Based on the requirement, we propose this architecture. The main compo-nents of this architecture are:
• Web server
• Jabber server
• Agent
• Database
Figure 4.1 shows the basic architecture.
4.2.1 Web Server
Web server is the front end interface in this architecture. It receives the request of the browser from the administrator and makes the correspond request to the remote agent. After the agent response, the web server trans-forms the output to the web page and response to the administrator.
The advantages of the web based management system are:
• There is at least one browser installed on almost every computer. By using the browser as the front end management interface, the admin-istrator can manage the access point in front of any computer with internet connected, no matter where the administrator is. The admin-istrator does not have to install a front end management application in the computer.
• The browser is an application which is independent of the management system. All management functions are provided by the web server. If there are some modifications in the management system, for example, adding a new management function, we only would alter the server side pages. There are no modifications in the client side.
The information that the web server can provide to the administrator may possibly as whether the status of one access point is. Furthermore, there should be a map of one building displayed on the browser and mark the position of access points. When there is an error detected, the position of the failed access point should be pointed out on the map. The administrator can go to the position pointed to do the recovery. The web interface should provide the function that can add/remove monitored access point to control the scale of managed devices
Figure 4.1: The basic architecture of wireless monitoring system
4.2.2 Jabber Server
When error occurs on the access point, there should be “someone” to tell the administrator about this problem. Agent is “someone”, and Jabber server is in charge of the warning message delivery.
Using Jabber to report the warning message, there are some advantages:
• Instant message service is a real time service in the processing of mes-sage. When error occurs on the access point, the administrator will receive this event immediately if he is online.
• Administrator can see if the agent is online. If agent is online, it implies that the agent is working in condition; else if the agent is offline, the agent might not work normally. The administrator should check the status of the agent.
• Instant messaging service is a popular service in the recent years. It is very common that a instant messaging service client is working in the background at any time. The administrator would connect the instant messaging service, and set the status online, and then passively receive the notification. He need not connect to management system ad check the status of each access point.
• Jabber is a flexibly and scalable service. By relaying with a gateway, message can be redirected to other communication protocol such as SMTP or Short Message Service (SMS).
• Jabber client is an application which is independent of the management system, just like the browser. If there are some modifications about messaging notification in the management system, agent would only care about what message should send to the administrator. The client side would not do any modification.
4.2.3 Agent
Agent is the core of the whole management and monitoring system. The functionality of the agent would include:
• Detecting the status of access points by polling.
• Inform the administrator when error occurs on the access point.
Due to the structure of access points deployed in NCTU campus, each administrator in the hotspot would setup an agent to consistently monitoring
the access points in this area. Web server would connect to the agents and make requests. Agent gets dynamic information (for example, the traffic of the access point) from access points directly, or static information (for example, the IP address of the access point) from the database. At last, the agent responses the information to the web server.
In the initialization time, the agent login to the Jabber server with a predefined account. The roster in this account includes all Jabber IDs of administrators. When error detected, the agent will send a message to all administrators on the roster. In the common days with no errors, the status of the agent would be informed to administrators through the presence of the agent.
Access points in each hotspot are associated in the bridge mode. Clients get IP address from DHCPD behind the access points, and access points are also assigned a private IP to preserve the IPv4 address. We can not connect to the access points directly from the public network. Therefore, the environment where the agent locates is a gateway that can connect both private network and public network.
We choose SNMP and ICMP[9] as the protocol to simultaneously manage these access points. To those access points that support SNMP, we try not to lose their capability. From the information SNMP agent provides, we can have a better understanding about the status of the access point. To other access points that do not support SNMP, we make ICMP echo requests by ping command to receive their ICMP echo response.
4.2.4 Database
Database provides the static information about all access points. For exam-ple, IP address, location, capability (ability to support SNMP), etc. When the agent starts up, it has to get the information to understand the targets it monitors and manages. As the ability of the management system grows up, the database may also help the agent to store the monitoring result. For ex-ample, the status of access points in the last two weeks. Combined with data mining techniques, those monitoring result can provide some information to administrators.
4.2.5 Summary
In this system, we need a web server to interact with the administrator;
Database stores information like position, status of all access points; Agent consistently detects the status of the access point; Jabber server receives and relays message to administrators after agent detect the error. Web server,
database, and Jabber server do not need to exist in three physical machines.
However, the agent must exist in the private network where access points locate, and it must be able to communicate with web server and Jabber server. So the agent usually exists in the gateway.