A multi-link load balancing method and system

Abstract

The present invention relates to the field of communication technology, and more specifically, to a multi-link load balancing method and system, the method comprising obtaining user access traffic information and a pre-set static load balancing algorithm; classifying the traffic into a model to obtain the classified traffic information; determining whether the link accessed by the traffic meets the required model for the classified traffic information to obtain link information that meets the traffic access requirements; load balancing the traffic to the healthy server or client to obtain the access result information of the server or client. It can be understood that the present invention achieves high availability, high security and scalability of the server by using local load balancing and application optimization equipment, realizes reasonable distribution of data flows, and makes full use of all data centers, links and servers.

Description

Technical Field

[0001] The present invention relates to the field of communication technology, and in particular to a multi-link load balancing method and system. Background Art

[0002] With the changes in the globalization of enterprises, the demand for high availability of applications that can be accessed anytime and anywhere is gradually increasing. For online banking of banks, users are gradually distributed all over the world. With the switching of time zones, users may use it at any time within 24 hours. For a large international enterprise, the rest time of one area is exactly the working time of other areas. Under the global working mode, the production efficiency of enterprises has also been greatly improved. At the same time, the demand for high availability of enterprise application systems has also been raised to a very high level. Under the high availability demand of enterprise application systems, the access speed of users is greatly affected due to problems such as packet loss and delay caused by interconnection. Summary of the invention

[0003] The purpose of the present invention is to provide a multi-link load balancing method and system to improve the above problems. In order to achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0004] On the one hand, the present application provides a multi-link load balancing method, the method comprising:

[0005] Acquire first information, where the first information is user access traffic information and a preset static load balancing algorithm;

[0006] Sending the first information to a first model for processing to obtain second information, wherein the first model is a model for classifying the traffic, and the second information is the classified traffic information;

[0007] Sending the second information to a second model for processing to obtain third information, wherein the second model is a model for determining whether a link accessed by the classified traffic information meets the requirements, and the third information is link information that meets the traffic access requirements;

[0008] The first information and the third information are sent to the third model to obtain fourth information, wherein the fourth model is a model for balancing the traffic load to the healthy server or client, and the fourth information is access result information to the server or client.

[0009] Optionally, sending the first information to a first model for processing to obtain second information includes:

[0010] Classify the access flow information of the users in the first information to obtain the access flow information of the intranet user terminal and the access flow information of the extranet user terminal;

[0011] Domain name resolution is performed on the access flow information of the intranet user terminal and the access flow information of the extranet user terminal respectively to obtain domain name information of at least one classified flow.

[0012] Optionally, sending the second information to a second model for processing to obtain third information includes:

[0013] Obtaining an access cache record of the domain name information of the classified traffic in the local cache;

[0014] The health status of the link where the traffic is located is determined according to whether the link in the access cache record is accessible, and the healthy link where the classified traffic is located is processed using a preset static load balancing algorithm to obtain the time interval information of the third model sending a query request in reverse to the LDNS to receive a response and the IP address of the domain name within a certain period of time;

[0015] Obtaining a first threshold value, which is a threshold value of time interval information for the third model to send a query request in reverse to the LDNS and receive a response;

[0016] The first threshold and the time interval information are compared, and link information with a time interval information greater than the first threshold is marked as link information that meets the requirement.

[0017] Optionally, sending the first information and the third information to a third model to obtain fourth information includes:

[0018] Calling the flow rate of the access flow information of the intranet user terminal in the second information and the flow rate of the access flow information of the extranet user terminal;

[0019] Initiate a connection request to the IP address of the domain name, and obtain access result information of the client by load balancing the access traffic information of the external network user terminal to the client;

[0020] Allocating the traffic of the access traffic information of the intranet user terminal to the link information reaching the requirement respectively;

[0021] After converting the IP address of the domain name into the public network address of the corresponding ISP network segment, the traffic is sent to the internal server to obtain the access result information of the internal server.

