display in real time the network traffic speed

 The Color Bandwidth Meter (CBM) is a small program to display the traffic
 currently flowing through the network devices in a simple curses-based GUI.
 The traffic for all interfaces include values as receive, transfer and total
 Bytes/s or bits/s (or its multiples as KB/s and Kb/s).
 .
 It is useful for Internet or LAN speed tests, measuring the velocity of a
 link, to establish a benchmark or to monitor your connections. CBM can be
 used with virtual, wired or wireless networks.