International telecommunication union

səhifə	5/8
tarix	27.06.2016
ölçüsü	3.68 Mb.

1 2 3 4 5 6 7 8

8 Deployment Model of Smart Grid

This section focuses on development and implementation models for smart grid network.

8.1 Networks in Smart Grid

In order to describe the architecture of smart grid communication networks, the smart grid network can be categorized into several logical components based on their coverage, such as Home Area Network, Local Area Network, Neighbourhood Area Network, Wide Area Network, and Access Network. This does not imply that physical implementation must divide the network this way, nor that network companies must structure their network in a similar way and limit their services to some specific components. The general meaning of these components is listed in Table 1. Note that the areas covered by these components may overlap, but should be obvious in the context being discussed.

Table 1: Major Components of Smart Grid Networks

Term	Definition
Wide Area Network	A wide area network (WAN) is a communication network that covers a wide geographical area and accommodates terminals and LANs. This is typically called “Back Haul” network in smart grid environment.
Local Area Network	A local area network (LAN) is a network that connects computers and devices in a limited geographical area such as home, computer laboratory, office building, and closely positioned group of buildings.
Home Area Network	In the smart grid applications, Home Area Network (HAN) refers to the networks in the homes that interconnect energy devices, including appliances, energy management station, plug-in electrical vehicle chargers, energy sources.
Access Network	An access network refers to a network which connects subscribers to their immediate service provider (ISP). It is contrasted with the core (or transport) network in wide area network.
Neighborhood area network (NAN)	Neighborhood area network (NAN), is an access network that allows smart grid end-device and home area networks to connect to wide area network.

8.2 Smart Grid Network Architecture

8.2.1 Home Area Network Architecture

This section provides additional descriptions of the Home Network Function group in the End-User Functions group. While in Section 7.2.1.1, the major functions of HAN are discussed, the issues related to the architecture of HAN or the physical connections within a HAN will be focused here.

8.2.1.1 HAN Topology

Within a HAN, there are many ways to interconnect devices in a home, depending on the physical medium and communications protocol to be used. As shown in Figure 7, possible topologies in a HAN include:

Bus Topology: As shown in Figure 7(a), all devices in a bus topology share a common transmission medium. An example is the use of power lines or coaxial cables.
Tree Topology: As shown in Figure 7(b), all devices in a tree topology are connected to a central “root” node in a tree fashion. A Wi-Fi access point communicating with IEEE 802.11 devices is an example of a tree topology; and a simple router used in home that connects devices using twisted pair cables is another example. It is possible to cascade stars into hierarchy of stars like tree branches.
Mesh Topology: As shown in Figure 7(c), devices interconnect in a meshed network. Each node participates in maintaining communications with its neighbours and routing message toward their destinations. This topology is typically used in wireless network when reliability and connectivity is needed.

Figure 7: Possible topologies of HAN

In a home environment, one or more of these topologies may be used, as a single transmission medium or communication technology may not provide sufficient coverage, due to wiring constraints and environmental factors. Therefore, interconnecting devices into a network and routing message among these devices with minimum human intervention are major issues in designing HAN architecture.

8.2.1.2 Energy Service Interface (ESI)

The Energy Services Interface (ESI) function block in the End-User Functions provides data transfer for devices in HAN, and interface to the Utility network through the Neighbourhood Area Network that provides the Metering data exchange Function in the Network Functions block. The implementation may consist of one or more physical devices; it could even be an integrated part of smart meters. The ESI satisfies the “gateway” requirement as described in the Requirement Deliverable.

The functions of ESI on the HAN include:

Provide interfaces to support the transmission medium used in HAN, wired or wireless, in order to provide connectivity to all devices supporting End-User Functions.
Provide message routing capability to allow exchange of information between devices. This could be implemented as OSI layer 2 bridging or layer 3 routing. This function is essential in enabling the Home Energy Management Function block to communicate, manage, and control energy devices in a home.
Provide message filtering capability to ensure the integrity of the Utility network. The filtering is carried out in the way that only a certain outgoing messages from HAN are permitted to go across the HAN, NAN, or WAN boundaries.
Perform HAN device configuration and management. The ESI works with the Home Energy Management Function block and Security Functions block as well as the Customer Subscription and Billing function in the Application Functions block to manage joining and departure of devices in HAN, to authenticate the validity of these devices, and to determine their privileges in exchange of information.

