Briefly describe the four key indicators of network performance: bandwidth, latency, jitter, and packet loss rate

1. Bandwidth

(1) Basic concepts

Bandwidth refers to the amount of data that a network can transmit per unit time, and it reflects the network's ability to transmit data. Simply put, just as the width of a road determines the number of vehicles that can pass through it in a certain period of time, network bandwidth determines the amount of data that can be transmitted. It is usually measured in bits per second (bps), such as the common Mbps (megabits per second) and Gbps (gigabits per second).

(2) Calculation method

• The unit of bandwidth is bit/second (bit/s), where bit is the basic unit of information, representing a binary bit, that is, 0 or 1. Second (s) is the basic unit of time.
• Bits/second indicates the number of bits transmitted per second, i.e. the data transmission rate;
• 1Mbps=103 Kbps=106 bps.

2. Latency

(1) Basic concepts

Latency is the time it takes for data to travel from the sender to the receiver. Think of it like the time it takes for a package to get from one place to another. It is usually measured in milliseconds (ms).

(2) Components

Delay = sending delay + propagation delay + processing delay + queuing delay

Note: The sum of the network device processing and queuing delays can also be regarded as the "store-and-forward delay" of the network device.

(3) Simple calculation

Round Trip Delay (RTT): You can use the Ping command to test the round trip delay. Assumptions:

• The time it takes for host A to send a data packet to host B is t1;
• The time it takes for host B to respond to the data packet is t2;

The round trip delay is t1 + t2. For example, if the Ping command returns in 50ms, then the round trip delay is 50ms.

3. Packet Loss Rate

(1) Basic concepts

Packet loss rate refers to the ratio of the number of data packets lost during data transmission to the total number of data packets sent. Data packets are like letters transmitted in the network, and packet loss is like the loss of letters. It is usually expressed as a percentage.

(2) Simple calculation

Assuming that N packets are sent and M packets are successfully received, the packet loss rate = [(N - M) ÷ N] × 100%. For example:

100 packets were sent and only 95 were received. The packet loss rate = [(100 - 95) ÷ 100] × 100% = 5%.

4. Jitter

(1) Basic concepts

Jitter refers to the degree of variation in delay, that is, the difference in delay time between adjacent data packets. It reflects the stability of network delay. If delay is regarded as the driving time of a car, jitter is the fluctuation of each driving time, measured in milliseconds (ms).

(2) Simple calculation

Assume that three packets are sent consecutively, the delay of the first packet is t1 (ms), the second is t2 (ms), and the third is t3 (ms). Then the jitter can be measured by calculating the absolute value of the delay difference between adjacent packets, such as:

• The jitter between the first and second packets is |t2 - t1| (ms)
• The jitter between the second and third packets is |t3 - t2| (ms)