Interface graphs-Provide real-time monitoring of your bandwidth usage for each interface. Bandwidth usage is displayed for incoming and outgoing communications. You can view packet rates, counts, and errors, as well as bit, byte, and collision counts, and more.
check the section "Monitoring>Interface Graphs" in the document present in the following url:
http://www.cisco.com/en/US/docs/security/pix/pix63/pdm30/olh/PDF_Version_-_PDM_OLH/pdm30olh.pdf
