KR100418858B1 - Method and Apparatus for Providing Real-Time Internet Communication Using User Account with Domain Name - Google Patents

Abstract

The present invention relates to a method and apparatus for real-time internet communication using a user account as a domain. Particularly, the present invention provides a method for performing a client authentication procedure and requesting whether to use a dynamic domain name service to a connection server through a mapping server. Wow; Transmitting a user account and current IP address to the dynamic domain name server when applying for the dynamic domain name service; And setting a static domain name based on the user account. Therefore, according to the present invention, by assigning a fixed domain corresponding to a user account input regardless of an IP address changed in real time and owning a site, a multifunctional web community and a messenger function can be implemented. .

Description

Method and Apparatus for Providing Real-Time Internet Communication Using User Account with Domain Name}

The present invention relates to a real-time Internet communication method and apparatus using a user account as a domain, and more particularly, to a dynamic domain name server for updating Internet protocol (hereinafter, referred to as 'IP') information in real time. Server (hereinafter, referred to as 'DDNS') to assign a fixed domain corresponding to a user account to a client (hereinafter, referred to as a 'first client') that desires to assign a fixed domain. The client relates to a real-time Internet communication method and apparatus using a user account as a domain for creating a web community that can communicate with or exchange data in real time with a person who accesses its site.

Recently, due to the generalization of the Internet, the Internet can be easily used in the home, and communication and information exchange with other computers are possible through the Internet. In order to communicate with other computers connected to the Internet, we need to know the address of a computer connected to the Internet, just as we need to know the phone number of the other person connected to the telephone network. A computer's address is represented by a numeric address (e.g., 123.234.56.7), but because it is difficult to understand or remember, the address is represented by an alphabetic domain address system (e.g. nic.or.kr). Is developed and used as the homepage address. Thus, public IP addresses or domain addresses exist with unique, non-duplicate names throughout the world, so that any computer around the world can communicate if it is connected to the Internet.

1 is a conceptual diagram of a general domain name service, in which a user communicates with a counterpart computer by a domain name when a user wants to search a website (eg, www.nic.or.kr) using his or her computer. .

When the user (1) enters the www.nic.or.kr address in the address bar of the web browser, the web browser first displays the IP address of www.nic.or.kr in the Domain Name Server (DNS). Query what is DNS (2) retrieves the IP address of the inquired www.nic.or.kr in its database and transmits the IP address (for example, 123.234.56.7) corresponding to the inquired domain address to the web browser. The DNS 2 itself has a database used for resolving an IP made to search and recognize a computer on the Internet into a domain name made easy for the user 1 to remember. Therefore, in order to provide various domain name services to the user 1, it is desirable to secure a large number of various domain names and store them in a database. The web browser receiving the response to the query communicates with the web server 3 using the IP address. Here, communication between each other (e.g., user 1 and DNS 2, user 1 and web server 3, DNS 2 and web server 3) is via the Internet 4 .

As such, the translation of an English address (ie, a domain name) into a numeric address (ie, an IP address) is called a domain name service, and the software that performs this role is called a domain name system. To make your domain name available to other users on the Internet, you must register your domain name with your domain name server (system). Domains that are not registered in DNS cannot be used because they cannot be translated into IP addresses by other users.

There are two ways to assign an IP address: static (static) IP address allocation method and dynamic IP address assignment method. Static IP address assignment method is a method for allocating a user when the client wants to connect to the Internet. Is a way to assign users if they work behind a firewall or are not connected to the Internet. Therefore, you must use a static IP address when connecting to the Internet, but you do not need to use a static IP address when you are not connected to the Internet, and you can use it within the range of dynamic IP addresses. The IP address system was established by ICANN (Internet Corporation for Assigned Names and Numbers), which manages IPs around the world, while domestic IP addresses are entrusted and managed by the Korea Internet Information Center (KRNIC). If an Internet user needs an IP address, it can be assigned and used by an ISP (Internet Service Provider) or a higher Internet Registry (IR). Therefore, since the IP address is not owned by the address but is only authorized to use the address, the IP address must be returned to the assigned location according to the prescribed procedure when the IP address is not used.

