KR20020061826A - Method of controlling management for network element integration on communication system - Google Patents

Abstract

PURPOSE: A method for controlling and managing for network element integration in a communication system is provided to remove RP connection between a PCF and a PDSN, thereby making a virtual link set and GRE protocol unnecessary. CONSTITUTION: A PCF(Packet Control Function) sends a mobile IP registration request message(401). An FAC(Foreign Agent Controller) extracts an NAI(Network Access Identifier) from the received mobile IP registration request message and searches the corresponding database based on the NAI for confirming authentication completion(402,403). If an authentication is already confirmed, the FAC creates the mobile IP registration request message omitting an authentication procedure and transmits the message to a mobile IP home agent(406). If the authentication is initially tried, an authentication message is created and transmitted to an AAA(Authorization Authentication Accounting) server(404). If the AAA server sends an authentication acknowledgement message, the FAC updates database with authentication completion(405). The FAC creates a mobile IP registration request message for transmitting to the mobile IP home agent(406). If the mobile IP home agent sends a mobile registration response message, the FAC transmits the message to a mobile station(407,408).

Description

Method of controlling management for network element integration on communication system

The invention ^{3GPP2 (3 rd Generation Partnership Projects-} 2) IMT-2000 (International Mobile Telecommunication), UMTS efficient network structure, etc. (Universal Mobile Telecommunication Service) next-generation mobile communication network-based integrated Internet Protocol (ALL-IP) networks, such as and A control management method for integrating network elements such as a packet control function (PCF) and a packet data serving node (PDSN) function to provide a data service function, and to realize the method. A computer readable recording medium having recorded a program.

1 is a configuration example of a conventional network, ^{3GPP2 (3 rd Generation Partnership Projects-} 2) Fig.

Radio Access Network (RAN) 12 is composed of a Base Station Controller (BSC) and a Base Station Transceiver Subsystem (BTS), and a Visitor Location Register (VLR) ( 13) and a home location register (HLR) 14 provides mobility management and authentication of a mobile station (MS) 11.

When the basic authentication of the data call is completed, the radio access network (RAN) 12 establishes a virtual connection for the packet data service node (PDSN) 16 and the Generic Routing Encapsulation (GRE) protocol.

The Packet Data Service Node (PDSN) 16 establishes a Point-to-Point Protocol (PPP) connection with the MS 11 and establishes a Remote Authentication Dial In service. User service) transmits subscriber authentication and billing information through server.

When providing a mobile IP service, the packet data service node (PDSN) 16 performs a foreign agent (FA) function, and is a home agent (HA) 15 existing in the home network of the mobile station IP address. ) Performs functions such as location information management and tunnel setup for mobile IP.

As such, the conventional packet control function (PCF) is an interworking system of a radio access network (RAN) 12 for interworking with a packet network, and the packet data service node (PDSN) 16 is a radio access network (RAN) ( 12), it functions as an access node for connecting the data subscriber connected through the packet network to the packet network, and the radio access network (RAN) 12 and the packet network are completely separated.

However, in the future, 3GPP2 network or ALL-IP network is evolving the whole into one IP network, and existing base station controller (BSC), packet control function (PCF) and packet data service node (PDSN) are connected to one wireless network. It is viewed as a system called a gateway device (WAG: Wireless Access Gateway). Accordingly, access nodes of data subscribers are increasingly being moved to the lower level of the network as they are integrated into a single wireless access gateway (WAG).

In particular, in the IMT-2000 network and the All-IP network structure being standardized in 3GPP2, the system of the packet control function (PCF) and the packet data service node (PDSN), as shown in Figs. exist.

The packet control function (PCF) may exist inside a base station controller (BSC) system or may be implemented as a separate system. However, most developers implement an independent system to provide effective mobility in a mobile network.

The packet control function (PCF) and the radio access network (RAN) called "RP Interface" (RP Interface) for connecting the data of the mobile station (MS) transmitted from the radio access network (RAN) to the packet data service node (PDSN) It uses the connection method between packet data networks (PDN) and tunnels through the GRE protocol encapsulation and decapsulation of user-specific virtual link connection and user data for data transmission in RP connection. Tunneling) function. In addition, a buffer function and a packet segmentation function that allow link layer packets to be transmitted to an air interface to be transmitted to a mobile station (MS) received from a packet data service node (PDSN). ) Perform the function.

