be considered as dial-up access. 2.7 Power Plant Communications Supervisory Control and Data Acquisition – SCADA collects data from sensors, actuators, Intelligent Electronic Devices (IED), and switch relay in a substation, and reports to Master Controller, which thus co-ordinates and controls among different field devices. Here, SCADA is discussed in terms of power plant communication, but it is also used in substation communications as well. Field devices are controlled near real time vai the SCADA system. Basic components of SCADA include RTU (Remote Terminal Unit) and MTU (Master Terminal Unit), in which RTUs collect data from sensors, Intelligent Electronic Devices (IED) and other field devices, and report to MTU or HMI (Human Machine Interface). Communications between RTU and MTU uses contention method
  • 28. 28 CSMA/CD to avoid collision of frames. MTU/HMI monitors and controls various field devices. The SCADA communication network in the past had been lease lines with point to point and multi-drop configuration in lines. However, present communication networks are using fiber optics, frame relay, ATM, Ethernet, T-1 lease line for RTU- MTU communications. One of the major drawbacks of the SCADA system is that the MTU polls many RTUs over a single link and the average polling time of any RTU is nearly 4 seconds. This delay of 4 seconds is unacceptable if power grid has to have 99.9999% reliability, i.e., power disruption of less than ½ second/year. Distributed Network Protocol 3.3 (DNP 3.0) and IEC-60870-5 are the two open communication protocols used in the SCADA system. The later one is used in Europe, and the earlier one is used by rest of the world. DNP3.0 is an open standard, communication protocol used to communicate between RTUs, MTUs, and various other field devices like Digital Relay and DFR. It is also used for inter utility communications. DNP3.0 is based on the 3 Layer Enhanced Performance Architecture (EPA) model which was created by the International Electrotechnical Commission (IEC). Existing communication protocol for communicating between various SCADA systems across WAN is Inter Control Center Protocol (ICCP) or IEC 60870-6. This protocol is based on the client server model. For example, control center A may be a client which requests for real time data from another control center B. A control center can be a client or server. In general, a client is usually connected to many servers, and a single server is connected to many clients. Figure 2.8 shows the existing WAMS network with limited number of PMUs and IEDs that still uses ICCP for monitoring the grid.
  • 29. 29 Figure 2.8 Existing WAMS, using ICCP for grid monitoring.
  • 30. CHAPTER 3 TECHNOLOGY FOR THE GRID MONITORING Previous chapters discussed broadly about various aspects of Smart Grid. This chapter discusses about choosing a technology for Smart Grid monitoring, keeping in view new and legacy technologies currently installed in different power plants and substations. 3.1 Challenges for Utilities According to FAQs of NERC CIP-002 standards, routing protocols are those that provide layer 3 (routing) and above routing functionalities of the OSI reference model [4]. However, most of the present utilities are still using non-routing protocols such as DNP3.0, Profibus, Modbus, and Fieldbus, implying that they do not have routing functionalities. These protocols have interface directly from application layer to data link layer. This means that for these protocols to have routing functionalities, they must be run over IP, like DNP over IP, Modbus over IP. Within utilities, there are several kinds of networks deployed such as SCADA, AMI, ATM, Frame relay, and PSTN in which each of these networks is maintained separately. With the growing number of smart grid applications, the size of these network increases, and it becomes very difficult to manage these networks individually. Thus, there is a need for a consolidated network that can comprise all legacy technologies. One of the major challenges ahead for utilities is to provision reliable inter-utility real time communications, so as to avoid any future blackouts as stated earlier, which will incur catastrophic losses. The communication protocol selected for Smart Grid should be 30
  • 31. 31 robust to accommodate all existing and new kinds of applications [13]. According to some researchers [15], the August Black Out could have been avoided if we would have been equipped with highly efficient and reliable communication network between utilities. 3.2 Why not ICCP for Grid Monitoring? Inter Control Center Protocol (ICCP) or IEC 60870-6 is a real time data exchange protocol for exchanging data between utilities and RTO/ISO across WAN. ICCP works at layer 7 of the OSI reference model [25], and so it utilizes application layer services to establish and maintain logical association between control centers. Since ICCP is independent of lower layers, it can also be operated over TCP/IP. Although ICCP is capable of being able to run over TCP/IP, it is not suitable for carrying real time synchrophasor data communication; ICCP is not suitable for scenarios with high sampling rate of phasor data [26] since it does not generates time stamp required to accurately monitoring and analyzing the grid condition. Time stamped data is also required for futuristic grid performance, which the existing ICCP protocol does not provision. Figure 3.1 shows the existing layout of wide area monitoring by the ICCP protocol with different utilities connecting each other through different technologies and protocols
