A good monitoring tool provides this information in a graphical format upon request and at predefined intervals. To exceed thresholds at these times does not suggest a network is in dire straits. It only illustrates the impact that certain processes and applications have on a network as a whole and allows you to plan for such peaks. By comparing baselines at regular intervals, you can identify and act upon bandwidth creep and hot spots before they reach a critical state. This is the essence of proactive vs. reactive network management.
Alerts come into play at the next level of network monitoring, as problems escalate.
Audible alerts are handy if a management console is monitored 24-7. If that's not the case at your site, you'll want to look for more flexible notification techniques, such as user-defined scripts capable of dialing a pager or cellular telephone number. The most useful user-defined scripts can sort alerts based on the nature of the problem and immediately direct the most critical alerts to senior support staff, for example. Many monitoring and alerting tools go even further, offering suggestions for correcting the network fault that triggered an alert. Look for monitoring software that offers Web-based reporting with secured logon access.