PERFORMANCE

One important issue in networking is the performance of the network—how good is it? We discuss quality of service, an overall measurement of network performance.

Topics discussed in this section:

• Bandwidth
• Throughput
• Latency (Delay)
• Bandwidth-Delay Product

Bandwidth

• Bandwidth measures network performance .
• The term can be used in two different contexts with two different measuring values: bandwidth in hertz and bandwidth in bits per second.

Note

In networking, we use the term

bandwidth in two contexts.

❏ The first, bandwidth in hertz, refers to

the range of frequencies in a

composite signal or the range of

frequencies that a channel can pass.

❏ The second, bandwidth in bits per

second, refers to the speed of bit

transmission in a channel or link.

Throughput

• The throughput is a measure of how fast we can actually send data through a network.
• Although, at first glance, bandwidth in bits per second and throughput seem the same, they are different.
• The bandwidth is a potential measurement of a link; the throughput is an actual measurement of how fast we can send data.

Latency (Delay)

• The latency or delay defines how long it takes for an entire message to completely arrive at the destination from the time the first bit is sent out from the source.
• We can say that latency is made of four components: propagation time, transmission time, queuing time and processing delay.

Bandwidth-Delay Product

• Very important in data communications is the product of the two, the bandwidth-delay product.
• The bandwidth~delay product defines the number of bits that can rdl the link.

Note

The bandwidth-delay product defines

the number of bits that can fill the link.

Concept of bandwidth-delay product