  • 32. 32 UTILITY – D MODBUS over IP UTILITY – A FRAME RELAY over IP ICCP UTILITY – B SCADA over IP UTILITY – C ATM over IP Figure 3.1 Existing ICCP protocol for – C exchange between utilities. UTILITY data DNP3.0 over IP 3.3 Why MPLS? Before discussing the benefits of the MPLS technology, it is worth comparing the requirements of the smart grid communication network and existing core internet backbone network. This comparison is necessary since it decides by what degree smart grid network will differ from the existing core network. Table 3.1 summarizes requirements of the smart grid network in comparison features exhibited in the present core network. Smart has two major challenges of grid monitoring and control, and grid security, further to meet these challenges there are two frameworks NASPInet and CIP, which has requirements of end to end latency for different classes of services and selected protocol must have routing and switching functionality as described in OSI reference model respectively. Thus MPLS meets all the above challenges due to packet encapsulation, network recovery, and VPN feature, and adheres to the requirements of both the frameworks. Figure 3.2 shows the block diagram for choosing the MPLS technology for the smart grid communications.
  • 33. 33 Securing the grid according to NERC CIP standards is essential for utilities. Utilities have to bind to CIP standards for securing the power grid. So, utilities have three of the following options to adhere to CIP standards [4]. Table 3.1 Comparison between Core Backbone Network and Smart Grid WAN Network Existing Smart grid Requirements core network wide area network QoS requirement Yes Yes Scalability Yes Yes End to end latency requirement Yes Yes High complexity Yes No (for the near future) Support of real time traffic Yes Yes Redundancy, Yes Yes quick traffic reroute Security Yes Yes Load balancing Yes No (for the near future) Routable protocol Yes Yes Not at present, High bandwidth Yes but surely in future. Complex mesh topology Yes Not, at present 1. Removing all routable communications to substations. 2. Reverting back to serial communication over frame relay circuits or narrow band point to multipoint SCADA (layer 2 only). 3. Enabling IP communications (layer 3) and becoming compliant with NERC CIP standards. Avoiding routable communication between substations is not a favorable solution, hence utilities are implementing layer 2 and layer 3 solutions to enable NERC CIP standards. Thus, the best suitable option for utilities is to have Multi Packet Label Switching (MPLS) for having layer 2 and layer 3 functionalities as required by CIP 002.
  • 34. 34 SMART GRID Grid monitoring Grid Security and control Any framework ? DoE’s NERC’s NASPInet CIP 002 Requirements ? Protocol should have End to End Latency for switching and routing different class of service functionality as described in OSI Protocol for WAN ? Packet encapsulation (ATM, Frame MPLS relay), Security, VPN, Network Recovery Figure 3.2 Technology for the grid monitoring: suggested technology adheres to NASPInet and NERC CIP requirements. 3.4 Benefits of MPLS
  • 35. 35 MPLS provides many benefits over existing similar technologies like traffic segmentation with VPN, Traffic Engineering (TE), QoS, network resilience, consolidation, and security. Many power generating companies use legacy technologies such as ATM, Frame Relay, Ethernet, and TDM for communication between different power generating companies [28], and hence MPLS is the appropriate technology owing to its backward compatibility by virtue of its multiprotocol encapsulation technique. It provides security through traffic segmentation; basically there are three types of MPLS VPNs deployed in today’s networks, namely, point to point, layer 2 VPN, and layer 3 VPN for routing different kind of traffic over the MPLS backbone. Point-to-point MPLS VPNs employ Virtual Leased Lines (VLL) that is used to provide layer 2 point-to-point connectivity between two sites for carrying Ethernet, TDM, and ATM frames [29]. Layer 2 VPN or Figure 3.3 Suggested NASPInet WAN, with MPLS technology for grid monitoring. Virtual Private LAN Service (VPLS) provides ability to span VLANs between sites. It is used to route voice, video and ATM traffic between substation and datacenters. Layer 3
  • 36. 36 VPN or IP enabled VPN is becoming choice for utilities since it enables them to communicate irrespective of layer 2 technology, for example utility A may connect with Ethernet to utility B and C using frame relay or SCADA. High speed, real time synchrophasor data transmission and analysis are required to gain deep visibility into the power grid. With such a requirement, it is necessary to have robust and resilient network for carrying synchrophasor data. MPLS provides various network recovery models like fast reroute and dynamic rerouting depending upon the requirements of particular class of service. Figure 3.3 shows suggested WAN enabled with MPLS technology that will provide network resiliency, robustness and security.
