There are three different definitions related to network traffic utilization, and distinguishing between them is critical to understanding network bandwidth utilization:

• Speed: Maximum amount of traffic that can traverse the circuit or link.
• Bandwidth: Maximum amount of traffic (bits per second) that is allowed to traverse the link. By default, the bandwidth will be equal to the speed of the link.
• Throughput: Effective end application traffic (bits per second) that is transferred between the application endpoints.

The speed of a link (and so the bandwidth) varies depending on various factors, including the type of link, CAR offered by the provider, and local configuration. By default, most network devices will be able to forward traffic at line rate, which is the maximum supported bandwidth on the respective link.

In recent deployments, it is common to see Gigabit Ethernet as the last mile access connection from WAN routers to service providers. The speed of the Gigabit Ethernet will be 1 Gbps, but the bandwidth can vary depending on the CAR provided by the service provider.

Even if a WAN router is capable of sending traffic at line rate of the link, the service provider will ensure that the traffic does not exceed the CAR.