UNIX for Advanced & Expert Users

Sorry to keep bothering you guys like this with all these boring, related questions. But here's one that should be more readily answerable.
What command or file should i use to get the speed/data rate of a network link? This is the capacity speed for instance 10Mbps or 100 Mbps in the case of the Ethernet local area network.

Thanks.

dont you already know if it is a 10MBS network card, wont its max be 10MBS??

No, a 10 MBPS or 100 MBPS Ethernet card does not guarentee 10 or 100 MBPS.... There are many factors to consider... protocol overhead, latency in the network card and drivers, latency and speed of the network and transmission layer protocols, the speed and processing power of the application and operating system and the network traffic. Ethernet uses a version of the Aloha protocol where users transmit, collide with other transmission, and retransmit. This is not a very efficient protocol in networks, but works and is simple.