On the NAN side, the ESI provides external connection to rest of Utility network for:

Access to the metering information,
Exchange information for the Demand Response Function.

8.2.1.3 Interactions with Other Networks

In the context of this deliverable, the term HAN refers to the home portion that connects with the Utility network, which is defined in Section 7.2.1.1. However, networks in homes very often have many uses, such as residential broadband for PCs or entertainment devices, and may have connections to non-utility networks such as Internet from Telecommunications Companies or Internet Service Providers (ISP) as depicted in Figure 8 below. The diagram on the right is the Customer Domain portion of the reference architecture in Figure 2 of the Smart Grid Overview deliverable; the circled part shows multiple connections from a customer domain to the outside world. The diagram on the left of Figure 8 shows how such home networks, consisting of a utility HAN and a residential broadband network might be configured; the two entities could be physically separate networks, or the utility HAN could be a logical subnet within the home network. Therefore, how one architect the utility portion of a home network, or Utility HAN, has profound impact to the security of the Smart Grid. In both cases, security issues must be addressed to ensure the integrity and reliability of the Smart Grid utility network. Note that the arrow between ESI and Router on the left of Figure 8 implies communication path between ESI and a third party through the router.

Figure 8: A Home with Multiple Networks and Connections to

Utility Network and Other External Networks
The architectural design of customer premises networks could address the security issues in the following ways:

When the utility HAN is physically separate from the residential broadband network, an ESI or a gateway with additional functions of an ESI could be used to interconnect the two networks so that limited information could be exchanged.
When the two networks are not physically separate from each other, a configuration manager could be used to make the Utility HAN a logically sub-network such that nodes in the sub-network has special privileges in accessing the Utility Network. The privileges may be in multiple classes.
Detailed security functions of an ESI are described in Section 8.2.1.2 Energy service interface.
Proper encryption and signature mechanisms are used to maintain the authenticity and integrity of messages transfer end-to-end between Application Functions group and nodes in the Utility HAN.

8.2.2 Neighborhood Area Network Architecture

The Neighborhood Area Network performs the Metering Data Transport Function shown in Figure 4 for Functional Model and provides connectivity for meters in a small geographical area, data aggregation for meter readings, and connectivity for the homes through the ESI function. The metering information are aggregated and forwarded through the Wide Area Network to the Smart Meter Head-Ends. The information for the Demand Response Application Function communicated with the Home Energy Management Function in the End-User Functions block through WAN, NAN, and HAN.

8.2.2.1 NAN Topology

In a neighbourhood area, the environmental factors affecting the performance of communications network such as geographical topology, the density of buildings, and the external signal interference are major considerations for developing the architecture of the NANs. There are potentially two different network topologies as shown in Figure 9.

Tree Topology: As shown in Figure 9(a), each ESI as a “leaf” node has a point to point link with the upper level Collector as a “root” node.
Mesh Topology: As shown in Figure 9(b), each ESI has point to point connection with other ESIs or other NAN nodes in the network. This is used in a wireless environment to enhance the reliability and resilience of communication paths, and to extend coverage area that one collector supports.

NAN topologies are described according to the following three functionalities.

ESI Function: This function is described in Section 8.2.1.2 “Energy service interface (ESI).” In the NAN topology models, ESI function terminates NAN communication link at HAN side. ESI may have routing functions to form a full-mesh topology, or may only have simple forwarding function to communicate with few specific nodes in a tree topology.
Collector Function: This function is one of an AMI function referred to in IETF RFC6272. In the NAN topology models, Collector function terminates NAN communication link at WAN side. Collector function may aggregate data from underlying Collectors, Relays and ESIs, and de-aggregate data to underlying Collectors, Relays and ESIs.
Relay Function: This function is a routing function to form a NAN full-mesh topology. Relay function works between Collectors and ESIs to control routing metrics for multi-hop mesh network. Relay function may be implemented separately to construct redundant networks or to cover wider area of neighbourhood. Relay function may also be implemented in ESI or Collector nodes.