[0022] Optionally, the sending the second information to a second model for processing to obtain third information further includes:

[0023] Marking link information with a time interval information less than or equal to the first threshold as link information that does not meet the requirement;

[0024] The link information that does not meet the requirements is shielded through a firewall, and a first command is sent, wherein the first command is to establish a backup link in a backup load balancing device;

[0025] The access flow information of the link that does not meet the requirements is sent to the backup link for transmission, the access flow information of the link that does not meet the requirements is marked, and a command for maintaining the access flow information link is sent to the communication equipment of the maintenance personnel.

[0026] On the other hand, the present application provides a multi-link load balancing system, the system comprising:

[0027] A first acquisition unit, configured to acquire first information, wherein the first information is user access flow information and a preset static load balancing algorithm;

[0028] a first processing unit, configured to send the first information to a first model for processing to obtain second information, wherein the first model is a model for classifying the traffic, and the second information is the classified traffic information;

[0029] a second processing unit, configured to send the second information to a second model for processing to obtain third information, wherein the second model is a model for determining whether a link accessed by the classified traffic information meets the requirements, and the third information is link information that meets the traffic access requirements;

[0030] The third processing unit is used to send the first information and the third information to the third model to obtain fourth information. The fourth model is a model that balances the traffic load to the healthy server or client, and the fourth information is access result information of the server or client.

[0031] Optionally, the system comprises:

[0032] A first processing subunit is used to classify the access flow information of the users in the first information to obtain the access flow information of the intranet user terminal and the access flow information of the extranet user terminal;

[0033] The second processing sub-unit is used to perform domain name resolution on the access flow information of the intranet user terminal and the access flow information of the extranet user terminal respectively to obtain domain name information of at least one classified flow.

[0034] Optionally, the system comprises:

[0035] A first acquisition subunit is used to obtain an access cache record of the domain name information of the classified traffic in a local cache;

[0036] The third processing subunit is used to determine the health of the link where the traffic is located according to whether the link in the access cache record is accessible, and process the healthy link where the classified traffic is located using a preset static load balancing algorithm to obtain the time interval information of the third model sending a query request in reverse to the LDNS to receive a response and the IP address of the domain name within a certain period of time;

[0037] The second acquisition subunit is used to acquire a first threshold value, which is a threshold value of the time interval information for the third model to send a query request in reverse to the LDNS and receive a response;

[0038] The fourth processing subunit is used to compare the first threshold with the time interval information, and mark the link information with the time interval information greater than the first threshold as the link information that meets the requirement.

[0039] Optionally, the system comprises:

[0040] A fifth processing subunit, configured to call the flow rate of the access flow information of the intranet user terminal in the second information and the flow rate of the access flow information of the extranet user terminal;

[0041] A sixth processing sub-unit, configured to initiate a connection request to the IP address of the domain name, and obtain access result information of the client by load balancing the access flow information of the external network user terminal to the client terminal;

[0042] A seventh processing sub-unit, used for respectively allocating the traffic of the access traffic information of the intranet user terminal to the link information reaching the requirement;

[0043] The first sending subunit is used for converting the IP address of the domain name into a public network address of a corresponding ISP network segment, and then sending the traffic to an internal server to obtain access result information of the internal server.

[0044] Optionally, the system further comprises:

[0045] A fourth processing unit, configured to mark link information having a time interval less than or equal to the first threshold as link information that does not meet the requirement;

[0046] A fifth processing unit, configured to shield the link information that does not meet the requirement through a firewall, and send a first command, wherein the first command is to establish a backup link in a backup load balancing device;

[0047] The first sending unit is used to send the access flow information of the link that does not meet the requirements to the backup link for transmission, mark the access flow information of the link that does not meet the requirements, and send a command to maintain the access flow information link to the communication equipment of the maintenance personnel.

