Introduction to Computer Network Speed

Bandwidth in computer networking refers to the data rate supported by a network connection or interface. Network bandwidth is not the only factor that contributes to the perceived speed of a network. A lesser known element of network performance - latency - also plays an important role.
What Is Network Bandwidth?

Bandwidth is the primary measure of computer network speed. Virtually everyone knows the bandwidth rating of their modem or their Internet service that is prominently advertised on network products sold today.
In networking, bandwidth represents the overall capacity of the connection. The greater the capacity, the more likely that better performance will result. Bandwidth is the amount of data that passes through a network connection over time as measured in bits per second (bps).

Bandwidth can refer to both actual and theoretical throughput, and it is important to distinguish between the two. For example, a standard dial-up modem supports 56 Kbps of peak bandwidth, but due to physical limitations of telephone lines and other factors, a dial-up connection cannot support more than 53 Kbps of bandwidth (about 10% less than maximum) in practice. Likewise traditional Ethernet networks that theoretically support 100 Mbps or 1000 Mbps of maximum bandwidth, but this maximum amount cannot reasonably be achieved due to overhead in the computer hardware and operating systems.

Broadband and Other High Bandwidth Connections

The term high bandwidth is sometimes used to distinguish faster broadband Internet connections from traditional dial-up or cellular network speeds. Definitions vary, but high bandwidth connections generally support data rates of minimum 64 Kbps (and usually 300 Kbps or higher). Broadband is just one type of high bandwidth network communication method.
Measuring Network Bandwidth

Numerous tools exist for administrators to measure the bandwidth of network connections. On LANs (local area networks), these tools include netperf and ttcp. On the Internet, numerous bandwidth and speed test programs exist, most available for free online use.
Even with these tools at your disposal, bandwidth utilization is difficult to measure precisely as it varies over time depending on the configuration of hardware and characteristics of software applications including how they are being used.