For users who want to connect to the Internet through an ISP with a single PC, ISPs use a dynamic IP address assignment method. As part of the connection process, the point-to-point protocol (PPP) service that is connecting tells the PC which PPP interface to use during the current connection cycle. This dynamic IP address will be different each time you connect to your ISP. The use of such dynamic IP addresses saves a limited static IP address space and allows the use of a spare address space, which provides flexibility in the design of the network, which makes it easy to manage address assignment. Because of this advantage, most ISPs use a method of assigning dynamic IP addresses.

However, such a general domain name service has various problems. First, because most homes use the Internet using Internet equipment, such as Asymmetric Digital Subscriber Line (ADSL) or cable modems, other Internet services may be available, but they may be available to other users. Internet archives, etc.). Second, when the information of the Internet service is to be changed, it is inconvenient to upload the changed data by accessing the server providing the Internet service, and the data cannot be guaranteed because the data is located in another server. Third, it takes a lot of time to change the domain name. In the conventional domain name service, the actual utilization rate was very low because the user changed the IP only after performing the IP change procedure using the web, and it was inconvenient to wait 24 to 48 hours for the changed IP address to be renewed. there was. Fourth, even those who own their own homepages could not know what visitors are currently accessing their homepages.

Accordingly, the present invention has been made to solve the above-mentioned conventional problems, and a first object of the present invention is to assign a fixed domain in real time to an Internet user by using a dynamic domain name server. The present invention provides a real-time Internet communication method and apparatus using a user account as a domain that can provide Internet services to a client (hereinafter referred to as a "second client") who wants to access a site.

A second object of the present invention is to provide a method and apparatus for real-time internet communication using a user account, which can establish a messenger function with a web community and communicate with or exchange data with a second client visiting a site in real time. There is.

The third object of the present invention is to use a user account that can communicate with a desired second client as a domain by adding a function of real-time checking of a list of second clients connected to its site when building a web community. The present invention provides a method and apparatus for real-time internet communication.

1 is a conceptual diagram of a general domain name service,

2 is a block diagram of a messenger server group according to the present invention;

3 is a block diagram of a real-time Internet communication device for granting a fixed domain at the request of an Internet user according to the present invention,

4 is a flowchart illustrating a process for granting a fixed domain at the request of an Internet user according to the present invention;

5 is a block diagram of a real-time Internet communication device for creating a web community according to the present invention,

6 is a flowchart illustrating a process for creating a web community according to the present invention;

FIG. 6A is an exemplary diagram illustrating a use state of clients accessing a corresponding domain. FIG.

7 is a block diagram of a real-time Internet communication device for performing a messenger function according to the present invention,

8 is a flowchart illustrating a process for performing a messenger function according to the present invention.

♣ Explanation of symbols for the main parts of the drawing ♣

10: mapping server group 20: access server

30: other server group 32: web server

34: Memo Server 36: Pass Server

38: Statistics Server 40: Client

50: dynamic domain name server 60: applet

In order to achieve the above object, the present invention provides a real-time Internet communication device using a user account that provides a domain name corresponding to an IP address assigned by a client as a domain, and is responsible for communicating with the client, and real-time messages and files. A first server that performs basic functions such as transmission, chat, 1: 1 conversation, and connection confirmation, and relays data transmission between the client and other servers when necessary (hereinafter, the trademark of 'Applicant' A mapping server group consisting of a group of mapping servers'; It is interconnected with the mapping server group, and stores member's personal information for each member, including a database, and stores member information for each content to perform a messenger function, performs an authentication procedure of a client, and any of the client and the mapping server group. An access server connecting a server of the server and relaying a connection between the client and other external servers; And other server groups that are interconnected to the mapping server group and the access server, and that perform a web community function, a messenger function, a message storage function to a non-access user, and a data transmission function to the client.

In addition, the present invention is a real-time Internet communication method using a user account that provides a domain name corresponding to the IP address assigned by the client as a domain, performing the authentication process of the client, and the dynamic domain to the access server through the mapping server Requesting whether to use the name service; Transmitting a user account and current IP address to the dynamic domain name server when applying for the dynamic domain name service; And setting a static domain name based on the user account.

The present invention provides an Internet tool for assigning a fixed domain for a dynamic IP address to provide a static domain corresponding to a user account to a user (ie, a first client) using the Internet, and the first client can build an Internet site. By providing a web community and a messenger function for communicating in real time with the visitor to his site can be implemented. For this purpose, it is desirable to appropriately control the interworking between the mapping server, the DDNS, the web community server, and the messenger server. Here, the site is a concept of an Internet server that uses a user account assigned as a domain address after accessing the real-time domain name service of the present invention, and downloads a dedicated program provided by the real-time domain name service of the present invention to operate the site. Can be. Clients with user accounts become server administrators on the Internet.