(a) NAN Tree Topology (b) NAN Mesh Topology
Figure 9: Possible topology of NAN
In the NAN tree topology model, a collector is connected to one or more ESIs at HAN side, and to AMI Head-end at WAN side. Collector may also connect to other collectors to form a hierarchical tree topology as shown in the lower right side of Figure 9(a). A special case of tree topology is one-hop star topology as shown for the two ESIs on the left of Figure 9(a). Either wired communication or wireless communication is applicable to this model. A variety of link layer technologies can be used; for examples, power line communications, wireless technology such as IEEE family of wireless protocol and cellular network technologies can be used for the communication links between collectors and ESIs.

A type of NAN Mesh network where all possible links between nodes are selected for communication paths is called “Full-Mesh”. Full-Mesh works well but routing metrics and its control traffic become huge as the number of nodes in a network increases to a certain amount. Another routing method is many-to-one routing. Many-to-one routing is optimized to collect data from many points to one single point and is recommended in the large scale networks such as an AMI infrastructure. Figure 9(b) illustrates these two types of NAN mesh topology, where the left side is a Full-Mesh topology and the right side is Many-to-One topology. Note that there are multiple routes between some specific two nodes to form a mesh topology in Figure 9(b). In this case, data are forwarded through one of those routes.

The following two methods could be considered for relaying data in the mesh networks.

Layer 2 Forwarding: This is a method of multi-hop forwarding on data link layer. It can work effectively using control information and status in the data link layer and it can forward data efficiently without overhead of IP layer. This method is suitable for nodes with less CPU power and strong power-conscious.
IP Forwarding: This is a method of multi-hop forwarding on IP layer. Data is forwarded as IP datagram hop by hop in the mesh network where a routing protocol runs on the IP layer. This method is more suitable for relatively high-end nodes with enough CPU power and memories for IP router functions.

Note that IETF developed specifications for both methods (L2 forwarding aka mesh-under and IP forwarding aka route-over) while IEEE802 addressed L2 forwarding technologies [2].

Hierarchical mesh network should also be considered, especially where WAN connects to multiple multi-hop networks covering large geographical area like town as well as smaller neighbourhood area as shown in Figure 9(b).

8.2.3 Wide Area Network Architecture

The Wide Area Network (WAN) performs the Core Network Transport Function in the Functional Model shown in Figure 4. There are many different views on where the WAN begins and ends. In some countries, WAN includes all telecom company circuits and ends at the entrance to customers premises. To facilitate discussions of network architectures in this document, any networks beyond the NAN or the last metering information aggregation point belong to WAN.

8.2.3.1 IP-Based Network

A possible WAN architecture is an Internet Network utilizing the Internet Protocol suite, including session control, transport function, message routing, security functions, network management and many others, as described in RFC6272 [2], “Internet Protocols for the Smart Grid.” The following is a general description of Internet in this RFC.

“The Internet is a network of networks in which networks are interconnected in specific ways and are independently operated. It is important to note that the underlying Internet architecture puts no restrictions on the ways that networks are interconnected; interconnection is a business decision. As such, the Internet interconnection architecture can be thought of as a "business structure" for the Internet.

Central to the Internet business structure are the networks that provide connectivity to other networks, called "Transit Networks". These networks sell bulk bandwidth and routing services to each other and to other networks as customers. Around the periphery of the transit network are companies, schools, and other networks that provide services directly to individuals. These might generally be divided into "Enterprise Networks" and "Access Networks"; Enterprise networks provide "free" connectivity to their own employees or members, and also provide them a set of services including electronic mail, web services, and so on. Access Networks sell broadband connectivity (DSL, Cable Modem, 802.11 wireless or 3GPP wireless), or "dial" services including PSTN dial-up and ISDN, to subscribers. The subscribers are typically either residential or small office/home office (SOHO) customers. Residential customers are generally entirely dependent on their access provider for all services, while a SOHO buys some services from the access provider and may provide others for itself. Networks that sell transit services to nobody else - SOHO, residential, and enterprise networks - are generally referred to as "edge networks"; Transit Networks are considered to be part of the "core" of the Internet, and access networks are between the two.”
This general structure is depicted in Figure 10.

canvas 1669
Figure 10: Conceptual Model of Internet Businesses
It should be noted that the medium layer technologies mentioned above is not an exhaustive list, and there are other technologies and protocols that are equally applicable.