[0048] The beneficial effects of the present invention are:

[0049] It can be understood that the present invention achieves high availability, high security and scalability of the server by using local load balancing and application optimization equipment, realizes the reasonable distribution of data flow, and makes full use of all data centers, links and servers. It not only expands the overall processing capacity of the application system and improves its stability, but also effectively improves the user's access experience and reduces the organization's IT investment cost. In addition, multiple servers are set up to monitor the health status of the servers in real time. If a server fails, it will be cleared from the service queue to ensure that users can access the application normally and ensure the correctness of the response content.

[0050] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or be understood by implementing the embodiments of the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the written description, claims, and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0052] Figure 1 A schematic diagram of a multi-link load balancing method according to an embodiment of the present invention;

[0053] Figure 2 The present invention is a schematic diagram of a multi-link load balancing device according to an embodiment of the present invention. DETAILED DESCRIPTION

[0054] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0055] It should be noted that similar reference numerals and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in the subsequent drawings. At the same time, in the description of the present invention, the terms "first", "second", etc. are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0056] Example 1

[0057] like Figure 1 As shown, this embodiment provides a multi-link load balancing method, which includes step S1, step S2, step S3 and step S4.

[0058] Step S1, obtaining first information, wherein the first information is user access flow information and a preset static load balancing algorithm;

[0059] Step S2: sending the first information to a first model for processing to obtain second information, wherein the first model is a model for classifying the traffic, and the second information is the classified traffic information;

[0060] Step S3, sending the second information to the second model for processing to obtain third information, wherein the second model is a model for determining whether the link accessed by the classified traffic information meets the requirements, and the third information is the link information that meets the traffic access requirements;

[0061] Step S4, sending the first information and the third information to the third model to obtain fourth information, wherein the fourth model is a model for balancing the traffic load to the healthy server or client, and the fourth information is access result information to the server or client.

[0062] It can be understood that the present invention directly classifies the access traffic information and then sends it through a healthy link through traffic load balancing. The healthy link refers to a link without failures and which ensures stable data reception and fast response speed, thereby achieving high availability of the system.

[0063] It can be understood that the present invention achieves high availability, high security and scalability of the server by using local load balancing and application optimization equipment, realizes the reasonable distribution of data flow, and makes full use of all data centers, links and servers. It not only expands the overall processing capacity of the application system and improves its stability, but also effectively improves the user's access experience and reduces the organization's IT investment cost. In addition, multiple servers are set up to monitor the health status of the servers in real time. If a server fails, it will be cleared from the service queue to ensure that users can access the application normally and ensure the correctness of the response content.

[0064] In a specific implementation of the present disclosure, step S21 includes step S21 and step S22.

[0065] Step S21, classifying the access flow information of the users in the first information to obtain the access flow information of the intranet user terminal and the access flow information of the extranet user terminal;

[0066] Step S22: performing domain name resolution on the access flow information of the intranet user terminal and the access flow information of the extranet user terminal respectively to obtain domain name information of at least one classified flow.

[0067] It can be understood that the present invention achieves high availability by parsing different traffic information and then classifying and aggregating them, determining the corresponding link based on the classified and aggregated information, and quickly and efficiently judging whether the link meets the requirements.

[0068] In a specific implementation of the present disclosure, step S3 includes step S31, step S32, step S33 and step S34.

[0069] Step S31, obtaining the access cache record of the domain name information of the classified traffic in the local cache;

[0070] Step S32: judging the health of the link where the traffic is located according to whether the link in the access cache record is accessible, and processing the healthy link where the classified traffic is located using a preset static load balancing algorithm to obtain the time interval information of the third model sending a query request in reverse to the LDNS to receive a response and the IP address of the domain name within a certain period of time;

[0071] Step S33: Obtain a first threshold value, which is a threshold value of the time interval information for the third model to send a query request in reverse to the LDNS and receive a response;

[0072] Step S34: Compare the first threshold with the time interval information, and mark the link information with the time interval information greater than the first threshold as link information that meets the requirement.

[0073] It can be understood that the present invention uses a preset static load balancing algorithm to judge and process the link to ensure that the link is unobstructed, while determining the length of the response time interval information to determine whether the response time meets the requirements, thereby ensuring the high availability of the system.