Hereinafter, a preferred embodiment of a real-time Internet communication method and apparatus using a user account according to the present invention as a domain will be described in detail with reference to the accompanying drawings.

2 is a block diagram of a messenger server group according to the present invention, wherein the messenger server group includes a mapping server group 10, an access server 20, a database 25, and other server groups 30. The other server group 30 again includes a web server 32, a memo server 34, a pass server 36, and a statistics server 38.

The mapping server group 10 is connected to the client and is in charge of communication with the client, and performs a messenger function for providing basic services such as real-time message and file transfer, chat, 1: 1 conversation, and connection check, If necessary, it consists of a group of mapping servers 10a, 10b, ..., 10e which relay data transmission between the client and another server. The communication with the client is performed through the Internet, and in addition to the basic messenger function described above, a memo (note) function for sending a memo to all the specified people and members, an absence setting function for leaving a message in the absence, and an external user registration function are added. Can be set to An e-mail can send a message to anyone who knows the other party's address, but a messenger can communicate only with members who subscribe to the same service. However, while it takes at least one to two minutes to transmit data using e-mail, the messenger has an advantage that it can be immediately sent to the other party. In order to use the messenger function, the client must download a dedicated program provided by the service provider and install it on his computer. Internet users who have installed a dedicated messenger program automatically save their messenger ID and password so that they can access the messenger automatically every time they boot up their computer.

The access server 20 is interconnected with the mapping server group 10, performs an authentication procedure (eg, whether ID and password match) of the first client, connects the first client with an arbitrary mapping server, Relay connections with the database 25 and other external servers. The authentication process of the first client is performed based on the member information stored in the database 25, and the database 25 includes personal information about the member and various contents for performing a messenger function (eg, group of colleagues, net friends). Member information for each meeting, club meeting, etc.) may be stored. In addition, when the first client connects, the access server 20 determines the mapping server with the least user among the mapping servers, and induces the first client to access the mapping server.

The other server group 30 is interconnected with the mapping server group 10 and the access server 20, and includes a web server 32, a memo server 34, a pass server 36, and a statistics server 38. do. The web server 32 is connected to the mapping server group 10, the server name is registered in the domain name server, and is a server hardware that can be searched for information in the form of Uniform Resource Locator (URL) by the general Internet users. The web server 30 handles Internet users' requests by server programs such as NCSA, CERN, Apache, JIGSAW, which is a server for Unix, IIS, which is a server for Windows NT, and WebSite, which is a Windows 95/98 server. . In particular, the web server 30 performs a function of constructing a web community for implementing communication between clients. The web community provides various categories that meet the purpose and desires of the members, and ensures maximum autonomy of the members through functions such as club activities, club alliance, and small group composition. It is desirable to construct them easily and efficiently. To realize this, the web community includes various contents such as chats, announcements, bulletin boards, archives, voting, e-mails, and small group management so that the web community can immediately respond to members' needs. In addition to these contents, collecting and actively reflecting the contents required by members is one way to build an efficient web community.

The memo server 34 is connected to the mapping server group 10 and transmits a message to a member who is not connected to the homepage and manages a buddy for each member. The buddy management function is a convenient function that shows the status of the other party (eg, whether it is connected to the Internet or its own site) when the member or member group is registered on the site by inputting an address book or an IP address. Therefore, when a client wants to send a message to another client, the buddy management function can be used to determine the connection status of the client. The client can use various methods (eg, message, 1: 1 conversation, e-mail, etc.) according to the client status. You can pass a message. The pass server 36 is connected to the mapping server group 10 and performs a function of relaying 1: 1 data transmission such as file transfer and chat between clients. In order to realize this, interworking with other servers may be preceded if necessary. The statistics server 38 is connected to the web server 32 and performs a function of providing a service for providing statistics on a homepage user access for each month / day / time. By using these statistical services, the number of visitors and time zones of the homepage can be identified, which can be used as a reference for adding and deleting homepage functions. In addition, you can build your own database to store statistical data derived from statistical services, and statistical data can be used to compare and evaluate old and current data at any time. Each of the servers shown in FIG. 2 (that is, the memo server 34, the pass server 36, and the statistics server 38) is shown as a separate device, but this is to explain the roles for each server separately. Since it is shown in figure, it can also be included in the web server 32, and it can also be designed as one server.