The Internet protocol suite is based on the protocol stack shown in Figure 11. This model is important as IP-based smart grid applications end-to-end exchange of information, is assuming certain services provided by the transport and network layer functions, and is independent of physical communication media used. This allows software designers to focus on application protocol and coding of information, thus simplifies the design task.

Application

Application Protocol
Encoding	Session Control

Transport

Transport layer

Network

Internet Protocol

Lower network layers

Media layers

Data Link Layer

Physical Layer

Figure 11: The Internet Protocol Stack Model

8.2.3.2 Next Generation Network Architecture

NGN services include multimedia services such as conversational services, and content delivery services such as IPTV services. In addition, key features of NGN such as fixed mobile convergence (FMC) support providing QoS and security play an important role in areas of smart grid applications. Figure 12 shows an overview of the NGN functional architecture, which is described in detail in ITU-T Y.2012 [8].

As described in ITU-T Y.2011 [7], the separation of services from transport, allowing them to be offered separately and to evolve independently, is the key cornerstone of NGN characteristics. The separation is represented by two distinct blocks or strata of functionality.

There is a set of transport functions that are solely concerned with conveyance of digital information, of any kind, between any two geographically separate points. A complex set of layer networks may be involved in the transport stratum, constituting layers 1 through 3 of the OSI 7 layer Basic Reference Model. The transport functions provide connectivity.

The services platforms provide the user services, such as a telephone service, a Web service, etc. The service stratum may involve a complex set of geographically distributed services platforms or in the simple case just the service functions in two end-user sites. There is a set of application functions related to the service to be invoked.

Figure 12 shows that the transport functions reside in the transport stratum and the service functions related to applications reside in the service stratum. The delivery of services/applications to the end-user is provided by utilizing the application support functions and service support functions, and related control functions. The transport stratum functions include transport functions and transport control functions. The transport stratum provides the IP connectivity services to the NGN users under the control of transport control functions.

Among interfaces specified in Figure 12, ANI (application network interface) and SNI (service network interface) are distinguished from each other. The ANI is an interface which provides a channel for interactions and exchanges between an NGN and applications. The ANI offers capabilities and resources needed for realization of applications. The ANI supports only a control plane level type of interaction without involving media level (or data plane) interaction. On the other hand, the SNI is an interface which provides a channel for interactions and exchanges between an NGN and other service providers. The SNI supports both a control plane level and media level (or data plane) type of interaction.

8.2.3.2.1 Transport Stratum

The transport functions provide the connectivity for all components and physically separated functions within the NGN. These functions provide support for unicast and/or multicast transfer of media information, as well as the transfer of control and management information. Transport functions include the followings:

Access Network Functions
Edge Functions: The Edge Functions are used for media and traffic processing when aggregated traffic coming from different access networks is merged into the core transport network; they include functions related to support for QoS and traffic control.
Core Transport Functions
Gateway Functions: The Gateway Functions provide capabilities to interwork with end-user functions and/or other networks.
Media Handling Functions: The Media Handling Functions provide specialized media resource processing for service provision, such as generation of tone signals and transcoding.

The transport control functions include the followings:

Resource and Admission Control Functions: The Resource and Admission Control Functions act as the arbitrator between service control functions and transport functions for QoS.
Network Attachment Control Functions: The Network Attachment Control Functions provide registration at the access level and initialization of End-User functions for accessing NGN services.
Mobility Management and Control Functions: The Mobility Management and Control Functions provide functions for the support of IP-based mobility in the transport stratum.

8.2.3.2.2 Service Stratum

The Service Stratum functions include Service Control and Content Delivery Functions, and Application Support Functions and Service Support Functions.

Service Control and Content Delivery Functions: The Service Control Functions include resource control, registration, and authentication and authorization functions at the service level, while the Content Delivery Functions receive content from the Application Support Functions and Service Support Functions, store, process, and deliver it to the End-User Functions using the capabilities of the transport functions, under control of the Service Control Functions.
Application Support Functions and Service Support Functions: The Application Support Functions and Service Support Functions include functions such as the gateway, registration, authentication and authorization functions at the application level. These functions are available to the "applications" and "end-user" function groups.