The Packet Data Service Node (PDSN) performs PPP / GRE protocol processing to process packets received from the Packet Control Function (PCF). At this time, when the packet control function (PCF) and the packet data service node (PDSN) exist in different systems, there are the following problems.

First, the delay in transmission of user packets of mobile terminals (MS) is increased compared to the integrated system. This is because each time it goes through the network element, it goes through a Store and Forward process.

Second, since the current PDSN handles both control and bearer, in case of a failure, all session-related information is lost and resource management is performed when hand-off. Inefficient

Third, inefficiency of data transmission due to header overlap of GRE / PPP in RP connection. In particular, when the connection layer end of the mobile terminal (MS) is in the packet data service node (PDSN) in the process of evolving to IPv6 (HA) in the future, the RP connection must adhere to the tunneling method of IPv4 (GFA). Therefore, in the future evolution to IPv6, it is reasonable to handle the connection layer protocol of the mobile terminal (MS) of the packet data service node (PDSN) in the packet control function (PCF).

As described above, in order to interwork with a radio access network (RAN) and an IP network in the 3GPP2 IMT-2000 network, a packet control function (PCF) is required in the radio access network (RAN), and in the IP network, a packet data service node (PDSN) Was required. Therefore, in order to provide efficient network structure and data service function in IMT-2000 network and ALL-IP network, a control management plan that can integrate packet control function (PCF) and packet data service node (PDSN) functions is essential. Required.

The present invention has been proposed to meet the above-mentioned requirements, and provides a packet control function (PCF) and a packet to provide an efficient network structure and data service functions in a next generation mobile communication network-based integrated Internet protocol (ALL-IP) network. It is an object of the present invention to provide a control management method for integrating network elements such as a data service node (PDSN) function and a computer-readable recording medium recording a program for realizing the same.

1 is a configuration example of a conventional network, ^{3GPP2 (3 rd Generation Partnership Projects-} 2) Fig.

2 is an exemplary configuration diagram of a 3GPP2 Integrated Internet Protocol (ALL-IP) network to which the present invention is applied.

3 is an exemplary protocol configuration of a packet control function (PCF) having a mobile IP external agent (FA) function according to the present invention.

4 is a flowchart of an embodiment of a control management method according to the present invention;

* Explanation of symbols for the main parts of the drawings

201: Wireless Access Gateway (WAG) 202: Authorization / Authentication / Charging (AAA) Security Manager

203: home location register (HLR) 204: existing service support function

205: location server 206: media gateway device

207: media gateway device control function unit 208: media resource function unit

209: Mobile IP Home Agent 210: Mobility Manager

211: Policy Manager 212: Resource Manager

213: roaming signal gateway device 214: service generation environment function

215: service manager 216: session manager

217: relay signal gateway device 218: home subscriber server

The present invention for achieving the above object, in the control management method for network element integration in the integrated Internet Protocol (ALL-IP) network based on the next-generation mobile communication network, packet control for interworking a radio access network (RAN) to a packet network A packet data service node (hereinafter referred to as "PDSN") that performs a function (hereinafter referred to as "PCF") and a connection node for connecting a data subscriber connected through the radio access network (RAN) to the packet network. Function to integrate the mobile internet protocol (hereinafter referred to as " mobile IP ") service to the PCF by integrating the PDSN's mobile IP external agent (FA) function and the mobile terminal's link layer termination function; First step; When requesting mobile IP registration from the mobile terminal, an external agent controller (hereinafter referred to as " FAC ") that manages a plurality of PCFs extracts subscriber identification information from the mobile IP registration request message received through the PCF in a database. A second step of searching for an existing authentication; A third step of transmitting a mobile IP registration request message directly to a home agent (HA) without performing authentication again in accordance with the search result of the second step; And a fourth step of notifying the mobile terminal of the received mobile IP registration response message when the mobile IP registration response message is received from the home agent HA.

In addition, the present invention transmits the authentication message to the authentication server at the time of the first authentication, the search result of the second step, and when the authentication completion from the authentication server is updated in the database, the home agent (HA) Transmitting a IP registration request message to a mobile station; And a sixth step of notifying the mobile terminal of the received mobile IP registration response message when the mobile IP registration response message is received from the home agent HA.