3 is a configuration diagram of a real-time Internet communication device for assigning a fixed domain at the request of an Internet user. The real-time Internet communication device includes a mapping server group 10, an access server 20, a database 25, and the like. The server 100 includes a messenger server group 100, a client 40, and a dynamic domain name server (DDNS) 50. Of the components of FIG. 3, the same components as those of FIG. 2 have the same reference numerals, and the description of the same components will be omitted here and the description of FIG. 2 is used.

The client 40 refers to a person who visits the real-time Internet communication device of the present invention. After accessing the access server 20, the client 40 may register as a member or change member information, and use all contents provided by the real-time Internet communication device. Can be. In addition, when using the messenger function, a dedicated program provided by the mapping server may be downloaded and used.

The DDNS 50 is interconnected with the access server 20 and performs a function of allocating a fixed domain name based on the ID of the client 40 authorized by the access server 20 and the current IP. The DDNS 50 should be connected to the Internet using a dedicated line 24 hours a day, and the like is to build a server (e.g., a server that can upload data for each client site) even if it is operated 24 hours a day. More important. Dynamic IP addresses are reserved for the efficient use of fixed IP addresses by ICANN, which manages the entire IP address in advance, for private networks.

One A class: 10.0.0.0-10.255.255.255 (/ 8 prefix)

16 class B: 172.16.0.0-172.31.255.255 (/ 12 prefix)

256 C class: 192.168.0.0-192.168.255.255 (/ 16 prefix)

These IP address assignments and assignments must be registered in a publicly accessible registry and assigned in a hierarchical fashion according to the Network Infrastructure Topology. Therefore, when the client 40 connects to any one of the mapping server groups 10 and authenticates to use its dynamic IP, the DDNS 50 sets the domain based on the user account and the current IP. .

4 is a flowchart illustrating a process for assigning a fixed domain at the request of an Internet user, and assumes that a first client has downloaded a dedicated program for performing a messenger function from a mapping server.

First, the first client operates a dedicated program provided by the real-time Internet communication device of the present invention (S410) to access the access server, and performs an authentication procedure. The access server compares the contents input by the first client with the contents stored in the database to determine whether to authenticate. Next, the first client accesses the mapping server through the access server (S420). The access server stores the IP address currently used by the first client in the process of performing an authentication procedure, determines the server with the least user among the mapping servers, and induces the first client to access the mapping server. The first client accesses any one of the mapping servers derived from the access server, and transmits whether to use the domain name service to the access server through the corresponding mapping server (S430). Here, a message about whether to use the domain name service is transmitted from the first client to the mapping server, and again from the mapping server to the access server.

The access server determines whether the first client has applied for the domain name service on the basis of the message transmitted from the mapping server (S440), and when applying for the domain name service, the user account of the first client and the currently used IP address through DDNS. Transmit (S450). Thereafter, the DDNS sets a domain corresponding to the ID input by the client based on the user account and the IP address transmitted from the access server (S460). When a client's domain is set in DDNS, the domain is unique, so the client can have the same effect as owning its own site. Therefore, the client can use all the contents provided by the real-time Internet communication device of the present invention, and can set a desired environment for performing his own messenger function and web community function. After the client performs the desired other functions (S470), all processing is terminated.

5 is a block diagram of a real-time Internet communication device for generating a web community according to the present invention, the real-time Internet communication device is a client 40, mapping server group 10, access server 20, database 25 And a messenger server group 100 and an applet 60 formed of other server groups 30. Of the components of FIG. 5, the same components as those of FIG. 2 or 3 are denoted by the same reference numerals, and the description of the same components will be omitted here and the description of FIG. 2 or 3 is used.

The applet 60 is connected to the statistics server 38 of the other server family 30, and the applet 60 is derived from an application that represents an application and is a small and independent part included in a web page. Say an application. The applet 60 can be used only if Java processing function is provided in the web browser. Unlike the static program mainly for text or two-dimensional picture developed in HTML (hypertext display language), the applet 60 can use dynamic information such as three-dimensional cartoon movie. It is a ready-to-run application that can be developed in the Java language. Java applets have the advantage of being able to use sound, call a document on a URL to a browser, and communicate between applets within the same HTML document. By using the applet 60, the client 40 may check the use status of the second client visiting his homepage in real time.

