Sao chép không đồng bộ liên quan đến việc thực hiện cập nhật dữ liệu ở một trang web lưu trữ chính và sau đó gửi và áp dụng các bản cập nhật tương tự tại một thời gian sau các trang web khác phản ánh. Các cập nhật được gửi đi và áp dụng cho các trang web phản ánh những khoảng thời gian khác nhau. | Network Monitoring 327 degraded. They should also allow incorporation and definition of user-defined agents if needed with those widely used. Typical metrics obtained include server I O information system memory and central processing unit CPU utilization and network latency in communicating with a device. In general SNMP GET and TRAP commands are used to collect data from devices. SET commands are used to remotely configure devices. As this command can be quite destructive if improperly used it poses a high security risk and should be utilized judiciously 6 7 . Many devices use SNMP MIP but manage via Java applets and secure socket layer SSL -management Web servers. A network itself is a single point of failure for network management. Network monitoring implies communication with the network elements. Often times SNMP commands are issued inband meaning that they are sent over the production network. If the network is down then SNMP is of little use. Often an agent can indicate if communication with any other nodes has failed or if it is unacceptable. Some agents can try to fix the problem on their own. If communication is lost some agents can communicate via other nodes. Some can even assume control server tasks if communication with the server is lost. However without the ability to communicate to a failed node nothing beyond the problem notification can be done. An alternative approach is to communicate to a device via an out-of-band mechanism typically through a secure dial-up connection or SSL over dial-up through a Web server. Many network monitoring solutions focus on devices. Often information alerts regarding a device may not indicate what applications and ultimately services and transactions are going to be impacted. Network-monitoring tools should be able to help identify the impact of device problem by application. This requires the identification of resources and processes required for the operation of an application including such items as .