In order to achieve the above object, the present invention provides a communication system including a processor for interworking a radio access network (RAN) to a packet network for control management for network element integration in an integrated internet protocol (ALL-IP) network. A packet data service node (hereinafter referred to as "PDSN") that performs a packet control function (hereinafter referred to as "PCF") and a connection node for connecting a data subscriber connected through the radio access network (RAN) to the packet network. Integrate the "one" function into one, but integrate the PDSN's mobile IP external agent (FA) function and the mobile terminal's link layer termination function to the PCF when providing a mobile Internet protocol (hereinafter referred to as "mobile IP") service. A first function of accommodating; When requesting mobile IP registration from the mobile terminal, an external agent controller (hereinafter referred to as " FAC ") that manages a plurality of PCFs extracts subscriber identification information from the mobile IP registration request message received through the PCF in a database. A second function of searching for an existing authentication; A third function of transmitting a mobile IP registration request message directly to a home agent (HA) without performing authentication upon pre-authentication according to the search result of the second function; And a computer-readable recording medium having recorded thereon a program for realizing a fourth function of notifying the mobile terminal of the received mobile IP registration response message upon receiving a mobile IP registration response message from the home agent HA. do.

Further, the present invention transmits an authentication message to the authentication server at the time of initial authentication according to the search result of the second function, updates the authentication completion fact to the database at the completion of authentication from the authentication server, and then the home agent ( A fifth function of sending a mobile IP registration request message to HA); And a computer-readable recording medium having recorded thereon a program for realizing a sixth function of notifying the mobile terminal of the received mobile IP registration response message upon receiving a mobile IP registration response message from the home agent HA. to provide.

The present invention provides a link layer of a mobile terminal (MS) and a mobile IP external agent (FA) function of a PDSN in a PCF in a system of a separate type of a packet control function (PCF) and a packet data service node (PDSN) function. Efficient mobile communication data service can be provided by facilitating network configuration in future evolution to ALL-IP network by reducing termination function, reducing delay of data transmission, and controlling control plane as a separate network element. Make sure

The above objects, features and advantages will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

2 is an exemplary configuration diagram of a 3GPP2 integrated internet protocol (ALL-IP) network to which the present invention is applied.

The wireless access gateway device (WAG) 201 is for interworking the existing base station controller (BSC), packet control function (PCF), packet data service node (PDSN) function, etc. into a single system, a radio controller, voice and data Perform gateway functions and more.

A base station controller (BSC) controls and manages one or more base stations (BTSs), and performs traffic and signaling, mobility management, and mobile terminal (MS) management related to call processing. Radio access network (RAN) is composed of a base station controller (BSC) and a base station (BTS).

The packet control function (PCF) may exist inside a base station controller (BSC) system or may be implemented as a separate system outside. The packet control function (PCF) may include data of a mobile terminal (MS) transmitted from a radio access network (RAN). PDSN).

The packet data service node (PDSN) performs an external agent (FA) function, delivers incoming and outgoing packets for packet data of the mobile station (MS) to an appropriate path, and establishes and manages a connection layer protocol of the mobile terminal (MS). Plays an end role.

Authorization / Authentication / Charging (AAA) The security manager 202 provides Internet protocol functions that support authentication, authorization, and billing functions.

The home location register (HLR) 203 has information such as subscriber information, IP priority, resource and authority usage for interdomain service, and the like.

The legacy service support unit 204 manages functions such as call processing, mobility management, resource management, security management, and service management, which were provided by the existing line-type wireless network.

The location server 205 has location information, a function such as a mobile location center, and a function of position measurement equipment (PDE).

The media gateway 206 performs functions such as protocol and address translation when the user's data is transferred to a public data network or another network.

The media gateway control function 207 controls and manages the media gateway devices 206.

The media resource function 208 performs a management function of allocating / releasing resources of the media gateway devices 206.

The Mobile IP Home Agent 209 manages the IP address of the external agent as a table of the location information of the mobile IP as a table, and transmits the transmission data to the subscriber through tunnel and encryption as necessary. Perform.

The mobility manager 210 performs a handoff management function between the radio access gateway devices 201 or between networks.

The Policy Manager 211 manages policy data and rules and allows interaction with various policies.

The resource manager 212 manages resources necessary to provide a service to a network user.

