Monitor and classify your bandwidth and network usage with, PRTG - Paessler Router Traffic Grapher.
    This must have tool for monitoring and classifying network and bandwidth usage has no better replacement. You can receive bandwidth and network usage data that helps to optimize the efficiency of your network. This appication supports the SNMP, packet sniffing and netflow protocol for generating live readings and trend data. It runs on a Windows machine in your network 24 hours a day, 7 days a week, and constantly monitors and records the network usage parameters. The tool helps to: avoid bandwidth and server performance bottlenecks, find servers using your bandwidth, reduce costs by buying bandwidth and hardware as per actual load. It works with most network devices supporting SNMP, and tested with routers and switches from companies like Cisco, HP, 3Com, Linksys and DLink.
    This multipurpose application will send alerts to you via email, SMS, pager or other devices in case of any downtime.