Computer network performance in the first chapter of computer network examination in 2016.6.5

1.8 Computer Network Performance Index

(1) rate (bit rate or data rate)

Bit is the unit of the amount of data in a computer and the amount of information used in information theory. This means "a binary number", so a bit is a 1 or 0 of the binary numbers.

When the data rate is high, you can use KB/S (k=10 3 times = thousand), MB/s (m=10 6 square = trillion)

(2) Bandwidth

① bandwidth originally refers to the band width of a signal. The bandwidth of the signal refers to the frequency range occupied by the various different frequency components contained in the signal. From 300Hz to 3.4KHz, the standard bandwidth of the phone signal is 3.1KHz.

For a long time in the past, the backbone of the communication is transmitting analog signals (i.e., continuously changing signals). Therefore, the signal band range that is allowed to pass through the communication line is called the bandwidth of the line.

② in a computer network, bandwidth is used to represent the ability of a network's communication link to transmit data, so the network bandwidth represents the "highest data rate" that can be passed at a point in the network over a unit of time to the other.

(3) Throughput

Throughput represents the amount of data that passes through a network (or channel, interface) within a unit of time. A measure of a real-world network.

(4) Delays (delay or delay)

① Send delay: The time required for the data frame sent by the host or router. Transmit delay = data frame Length (b)/transmit rate (/b). Send time delay occurs in the internal transmission of the machine (typically in a network adapter)

② propagation delay: propagation delay = channel Length (m)/propagation rate of the electromagnetic wave on the channel (/s). Propagation delay occurs in the media of the transmission channel outside the machine.

③ processing delay: The host and Router will take a certain amount of time to deal with when the packet is received, analyze the header of the packet, extract the data part from the packet, make the error test or find the appropriate route.

④ Queueing delay: packets are transmitted over the network through many routers, but packets are queued in the input queue after they enter the router. After the router has determined the forwarding interface, it also waits to be queued for forwarding in the output queue.

⑤ Total Delay = time delay + propagation delay + processing delay + Queue delay

⑥ The above formula shows that: the higher the data transmit rate, the faster the transmission. This is because the total delay of the data transmission is composed of four time-delay in the formula, and cannot only consider sending delay one item.

(5) Easy to confuse:

* * For high-speed network links, we are only raising the data transmission rate, not the bit on the link propagation rate.

* * The propagation rate of the electromagnetic wave on the communication line is not related to the transmitting rate of the data.

* * Increasing the data transmission rate only reduces the transmission delay of the data.

* * Often referred to as "high transmission rate of Fibre Channel" is the speed of transmitting data to the fiber channel can be very high, and the transmission rate of the fiber channel is actually lower than the transmission rate of copper wire.

(6) Delay bandwidth Product = propagation delay * Bandwidth

The propagation delay of a link is also known as the length of the link in bits.

(7) Round trip Time RTT

RTT, which indicates the total amount of time that has passed since the sender sent the data to the sender to receive confirmation from the receiver.

(8) utilization

Utilization has two kinds of channel utilization and network utilization.

Channel utilization indicates that a certain channel has a percentage of the time that is exploited (with data passed).

Network utilization is the weighted average of channel utilization in the whole network.

Channel utilization is not as high as possible. High channel or network utilization can result in very large latency. When the network utilization is close to the maximum of 1 o'clock, the latency of the network tends to be infinitely large.

(9) Non-performance characteristics of computer network

① Fee

② Quality

③ standardization

④ Reliability

⑤ Scalability and Scalability

⑥ easy to manage and maintain

Computer network performance in the first chapter of computer network examination in 2016.6.5