6 is a flowchart illustrating a process for creating a web community according to the present invention.

First, the first client operates a dedicated program provided by the real-time Internet communication device of the present invention (S605) to connect to the access server, and performs an authentication procedure. The access server compares the contents input by the first client with the contents stored in the database to determine whether to authenticate. Next, the first client accesses the mapping server through the access server (S610). The access server stores the IP address currently used by the first client in the process of performing an authentication procedure, determines the server with the least user among the mapping servers, and induces the first client to access the mapping server. The first client accesses any one of the mapping servers derived from the access server, and transmits the domain of the web site viewed through the mapping server to the mapping server currently connected (S615). If the current mapping server is not connected to the web server, after accessing the web server through the access server, the mapping server retransmits the domain transmitted from the first client to the web server (S620). The web server grasps the domain transmitted from the mapping server and the site use status of the domain and transmits it to the statistics server (S625). Accordingly, the statistics server may identify the second client accessing the domain based on the information transmitted from the web server (the domain accessed by the first client and the usage status of the site). In addition, by transmitting the information to the applet in real time, the first client can confirm the information.

Next, the web server determines whether the second client is currently using a site corresponding to the domain transmitted by the first client (S630), and if there is a second client, the web server lists the second client using the domain. Extract it and transmit it to the mapping server (S635). In addition, the mapping server registers the list and transmits the list to the client requesting the list (S640) so that the client can check other clients accessing the site visited by the client. An example list showing the usage status of other clients connected to the domain is shown in FIG. 6A. If the web server determines whether the second client visiting the domain has moved to another domain (S645) and moves to another domain, the web server proceeds to step S615 and repeats the subsequent steps, even in the domain where the second client has moved. Provides services to identify other clients. Next, if there is no other client in the domain visited by the second client in step S630 or the second client does not move to another domain in step S645, the client performs other functions selected by the client (S650). Terminate the process.

7 is a block diagram of a real-time Internet communication device for performing a messenger function according to the present invention, the real-time Internet communication device is a mapping server group 10, access server 20, database 25, other server group ( 30 includes a messenger server group 100 and a client 40. The same components as in FIG. 2 among the components of FIG. 7 have the same reference numerals, and the description of the same components will be omitted here and the description of FIG. 2 is used. 7 differs from FIG. 2 in that only the memo server 34 and the pass server 36 are used in the other server group 30.

8 is a flowchart illustrating a process for performing a messenger function according to the present invention, and it is assumed that a first client downloads a dedicated program for performing a messenger function from a real-time internet communication device of the present invention and installs it on his computer. do.

First, the first client operates a dedicated program provided by the real-time Internet communication apparatus of the present invention (S805) to access the access server, and performs an authentication procedure. The access server compares the input contents with the contents stored in the database to determine whether the first client is authenticated. Next, the first client accesses the mapping server through the access server (S810). In the process of performing the authentication procedure, the access server stores the IP address currently used by the first client, determines the server with the least user among the mapping servers, and induces the first client to access the mapping server. 1 After connecting to the mapping server derived from the access server, the client performs a messenger function and inputs information (eg, a message, a data file, etc.) to be transmitted and a list of clients to communicate with (S815). The mapping server determines whether the client has requested a query regarding the list of clients to communicate with (S820), and if the query is requested, the mapping server sends the current state of the second client of the other mapping server to which the client to communicate with is connected to the access server. Inquire (S825). Since the access server knows whether the client is connected every time the clients access the real-time Internet communication device of the present invention, it can know which client is connecting to which mapping server group or other server group.

The access server analyzes the list of clients inquired by the mapping server to determine whether there is a second client currently connected to the real-time Internet communication device of the present invention (S830). The current state of the client is transmitted to the client (S835). After requesting the service, the client selects the client and performs a desired function (eg, chatting, sending a message, sending a file, etc.) by performing a messenger function through the mapping server. If the work requested by the client is through another mapping server, information may be exchanged through interworking with each other.