The roaming signaling gateway 213 performs a function of converting packet signals into a signaling scheme of a circuit switched network or a signaling scheme of a circuit switched network into packet signals.

The service creation environment function unit 214 provides an operator with an environment in which new services and application services can be created.

The service manager 215 manages network authentication and all voice and data service logic.

Session Manager 216 establishes and manages sessions, states, and handoffs across multiple networks.

The trunk signal gateway 217 performs a function of converting the signaling method of the public switched telephone network (PSTN) and the signaling method of the core network.

A home subscriber server (HSS) 218 includes at least network elements such as AAA, HLR, EIR, LOC, UMS, and the like.

The Equipment Identity Register (EIR) is a database (DB) for device information.

The location related information DB (LOC) provides location related information required by the location server 205.

The Policy Repository stores data on subscribers, multimedia usage policies, quality of service, validity time and route.

The protocol structure for accommodating the mobile IP external agent (FA) function of the packet data service node (PDSN) in the packet control function (PCF) is shown in FIG.

Referring to FIG. 3, a User Datagram Protocol (UDP) processing unit 304, an Internet Protocol (IP) processing unit 305, an Internet Protocol encryption (IPsec) unit 309, and an end-to-end protocol ( The PPP: Point to Point Protocol (PPP) processing unit 306 conforms to a protocol defined by the Internet Engineer Task Force (IETF), and the link layer 307 is an asynchronous transfer mode or an Ethernet.

The base station controller interworking signal processing unit 301 is in charge of the A9 interface of ISO 4.0 (control standard related to the control of the base station controller (BSC) and the packet control function (PCF)) interface of ISO 4.0, and the data call related call received from the base station controller (BSC) Process various signals related to processing and resource management.

Authorization / Authentication / Charging (AAA) Protocol The client processing unit 302 performs authentication for accessing the IP network of the mobile terminal (MS) through the authorization / authentication / charging protocol, and authorizes / authenticates / charges the billing information generated in the system. It performs the function of forwarding to the AAA security manager 202.

The mobile IP external agent function processing unit 303 is a function block for processing messages related to the mobile terminal MS and the mobile IP, and manages a visitor list. This establishes tunneling with the mobile IP home agent 209 and, if necessary, also encrypts the IP.

Looking at the main functions of the packet control function (PCF) to accommodate the mobile IP external agent (FA) function of the packet data service node (PDSN), a call to the Dormant function, the base station controller (BSC) for the packet data service It handles existing packet control functions (PCFs) such as temporary storage of user packets, PPP packet splitting / combining functions, external agents of mobile IP, IP in IP processing, IP encryption, IP address assignment, and route. It provides functions of the existing packet data service node (PDSN), such as assignment and mobile IP message processing, remote authentication dial-up user service (RADIUS) or DIAMETER client function. However, the existing RP connection signal processing is not performed.

Looking at the process of forwarding and processing the packet, the packets received from the base station controller (BSC) are made into a complete end-to-end protocol (PPP) frame through a combination process if necessary, and the IP packet of the mobile station (MS) after PPP processing. Is transmitted to the IP network according to the general routing method. The packet received from the IP network is made into a PPP frame, and then divided and transmitted according to the size of a radio link protocol of the wireless network.

Here, IP packets transmitted to the IP network are delivered to the next node along a path determined by a routing protocol.

4 is a flowchart illustrating a control management method for integrating network elements according to the present invention, in which a packet data service node (PDSN) function is provided to a packet control function (PCF) to provide an efficient network structure and data service function. A control management procedure in an external agent (FA) controller (FAC) that governs a plurality of packet control functions (PCFs) to collectively accommodate the same network elements.

Referring to the overall control management procedure, first, the base station controller interworking signal processing unit 301 of the packet control function PCF performs a call processing function for establishing a data path with the base station controller BSC. Subsequently, when a data path with the base station controller BSC is established, a link layer is established with the mobile station MS. After the connection layer setup is completed, the packet control function (PCF) relays the message to the FA controller (FAC) upon receiving the mobile IP message from the mobile station (MS), and the FA controller (FAC) After the authentication is checked in the database (DB), if authentication is completed, a mobile IP registration request (MIP-RRQ) message is transmitted to the mobile IP home agent (HA). If authentication is the first time, the authentication process is started.