  • 37. CHAPTER 4 NETWORK RECOVERY WITH MPLS 4.1 Background Existing routing protocols used in present Internet backbone are OSPF, IS-IS, and BGP. Although these protocols are robust and survivable, but the amount of time they take to recover in case of a network failure is in the order of seconds or few minutes. This much amount of disruption time is unacceptable for critical network applications. Multiprotocol Label Switching provides proactive/reactive alternate paths (backup path or protection path) to quickly reroute the traffic. MPLS is a mature technology which has been readily deployed successfully owing to its faster traffic rerouting capability, in case of a link or node failure. As wide area monitoring of grid will likely make use of the optical backbone for carrying data between multiple PGWs, it is equally likely for this kind of critical network to have a node or link failure owing to fiber cut or component failure. Since the links will be carrying high priority data with some class of service permissible to a maximum disruption time of only 5 milliseconds. Hence, Smart Grid WAN should provision network recovery to avoid service disruption. There has been different network recovery schemes proposed for SONET, IP, Optical Protection, and MPLS. According to Reference [30], the MPLS based recovery scheme outperforms as compared to other technologies for the following reasons with respect to smart grid requirements. 37
  • 38. 38 1. IP rerouting is too slow for a core network since it has recovery time smaller than convergence time 2. IP rerouting cannot provide bandwidth protection required by certain classes of services in smart grid. For example, when PMUs will be generating data at 60, 120 or 250 samples/sec in the future, high bandwidth is required for link protection. 3. Recovery mechanisms in the optical layer or SONET do not consume resources efficiently. 4. Recovery mechanisms in the optical layer or SONET do not differentiate traffics into different classes of services. That is, if these technologies are used in smart grid, then class A and class E data will be treated equally, and the same fast restoration scheme will be employed. Thus, resources allocated to class E will lead to inefficient resource utilization. MPLS establishes interoperability of protection mechanisms between PGWs from different vendors in IP or MPLS network that is a required property to enable network recovery between PGWs from different vendors. 4.2 Definitions Recovery Path or Backup Path - It is the path by which traffic is restored after a link or node failure. The recovery path can either be an equivalent recovery path with the same QoS and bandwidth guarantee, or with limited recovery path with compromised QoS. Label Switch Router (LSR) - It is the core MPLS component used for forwarding traffic on the basis of labels attached to it. Path Switch LSR (PSL) - It is a label switch router responsible for rerouting traffic in case of a link/node failure. Path Merge LSR (PML) - Path Merge LSR – It is a LSR at which traffic flowing through the backup path is merged back to the working path.