8.2.3.2.3 Identity Management (IdM) Functions

ITU-T Y.2012 [8] describes that IdM Functions and its capabilities are used to assure the identity information, assure the identity of an entity and support business and security applications (e.g., access control and authorization), including identity-based services. An entity is considered to be anything that has separate and distinct existence that can be uniquely identified.

In the NGN environment, a single entity may be associated with multiple types of identity information which can be grouped as follows:

Identifiers: UserID, email addresses, telephone numbers, URI and IP addresses, and others.
Credentials: Digital certificates, tokens and biometrics, and others.
Attributes: Roles, claims, privileges, patterns and location, and others.

Figure 12: NGN Architecture Overview

8.2.3.3 Consideration of the M2M Service Layer aspects

When considering Smart Grid as one of the various specific M2M applications, telecommunication aspects at the service layer can be addressed in an optimized way by taking benefit of the functional architecture specified by [3] through standardized Service Capabilities (SCs), as shown in Figure 13.

M2M Service Capabilities provide M2M functions that are to be shared by different Applications. These functions, implemented at the Service Layer in M2M Devices / M2M Gateways and in the Network server, are exposed through a set of open interfaces.

Figure 13: High Level Architecture with ETSI M2M Service Capabilities Layer

These SCs, using the ETSI M2M terminology, are partly described below for specific use by the Smart Grid applications. For more details on these SCs and how to implement them, refer to ETSI M2M specifications [3, 4].

The “Generic Communication” SC (in the Device / Gateway / Network) for the communication between Network Service Capability Layer (SCL) and Gateway SCL (or Device SCL) to enable delivery of the M2M Service corresponding to the Power Grid Functions;
The “Telco Operator Exposure” SC (in the Network) is an optional SC that can be used for interworking purposes with existing telecommunication networks that could be involved in the Power Grid Functions;
The “Communication Selection” SC (in the Device / Gateway / Network) to ensure that there is a new network selection to exchange information for the Power Grid Functions in case of failure of the one initially used;
The “Reachability, Addressing and Repository” SC (in the Device / Gateway / Network) to be kept informed on the status of the entities involved in the Power Grid Functions;
The “Remote Entity Management” SC (in the Device / Gateway / Network) provides the Management functions also involved in the functional model of Smart Grid illustrated in Section 7;
The “Interworking Proxy” SC (in the Device / Gateway / Network) is an optional SC to provide interworking between non ETSI compliant devices or gateways and the Network SC Layer through an mId compatible reference point; in smart grid applications, this can be used for the smart meter to be M2M-enabled for example;
The “Compensation Brokerage” SC (in the Device / Gateway / Network) is an optional SC used where a Broker acts to submit compensation tokens (i.e. electronic money) to requesting Customers and to bill the customer of compensation tokens for the amount spent, before redeeming Service Providers for tokens acquired as compensation for services provided to customers;
The “Application Enablement” SC (in the Device / Gateway / Network) is the single contact point between the SCLs and the M2M Applications;
The “SECurity” SC (in the Device / Gateway / Network) performs Security Functions also involved in the functional model of Smart Grid as illustrated in Section 7;
The “History and Data Retention” (in the Device / Gateway / Network) is an optional SC, deployed when needed by the Service Capability Layer provider. It is used to archive relevant information pertaining to messages exchanged over the reference point and also internally to the SCL.

All these Service Capabilities are exposed to the M2M applications (including Smart Grid applications) through the following reference points, and those are specified by [4].

mIa Reference Point: allows a Network Application (NA) to access the M2M Service Capabilities in the Network Domain.

dIa Reference Point: allows a Device Application (DA) residing in an M2M Device to access the different M2M Service Capabilities in the same M2M Device or in an M2M Gateway, and also allows a Gateway Application (GA) residing in an M2M Gateway to access the different M2M Service Capabilities in the same M2M Gateway.

mId Reference Point: allows an M2M Service Capabilities residing in an M2M Device or M2M Gateway to communicate with the M2M Service Capabilities in the Network Domain and vice versa. mId uses core network connectivity functions as an underlying layer.

1 2 3 4 5 6 7 8