Now, the control management procedure for network element integration according to the present invention will be described in more detail.

First, after completion of the logical connection between the base station controller BSC and the packet control function PCF, the mobile station MS sends a PPP link establishment request to the packet control function PCF. The packet control function (PCF) receiving this is processed by the end-to-end protocol processing unit 306 and completes the end-to-end connection (PPP Link) setup with the mobile terminal (MS).

After that, the mobile station MS transmits the mobile IP registration request message to the packet control function PCF for mobile IP registration, and the packet control function PCF receives the mobile IP external agent function processing unit. Transmit to the FA controller (FAC) through the (303).

As shown in FIG. 4, when a mobile IP registration request message is received from a packet control function (PCF) (401), the FA controller (FAC) determines network access identifier (NAI), which is subscriber identification information, in the received mobile IP registration request message. After extracting (402), to determine whether the authentication is completed by searching the database based on this (403).

As a result of the verification, if the authentication is already confirmed, the authentication procedure is omitted and a mobile IP registration request message is immediately generated and transmitted to the mobile IP home agent 209 (406).

As a result of authentication, when authentication is attempted for the first time, subscriber authentication is handled using AAA server and RADIUS or DIAMETER protocol. That is, an authentication message is generated and transmitted to the AAA server (404), and upon receipt of an authentication completion (ACK) message from the AAA server, the authentication is updated in the database DB (405). In operation 406, the mobile IP home agent 209 generates a mobile IP registration request message to be transmitted to the mobile IP home agent 209.

Thereafter, when the mobile IP registration response message is received from the mobile IP home agent 209 (407), it is transmitted to the mobile terminal (MS) (408).

Here, the reason for omitting the authentication procedure when the subscriber authentication is completed in the DB search results, since the FA controller is responsible for a plurality of packet control functions (PCF), so the authentication is completed from the AAA server when performing the primary location registration in PCF A, This is because omitting the authentication procedure when performing secondary location registration in PCF B enables fast handoff processing and reduces the load on the AAA server.

The method of the present invention as described above may be implemented as a program and stored in a computer-readable recording medium (CD-ROM, RAM, ROM, floppy disk, hard disk, magneto-optical disk, etc.).

The present invention described above is capable of various substitutions, modifications, and changes without departing from the spirit of the present invention for those skilled in the art to which the present invention pertains, and the above-described embodiments and accompanying It is not limited to the drawing.

The present invention as described above has the following effects as compared to the configuration in which the existing PCF and PDSN are separated.

First, since the RP connection between the PCF and the PDSN disappears, virtual link setup is unnecessary and the GRE protocol is not required.

Second, the GRE / PPP overhead on the RP connection is eliminated, which reduces the traffic load on the network and reduces the data transmission delay by integrating two network elements into one.

Third, it is easy to accept IPv6 in the future, and in the conventional case, all packets are delivered through PDSN unconditionally, so both PCF and PDSN have a burden of packet processing, but in the present invention, only one system processes and routes packets to itself. (Routing) can be distributed, resulting in a dispersion effect in data transmission.

Fourth, it is also in line with the technical trend to lower the 3GPP2 FA function to RAN.

Claims (7)