  • 39. 39 Bypass Tunnel - A path that serves to backup a set of working paths. The working paths must share the same PSL and PML. Switch Back - The process of switching traffic back from one or more recovery paths to the original working path. Switch Over - The process of switching traffic from a working path to one or more alternate paths. 4.3 Network Recovery Schemes There are two types of network recovery schemes, namely, protection and rerouting. Protection switching reroutes traffic according to pre-computed paths, and rerouting switching finds a new optimal path upon a network failure. Protection switching This recovery scheme pre-computes an end to end recovery path or a segment of path according to network policies, traffic, bandwidth, delay requirement for different classes of traffic. When the failure, either link or node failure, is detected in the network, traffic is rerouted to the recovery path and the service is restored. The alternate path may be used to either carry copy of the original traffic or reroute traffic upon fault detection. Protection switching is thus divided into two sub-protection switching schemes. 1. 1+1 (one plus one) – Network carries the same traffic on alternate back up path as it carries on the working path. The major advantage of this switching protection is that there is no data loss, and service is not disrupted since traffic flows in both paths. The disadvantage of this scheme is low efficiency as resources have to be allocated throughout the traffic flow. 2. 1:1 (one to one) – the protected traffic flows on the working path, and it is switched to alternate backup path in case of a link/node failure. The advantage of this scheme as compared to 1+1 is that less resources need to be allocated. The disadvantage of this scheme is that once the traffic is rerouted to the
  • 40. 40 backup path, the low priority traffic flowing in the backup path is dropped or replaced by this high priority traffic flow. There are few variants to this scheme like 1:n (one to n) and m:n (m to n). In 1:n, “n” working paths are protected by only one backup path, and in m:n, “n” working paths are protected by “m” backup paths. Rerouting This recovery scheme, as the name implies, selects a new optimal path upon detection of a network failure. The new path is selected based on network policies, like bandwidth guarantee and network topology. The service restoration time in this kind of recovery model is typically longer since after failure detection, routing table needs to be updated, and converged; the scheme has to select the best available backup path according to the new routing table. Recovery Cycles There are three defined recovery cycles; MPLS Recovery cycle model, MPLS based Reversion Cycle Model, and Dynamic rerouting cycle model. The MPLS recovery cycle model detects a fault and reroutes traffic onto the MPLS paths. If the path on which traffic is rerouted is not optimal, it uses the other two recovery models. It uses MPLS Reversion cycle model for explicit path rerouting, and uses dynamic reroute traffic for forwarding traffic on hop by hop routing. 4.3.1 Local Repair Local repair is also known as distributed repair. The key idea behind local repair is to protect a single link or node failure. In local repair, the node that detects failures initiates the traffic rerouting process. This kind of scheme has the advantage of faster recovery time and lower packet dropping, but one of the drawbacks with this kind of topology is
  • 41. 41 that it consumes and requires a greater amount of network resources. There are two types of local repair topology. 1. Link Recovery/Restoration – The recovery path is configured around an unreliable link. The alternate backup path selected should be disjoined from the working path. The traffic on alternate path is routed by upstream LSR. 2. Node Recovery/Restoration – The recovery path is configured around a node that is unreliable. Also, in this model, selected backup path should be disjoined from the working path. 4.3.2 Global Repair It is also known as end to end or centralized repair. The key idea behind global repair is to protect against any link/node failure on the entire path. In global repair, the node that sends Fault Identification Signal (FIS) may be distant or near to ingress LSR depending on how far link/node failure occurred from ingress LSR. The global recovery path is completely link and node disjoint from the working path, and thus global repair has the advantage of better resource utilization. The major disadvantage of this topology model is that it has longer service disruption time than that of the local repair model since the time taken by the FIS signal back to PSL depends on the distance between failed link/node and PSL itself.
  • 42. 42 4.4 Label Distributions There are different kinds of signaling protocols used for exchanging labels between adja- cent LSRs. These labels are exchanged to set up Label Switch Path (LSP) for establish- ing VPN link or rerouting traffic explicitly between LSR. Below are four different kinds of commonly used LDPs. 1. Label Distribution Protocol (LDP) – It is a protocol for exchanging label for FEC mapping between LSRs to establish LSP. The two LSRs must adhere to a common set of procedures for establishing paths. Two adjacent LSRs running LDP are known as LDP peers. Each LDP peer may have multiple interfaces through which they are connected so that they may maintain different LDP ses- sions using different interfaces. An LDP session is bidirectional in nature so that path can be established by any of the peers. LDP works closely with IGP in se- lecting a route to destination on hop by hop basis, and thus it does not support Traffic Engineering (TE) [31]. There are two types of label space defined, name- ly, per-interface and per-platform label space. Per interface label space is com- monly used by LER that has ATM or frame relay interface, and Per-platform label space is used by non-ATM/frame relay interface. 2. Constrained based Routing LDP (CR-LDP) – In LDP, the path selected to the destination is the shortest path since it is based on the Bellman Ford’s algorithm, but it might not be the best path. To overcome this drawback, CR-LDP was pro- posed that uses distance vector to find the shortest path with traffic engineering. Though the path selected to the destination might be shortest but it could be con- gested, and so other links which may be available in the network are underuti- lized. To achieve this goal, the concept of explicit route (ER) was introduced and incorporated into LDP. When ingress LSR wants to establish a tunnel to egress LSR, CR-LDP runs the Constrained Shortest Path First (CSPF) algorithm, and then creates the label request message and inserts an explicit route object in the la- bel. Egress LSR upon receiving a label request replies with a label mapping mes- sage. 3. Resource ReSerVation Protocol with Traffic Engineering (RSVP-TE) – The signaling protocol was proposed for applications which require QoS guarantees with TE. When ingress LSR establishes a tunnel to egress LSR, it sends a PATH message with inserted label to its next LSR. This LSR will then make a tempo- rary resource reservation and pass message on to the next node. On reaching an egress LSR, if this LSR can satisfy the resource request, it will then establish a tunnel and sends back the LABEL message with inserted label back to the ingress LSR, as the confirmation of resources and request of tunneling path [32].