[0074] In a specific implementation of the present disclosure, step S4 includes step S41, step S42, step S43 and step S44.

[0075] Step S41, calling the flow rate of the access flow information of the intranet user terminal in the second information and the flow rate of the access flow information of the extranet user terminal;

[0076] Step S42: initiating a connection request to the IP address of the domain name, and obtaining access result information of the client by load balancing the access flow information of the external network user terminal to the client;

[0077] Step S43, allocating the traffic of the access traffic information of the intranet user terminal to the link information reaching the requirement;

[0078] Step S44: after converting the IP address of the domain name into the public network address of the corresponding ISP network segment, the traffic is sent to the internal server to obtain the access result information of the internal server.

[0079] It can be understood that the present invention improves the response efficiency of the server by converting the IP address into the corresponding public network address and then scheduling it uniformly, thereby greatly improving the availability of the server group and the application.

[0080] In a specific implementation of the present disclosure, step S3 further includes step S5, step S6 and step S7.

[0081] Step S5: Mark the link information with the time interval information less than or equal to the first threshold as link information that does not meet the requirement;

[0082] Step S6: shielding the link information that does not meet the requirements through a firewall, and sending a first command, wherein the first command is to establish a backup link in the backup load balancing device;

[0083] Step S7: sending the access flow information of the link that does not meet the requirements to the backup link for transmission, marking the access flow information of the link that does not meet the requirements, and sending a command to maintain the access flow information link to the communication equipment of the maintenance personnel.

[0084] It can be understood that the present invention establishes a backup link, and after removing the link that does not meet the requirements, the traffic in the removed link is transmitted to the backup link, thereby ensuring the normal access of the user while ensuring the correctness of the response content and preventing duplicate content.

[0085] Example 2

[0086] like Figure 2 As shown, this embodiment provides a multi-link load balancing device, which includes a first acquisition unit 701, a first processing unit 702, a second processing unit 703 and a third processing unit 704.

[0087] The first acquisition unit 701 is used to acquire first information, where the first information is the user's access traffic information and a preset static load balancing algorithm;

[0088] A first processing unit 702 is configured to send the first information to a first model for processing to obtain second information, wherein the first model is a model for classifying the traffic, and the second information is the classified traffic information;

[0089] The second processing unit 703 is used to send the second information to the second model for processing to obtain third information, wherein the second model is a model for determining whether the link accessed by the traffic meets the requirements for the classified traffic information, and the third information is the link information that meets the traffic access requirements;

[0090] The third processing unit 704 is used to send the first information and the third information to the third model to obtain fourth information. The fourth model is a model that balances the traffic load to the healthy server or client, and the fourth information is access result information of the server or client.

[0091] In a specific implementation of the present disclosure, the first processing unit 702 includes a first processing sub-unit 7021 and a second processing sub-unit 7022 .

[0092] The first processing subunit 7021 is used to classify the access flow information of the users in the first information to obtain the access flow information of the intranet user terminal and the access flow information of the extranet user terminal;

[0093] The second processing sub-unit 7022 is used to perform domain name resolution on the access flow information of the intranet user terminal and the access flow information of the extranet user terminal respectively, and obtain domain name information of at least one classified flow.

[0094] In a specific implementation of the present disclosure, the second processing unit 703 includes a first acquiring subunit 7031 , a third processing subunit 7032 , a second acquiring subunit 7033 and a fourth processing subunit 7034 .

[0095] The first acquisition subunit 7031 is used to obtain the access cache record of the domain name information of the classified traffic in the local cache;

[0096] The third processing subunit 7032 is used to determine the health of the link where the traffic is located according to whether the link in the access cache record is accessible, and process the healthy link where the classified traffic is located using a preset static load balancing algorithm to obtain the time interval information of the third model sending a query request in reverse to the LDNS to receive a response and the IP address of the domain name within a certain period of time;

[0097] The second acquisition subunit 7033 is used to acquire a first threshold value, which is a threshold value of time interval information for the third model to send a query request in reverse to the LDNS and receive a response;

[0098] The fourth processing subunit 7034 is configured to compare the first threshold with the time interval information, and mark the link information with the time interval information greater than the first threshold as link information that meets the requirement.