In the control management method for the integration of network elements in the next generation mobile communication network-based integrated Internet protocol (ALL-IP) network, A packet control function (hereinafter referred to as "PCF") for interworking a radio access network (RAN) to a packet network, and a function as a connection node for connecting a data subscriber connected through the radio access network (RAN) to the packet network. Integrate the packet data service node (hereinafter referred to as "PDSN") function to perform as a mobile Internet protocol (hereinafter referred to as "mobile IP") service, the mobile IP external agent (FA) of the PDSN to the PCF when providing a service A first step of integrating the function and the link layer termination function of the mobile terminal; When requesting mobile IP registration from the mobile terminal, an external agent controller (hereinafter referred to as " FAC ") that manages a plurality of PCFs extracts subscriber identification information from the mobile IP registration request message received through the PCF in a database. A second step of searching for an existing authentication; A third step of transmitting a mobile IP registration request message directly to a home agent (HA) without performing authentication again in accordance with the search result of the second step; And A fourth step of notifying the mobile terminal of the received mobile IP registration response message when receiving a mobile IP registration response message from the home agent HA; Control management method for network element integration in a communication system comprising a. The method of claim 1, As a result of the search in the second step, an authentication message is transmitted to the authentication server at the time of initial authentication, and upon completion of authentication from the authentication server, the authentication completion fact is updated in the database, and then the home agent HA is moved to the IP registration request. A fifth step of sending a message; And A sixth step of notifying the mobile terminal of the received mobile IP registration response message when receiving a mobile IP registration response message from the home agent HA; Control management method for network element integration in the communication system further comprising. The method according to claim 1 or 2, The packet control function (PCF), User Datagram Protocol (UDP) processing unit, Internet Protocol (IP) processing unit, Internet Protocol Encryption (IPsec) unit, end-to-end protocol (PPP) processing unit, connection layer, physical layer, A base station controller interworking signal processor configured to process various signals related to data call-related call processing and resource management received from the base station controller (BSC); The mobile terminal (MS) performs the authentication for the Internet protocol (IP) network access through the authorization / authentication / billing protocol and transfers the billing information generated in the system to the authorization / authentication / billing (AAA) security manager Performing authorization / authentication / billing (AAA) protocol client processing; Mobile Internet Protocol (IP) external agent function processing unit for processing the mobile terminal (MS) and Mobile Internet Protocol (IP) -related messages and manages visitor details Control management method for network element integration in a communication system comprising a. The method of claim 3, wherein The packet control function (PCF), It handles existing packet control functions (PCF) such as Dormant function for packet data service, call setup function with the base station controller (BSC), temporary storage function of user packet, and splits / combines end-to-end (PPP) packets Function, external agent function of Mobile Internet Protocol (IP), Internet Protocol (IP in IP) processing function, Internet Protocol (IP) encryption function, Internet Protocol (IP) address assignment function, routing and mobile Internet protocol ( IP) provides the functionality of an existing packet data service node (PDSN), such as message processing, remote authentication dial-up user service (RADIUS), or DIAMETER client function, but does not exist between the radio access network (RAN) and the packet network. Control management method for network element integration in a communication system, characterized in that the signal processing by the connection method (RP connection method) is not performed . The method of claim 4, wherein The packet forwarding process in the packet control function (PCF), If necessary, packets received from the base station controller (BSC) are combined into a complete end-to-end protocol (PPP) frame through a combination process, and end-to-end protocol (PPP) processing is performed. Then, the Internet protocol (IP) of the MS is performed. The packet is forwarded to the Internet Protocol (IP) network according to a general routing method, and the packet received from the Internet Protocol (IP) network is made into an end-to-end protocol (PPP) frame, followed by a radio link protocol of a wireless network. Control management method for network element integration in a communication system, characterized in that for transmitting according to the size of. In a communication system having a processor for control management for network element integration in an integrated internet protocol (ALL-IP) network, A packet control function (hereinafter referred to as "PCF") for interworking a radio access network (RAN) to a packet network, and a function as a connection node for connecting a data subscriber connected through the radio access network (RAN) to the packet network. Integrate the packet data service node (hereinafter referred to as "PDSN") function to perform as a mobile Internet protocol (hereinafter referred to as "mobile IP") service, the mobile IP external agent (FA) of the PDSN to the PCF when providing a service A first function for integrating a function with a link layer termination function of a mobile terminal; When requesting mobile IP registration from the mobile terminal, an external agent controller (hereinafter referred to as " FAC ") that manages a plurality of PCFs extracts subscriber identification information from the mobile IP registration request message received through the PCF in a database. A second function of searching for an existing authentication; A third function of transmitting a mobile IP registration request message directly to a home agent (HA) without performing authentication upon pre-authentication according to the search result of the second function; And A fourth function of notifying the mobile terminal of the received mobile IP registration response message when receiving a mobile IP registration response message from the home agent HA; A computer-readable recording medium having recorded thereon a program for realizing this. The method of claim 6, According to the search result of the second function, the authentication message is sent to the authentication server at the time of initial authentication, and when the authentication completion from the authentication server is updated in the database, the mobile agent moves to the home agent HA. A fifth function of sending a registration request message; And A sixth function of notifying the mobile terminal of the received mobile IP registration response message when receiving a mobile IP registration response message from the home agent HA; A computer-readable recording medium that records a program for further realization.