  • 43. 43 4. Multi Protocol Border Gateway Protocol (MP- BGP) - BGP is a routing proto- col used to communicate between different autonomous systems. In the MPLS domain, it is used to set up virtual path between nodes across multiple au- tonomous systems. The ingress LSR uses BGP for distributing VPN routes to the egress LSR. BGP by itself does not distribute VPN routes, and so it needs differ- ent extensions to the protocol to provision this functionality, which is referred to as Multi-Protocol BGP (MP-BGP). When the ingress LSR wishes to establish a VPN route to an egress LSR, then this ingress LSR distributes the route to its next LSR through MP-BGP which then forwards the message to the particular adjacent node. 4.5 Network Recovery Models 4.5.1 Makam Model The Makam model, named after the author, is the first of its kind of network recovery introduced for the MPLS domain [33, 34]. The main idea behind this method is to setup end-to-end backup recovery path for any link/node failure. In the event of a failure, the FIS signal generated by a particular LSR is forwarded to the upstream ingress LSR. This ingress LSR is the same as PSL in this model. Figure 4.1 illustrates a network with the Makam recovery model. The protection switch path is a pre-computed backup path; PSL receiving the FIS signal through Reverse Notification Tree reroutes traffic from the working path to the backup path. Dynamic Rerouting is created once PSL receives the FIS signal. In general, the protection switch path is used since the service restoration time is less than that by using dynamic rerouting. In this model a global recovery scheme is adopted, implying that the node upon detecting a failure sends the FIS signal back to the ingress LSR to reroute traffic to PML or the egress LSR.
  • 44. 44 Working Path PGW-1 PGW-3 PGW-5 PGW-7 FIS PGW-0 Traffic Signal Phasor Gateway Router Rerouted PGW-9 PGW-10 PGW-2 PGW-4 PGW-6 PGW-8 Backup Path Figure 4.1 Makam model. 4.5.2 Haskin Model Haskin proposed a reverse backup path [35]. The key idea in this model is to reroute traffic back to PSL in case of a node/link failure. Upon detecting a link/node failure, the LSR which detects the failure sends incoming traffic back to ingress LSR or PSL, instead of sending FIS as in the Makam model. The major advantage of this model is the low number of packet dropped since no FIS needs to be sent to PSL, and rerouted traffic is inferred as a notification signal of the link/node failure to the ingress LSR. The disadvantage of this approach is inefficient resource utilization since in general the backup recovery path is longer than the original working path. Figure 4.2 shows how the Haskin model works. When a link between PGW-5 and PGW-7 is down, PGW-5 will send the traffic back to PGW-1. Upon receiving the transmitted traffic, PGW-1 becomes aware of the link failure in the working path. PGW-1 then switches traffic from the working path to the global recovery path.
  • 45. 45 Working Path PGW-1 PGW-3 PGW-5 PGW-7 Rerouted Traffic PGW-0 Phasor Gateway Router PGW-9 PGW-10 PGW-2 PGW-4 PGW-6 PGW-8 Backup Path Figure 4.2 Haskin model. 4.5.3 Hundessa Model Hundessa proposed a model [36] that offers better functionality as compared to the Haskin model. In the Haskin model, the PSL which reroutes traffic from the original working path to the global recovery path causes packet disordering at the egress LSR. Hence, Hundessa proposed an idea of buffering new packets until packets received from LSR, which detects the failure are rerouted to the global recovery path. The first packet received back from LSR which detects the failure is tagged, and hence all subsequent packets are tagged. Once all tagged packets are rerouted to global recovery path, all the buffered packets are then rerouted to the global recovery path, and thus avoiding packet disordering at the egress LSR. Figure 4.3 shows the Hundessa model in which PGW-5, which detects the link failure, reroutes the traffic back to the ingress LSR i.e., PGW-1. On receiving the packets at PGW-1, they are tagged and rerouted first on the global recovery path. At PGW-1, new traffic is first buffered until all tagged packets are rerouted. The advantage of this scheme is that it saves the processing time at the egress LSR of reordering packets.