[0099] In a specific implementation of the present disclosure, the third processing unit 704 includes a fifth processing sub-unit 7041 , a sixth processing sub-unit 7042 , a seventh processing sub-unit 7043 and a first sending sub-unit 7044 .

[0100] The fifth processing subunit 7041 is used to call the flow rate of the access flow information of the intranet user terminal in the second information and the flow rate of the access flow information of the extranet user terminal;

[0101] The sixth processing subunit 7042 is used to initiate a connection request to the IP address of the domain name, and obtain access result information of the client by load balancing the access flow information of the external network user terminal to the client;

[0102] The seventh processing sub-unit 7043 is used to distribute the traffic of the access traffic information of the intranet user terminal to the link information reaching the requirement;

[0103] The first sending subunit 7044 is used to convert the IP address of the domain name into a public network address of the corresponding ISP network segment, and then send the traffic to the internal server to obtain access result information of the internal server.

[0104] In a specific implementation manner of the present disclosure, the second processing unit 703 further includes a fourth processing unit 705 , a fifth processing unit 706 and a first sending unit 707 .

[0105] The fourth processing unit 705 is used to mark the link information of the time interval information less than or equal to the first threshold as the link information that does not meet the requirement;

[0106] The fifth processing unit 706 is used to shield the link information that does not meet the requirements through a firewall and send a first command, where the first command is to establish a backup link in the backup load balancing device;

[0107] The first sending unit 707 is used to send the access flow information of the link that does not meet the requirements to the backup link for transmission, mark the access flow information of the link that does not meet the requirements, and send a command to maintain the access flow information link to the communication equipment of the maintenance personnel.

[0108] It should be noted that, regarding the device in the above embodiment, the specific manner in which each module performs the operation has been described in detail in the embodiment of the method, and will not be elaborated here.

[0109] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

[0110] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A multi-link load balancing method, characterized in that: include: Acquire first information, where the first information is user access traffic information and a preset static load balancing algorithm; Sending the first information to a first model for processing to obtain second information, wherein the first model is a model for classifying the traffic, and the second information is the classified traffic information; Sending the second information to a second model for processing to obtain third information, wherein the second model is a model for determining whether a link accessed by the classified traffic information meets the requirements, and the third information is link information that meets the traffic access requirements; Sending the first information and the third information to a third model, balancing the traffic load to a healthy server or client, and obtaining fourth information, where the fourth information is access result information of the server or client; The step of sending the first information to the first model for processing to obtain the second information includes: Classify the access flow information of the users in the first information to obtain the access flow information of the intranet user terminal and the access flow information of the extranet user terminal; Performing domain name resolution on the access flow information of the intranet user terminal and the access flow information of the extranet user terminal respectively to obtain domain name information of at least one classified flow; The step of sending the second information to the second model for processing to obtain the third information includes: Obtain access cache records of domain name information of classified traffic in the local cache; The health status of the link where the traffic is located is determined according to whether the link in the access cache record is accessible, and the healthy link where the classified traffic is located is processed using a preset static load balancing algorithm to obtain the time interval information of the third model sending a query request in reverse to the LDNS to receive a response and the IP address of the domain name within a certain period of time; Obtaining a first threshold value, which is a threshold value of time interval information for the third model to send a query request in reverse to the LDNS and receive a response; The first threshold and the time interval information are compared, and link information with a time interval information greater than the first threshold is marked as link information that meets the requirement.