As a result of the determination in step S830, if there is no second client currently connected, information is transmitted through the memo server (S845). The memo server performs a task of leaving a message to a second client to which the first client is not connected or storing a list of second clients who have a friend. The mapping server determines whether the corresponding second client has set security (S850), and if the security is set, transmits information through the pass server (S855). That is, if a task that can be performed by the user-to-user connection, such as file transfer, is not possible by a security device such as a firewall, the desired task may be performed through the pass server. In step S820, the first client does not request a query or security is not set in step S850, or after the steps S840 and S855, other functions selected by the first client are performed in step S860. After that, all processing ends.

The above description is only for explaining one embodiment, and the present invention is not limited to the above-described embodiment and can be variously changed within the scope of the appended claims. For example, the shape and structure of each component specifically shown in the embodiment of the present invention may be modified.

As described above, according to the real-time Internet communication method and apparatus using the user account according to the present invention, the site is assigned a fixed domain corresponding to the user account input irrespective of the IP address changing in real time By owning it, it is possible to implement a multifunctional web community and messenger function.

In addition, it is possible to form a web community with the desired visitors because the user can know the list of visitors who access their site in real time using the web community function.

Claims (9)

In a real-time Internet communication device that provides a domain name corresponding to the IP address assigned by the client, It is in charge of communication with the client, performs messenger functions that provide basic services such as real-time message and file transmission, chat, 1: 1 conversation, and connection confirmation, and relays data transmission between the client and other servers when necessary. A mapping server group consisting of a group of mapping servers; It is interconnected with the mapping server group, and stores personal identification information for each member and a member information for performing a messenger function, including a database, performs an authentication procedure of the client, and the client and the mapping server. An access server connecting any server in the group and relaying a connection between the client and other external servers; Another server group interconnected with the mapping server group and the access server and configured to perform a web community function, a messenger function, a message storage function to a non-access user, and a data transmission function to the client; And And a dynamic domain name server interconnected with the access server and assigning a fixed domain name based on the ID of the client authorized by the access server and the currently used IP. Real time internet communication device. delete The method of claim 1, An applet connected to the other server group, calling a document on a URL on a web browser, exchanging information in the same HTML document, and sending a usage status to another client visiting the client's homepage; A real time Internet communication device using a user account as a domain, characterized in that further comprising. The method of claim 1, wherein the other server group A web server connected to the mapping server group and configured to process a request of the client by a server program and to configure a web community for implementing communication between the clients; A memo server connected to the mapping server group and transmitting a message to a client not connected to the homepage of the client and managing a buddy for each client; A pass server connected to the mapping server group and relaying 1: 1 data transfer such as file transfer and chat between clients; And Real-time Internet using a user account as a domain connected to the web server, characterized in that it comprises a statistics server for calculating the statistical results for the homepage user access of the client for each month / day / time to provide to the client Communication device. In the real-time Internet communication method for providing a domain name corresponding to the IP address assigned by the client, Performing the authentication procedure of the client and requesting the use of the dynamic domain name service from the mapping server to the access server; Transmitting a user account and an currently used IP address to a dynamic domain name server when the dynamic domain name service is applied; And Setting a static domain name based on the user account, The access server determines the server with the least number of clients among the mapping server group to induce the client to access the mapping server, the client is connected to the corresponding mapping server derived from the access server Real-time Internet communication method using account as domain. delete The method of claim 5, Requesting, by the client, a list of clients accessing the site by transmitting the domain of the currently connected site to the web server through the mapping server; The web server transmitting the usage status of the domain and the site transmitted from the client to a statistics server; And If there is a client using the domain transmitted to the client, the web server further comprises the step of creating the client list and notifying the client requesting the client list to the real time using the user account as the domain. Internet communication method. The method of claim 5, The client performing a messenger function to input information to be transmitted and the client list to be communicated with; Retrieving a connection state of other clients through the access server when the client requests a query for the input client list; If a client currently accessing a site of the client requesting the list of clients is in the client list, the access server sending the current state of the client to the client requesting the client list; And The client further comprises the step of communicating with the client by performing the messenger function, real-time Internet communication method using a user account as a domain. The method of claim 8, If the other client that is currently connected to the client's site that requested the list of clients is not in the client list, sending information through a memo server; If the other client has set security, transmitting the information through a pass server, wherein the real time Internet communication method using a user account as a domain.