  • 46. 46 Working Path PGW-1 PGW-3 PGW-5 PGW-7 Rerouted Traffic PGW-0 Phasor Gateway Router PGW-9 PGW-10 PGW-2 PGW-4 PGW-6 PGW-8 Backup Path Figure 4.3 Hundessa model. 4.5.4 Local Protection Model In this model, the LSR, which detects the link/node failure, calculates the new routing path to the egress LSR [31, 37, 38]. This model has the advantage of not requiring resource reservation. Also, it does not require pre-computing the global recovery path. However, this model is not suitable for time sensitive applications since new routes to egress LSR are calculated dynamically, and the number of packets dropped are more due to dynamic route selection. Figure 4.4 shows how local rerouting works. When PGW-5 detects the link failure between PGW-5 and PGW-7, it will start searching for a new path to egress PGW-9. This is done by pruning PGW-7 from the local copy of the network, and calculating the new shortest path to egress PGW-9.
  • 47. 47 Working Path PGW-1 PGW-3 PGW-5 PGW-7 PGW-0 Phasor Gateway Router PGW-9 PGW-10 PGW-2 PGW-4 PGW-6 PGW-8 Figure 4.4 Local Protection model. 4.5.5 Fast Reroute One of the major driving forces for MPLS is its capability to quickly reroute traffic and achieve service quality like SONET network with minimal service disruption time. In this model, the point of failure detection is the same as the point of repair, and thus it quickly reroutes traffic without sending the FIS signal or recalculating the new reroute path upon detecting a network failure [36]. According to IETF, many fast reroute techniques have been proposed, but the most commonly used technique is link protection In this technique LSP tunnel is setup to provide a backup path for the working path. When a link fails, the immediate node quickly switches traffic to the backup path with minimal disruption in service. The selected backup path should have similar bandwidth as that in the working path for all LSPs. If not, it should have sufficient bandwidth for LSPs to carry high priority traffic. In fast reroute, two types of labels are used. MPLS generated label is encapsulated into the physical layer label. In case a link is broken, packets are rerouted on to the backup path according to the physical layer label. Once packets reach the egress LSR or PML, the physical layer label is stripped down and packets are forwarded
  • 48. 48 according to the MPLS generated label. Figure 4.5 shows how fast reroute works. Working Path PGW-1 PGW-3 PGW-5 PGW-7 Pre-computed backup paths PGW-0 Phasor Gateway Router PGW-9 PGW-10 PGW-2 PGW-4 PGW-6 PGW-8 Figure 4.5 Fast Reroute with link failure.
  • 49. CHAPTER 5 SIMULTION RESULTS 5.1 Topology By the year 2013, Wide Area Monitoring System (WAMS) will consist of thousands of PMUs for the grid monitoring. It is worth iterating that all the PMUs will be connected across a WAN of nearly 150 PGWs (control centers). For simulation purposes, instead of taking into account of all the 150 PGWs, a set of 25 PGWs was taken under consideration for studying the conditions of the grid. The reason behind selecting only 25 nodes is that it is unlikely to reroute power from a rather remote plant. For instance, in case of a power outage in some parts of the New York, it is very unlikely that power will be rerouted from the power plants in California or Texas. This will result in improper resource utilization BRITE [37], a random topology generator, was used and modified to generate various network topologies This topology generator yields link latency in the order of 10s of milliseconds, which is unacceptable for Smart Grid monitoring. Often, the distance between two control centers lies in the range of 250-1000 miles, and thus the maximum permissible link latency is about 4-16 milliseconds. This conclusion is drawn from the fact that in a fiber link data travels at nearly 2/3rd of the speed of light. It is worth to mention that Los Angeles Department of Water and Power (LDWP) and Bonneville Power Administration (BPA) are the two control centers that are 1000 miles apart.. 49
  • 50. 50 Figure 5.1 Topology of 25 PGWs (nodes). 5.2 Simulation Setup Generally, every PMU maintains a dedicated telephone link to a single PDC. It is assumed that each PDC will have nearly 150 - 250 PMUs directly attached to it. Also, it is assumed that each PDC will maintain a dedicated fiber link to connect to a single PGW. Thus, every single PGW will be sending Constant Bit Rate (CBR) packets over UDP/IP. Data generated from each PMU will depend on the level of granularity needed for monitoring, and thus higher granularity level requires higher number of frames per second. According to the IEEE standard for phasor technology C-37.118, one frame is 128-byte long, and hence the minimum amount of bandwidth required between a PMU and PDC is 128 bytes/sample * 30 sample/second, i.e., 30.72Kbps. Table 5.1 shows the