2. The multi-link load balancing method according to claim 1, characterized in that: The sending the first information and the third information to the third model to obtain fourth information includes: Calling the flow rate of the access flow information of the intranet user terminal and the flow rate of the access flow information of the extranet user terminal in the second information; Initiate a connection request to the IP address of the domain name, and load balance the traffic information of the access traffic of the external network user to the client to obtain the access result information of the client; Allocating the traffic of the access traffic information of the intranet user terminal to the link information that meets the requirements; After converting the IP address of the domain name into the public network address of the corresponding ISP network segment, the traffic is sent to the internal server to obtain the access result information of the internal server.

3. The multi-link load balancing method according to claim 1, characterized in that: The sending the second information to the second model for processing to obtain the third information also includes: Marking link information with a time interval information less than or equal to the first threshold as link information that does not meet the requirement; The link information that does not meet the requirements is shielded through a firewall, and a first command is sent, wherein the first command is to establish a backup link in a backup load balancing device; The access flow information of the link that does not meet the requirements is sent to the backup link for transmission, the access flow information of the link that does not meet the requirements is marked, and a command for maintaining the access flow information link is sent to the communication equipment of the maintenance personnel.

4. A multi-link load balancing system, characterized in that: include: A first acquisition unit, configured to acquire first information, wherein the first information is user access flow information and a preset static load balancing algorithm; a first processing unit, configured to send the first information to a first model for processing to obtain second information, wherein the first model is a model for classifying the traffic, and the second information is the classified traffic information; a second processing unit, configured to send the second information to a second model for processing to obtain third information, wherein the second model is a model for determining whether a link accessed by the classified traffic information meets the requirements, and the third information is link information that meets the traffic access requirements; a third processing unit, configured to send the first information and the third information to a third model, load balance the traffic to a healthy server or client, and obtain fourth information, where the fourth information is access result information of the server or client; Wherein, the system comprises: A first processing subunit is used to classify the access flow information of the users in the first information to obtain the access flow information of the intranet user terminal and the access flow information of the extranet user terminal; The second processing sub-unit is used to perform domain name resolution on the access flow information of the intranet user terminal and the access flow information of the extranet user terminal respectively, and obtain domain name information of at least one classified flow; Wherein, the system comprises: A first acquisition subunit is used to obtain an access cache record of domain name information of classified traffic in a local cache; The third processing subunit is used to determine the health status of the link where the traffic is located according to whether the link in the access cache record is accessible, and process the healthy link where the classified traffic is located using a preset static load balancing algorithm to obtain the time interval information of the third model sending a query request in reverse to the LDNS to receive a response and the IP address of the domain name within a certain period of time; The second acquisition subunit is used to acquire a first threshold value, which is a threshold value of the time interval information for the third model to send a query request in reverse to the LDNS and receive a response; The fourth processing subunit is used to compare the first threshold with the time interval information, and mark the link information with the time interval information greater than the first threshold as the link information that meets the requirement.

5. The multi-link load balancing system according to claim 4, characterized in that: The system comprises: A fifth processing subunit, configured to call the flow rate of the access flow information of the intranet user terminal and the flow rate of the access flow information of the extranet user terminal in the second information; A sixth processing sub-unit is used to initiate a connection request to the IP address of the domain name, and load balance the traffic flow information of the access traffic information of the external network user end to the client to obtain the access result information of the client; A seventh processing subunit, used for respectively allocating the flow of the access flow information of the intranet user terminal to the link information that meets the requirement; The first sending subunit is used for converting the IP address of the domain name into a public network address of a corresponding ISP network segment, and then sending the traffic to an internal server to obtain access result information of the internal server.

6. The multi-link load balancing system according to claim 4, characterized in that: The system further comprises: A fourth processing unit, configured to mark link information having a time interval less than or equal to the first threshold as link information that does not meet the requirement; A fifth processing unit, configured to shield the link information that does not meet the requirement through a firewall, and send a first command, wherein the first command is to establish a backup link in a backup load balancing device; The first sending unit is used to send the access flow information of the link that does not meet the requirements to the backup link for transmission, mark the access flow information of the link that does not meet the requirements, and send a command to maintain the access flow information link to the communication equipment of the maintenance personnel.

Images