  • 51. 51 minimum and maximum amount of bandwidth required between any two consecutive PGWs. Table 5.1 Required bandwidth between consecutive PGWs Data rate Frames per second 30fps 60fps 120fps 250fps # of PMUs 1 30.72Kbps 61.44Kbps 122.8Kbps 256Kbps 150 4.608Mbps 9.216Mbps 18.432Mbps 38.4Mbps 250 7.68Mbps 15.36Mbps 30.72Kbps 64Mbps The NS2 simulator was used to simulate the Smart Grid monitoring; it is the most widely used and trusted network simulator in the research community. NS2 is an event driven network simulator that was created with the joint effort among University of California – Berkley, Xerox PARC, University of Southern California, and Lawrence Berkeley National Laboratory. It is an object oriented simulator written in C++, and OTcl languages. While C++ acts as a back end running the actual simulation, OTcl works at the front end, and takes in user input to create and configure a network. C++ is used for faster computation and OTcl for ease of creating simulation scenarios. The default signaling protocol of the NS2 package is LDP, which is an obsolete protocol due to capability of modern routers to process IP headers at "wire speed". The most common signaling protocol for MPLS applications is RSVP-TE due to its unique feature of allocating bandwidth efficiently, but since Table 5.1 concludes that
  • 52. 52 bandwidth is not a constraint for Smart Grid monitoring purpose, hence it was not used for simulations. For the present simulation work, the CR-LDP protocol was chosen, since it allocates bandwidth without requiring to reserve the resources for any kind of application, thus less requiring less overhead compared to RSVP-TE and most suitable for Smart Grid applications. Since the ns2 package does not contain MPLS module with CR-LDP signaling, so the source code from [38, 39] were adopted for simulating network recovery models. Figure 5.2 and 5.3 show the service disruption time and number of packets dropped, due to a link failure. In comparing Figure 5.2 and Table 2.3, it can be concluded that, for time critical applications, fast reroute is the most suitable network recovery model. Table 5.2 summarizes the required network recovery models for different class of services. 18 15 12 9 6 3 0 Makam Haskin Local Protection Fast Reroute Figure 5.2 Service disruption time for different MPLS models.
  • 53. 53 60 50 40 30 20 10 0 Makam Haskin Local Protection Fast Reroute Figure 5.3 Number of packets dropped for different MPLS models. Table 5.2 Suggested Network Recovery Models for Different Class of Service Class Description Availability (%) Network of Service Recovery model A Feedback Control, 99.9999 Fast reroute Situational awareness, event triggering B Feed forward control 99.999 Makam, or Hundessa C Display 99.99 Local protection D Disturbance analysis 99.99 Local protection E Research 99.99 Local protection
  • 54. CHAPTER 6 CONCLUSION Smart Grid will be evolving from existing power grid to modern, reliable, secure and green grid. NIST and DoE, along with CERTS, NASPInet, NERC, and EIRP, will be playing crucial roles for this grid modernization; they are still under initial stages of finalizing Smart Grid frameworks and roadmaps. By the end of year 2010, NIST has planned to complete all the priority action plans, like guidelines for IP protocol suite and wireless communications, and standard meter data profile. This thesis has proposed a solution to one of the major challenges of Smart Grid, i.e., real time grid monitoring and control. MPLS is proposed to realize WAMS, owing to the support of packet encapsulation, VPN, QoS and real time communications. Most importantly, it was demonstrated that it provisions the required network recovery models which can further be used for different classes of services proposed by NASPInet. Based on the simulation results, the Fast Reroute model is appropriate for applications like feedback control, situational awareness, state estimation, and early event detection, although each link has to maintain a separate recovery path in this model. This overhead is nevertheless well justified for such a critical network. 54
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