Computer network (i) Bandwidth understanding

First, the concept of bandwidth

"Bandwidth" is bandwidth literal translation of English words. In different areas, the understanding of bandwidth is also different.

1, the field of electronic communication: refers to a certain signal has a fixed band width . In other words, the bandwidth of the signal refers to the frequency range occupied by the different frequency components contained in the signal.

　　Note : The frequency band is the concept of relative baseband, refers to the modulation can be transmitted on the channel to transmit the signal occupied by the range of frequencies, generally we also called the Pass band .

2, computer network domain: refers to the network system communication link (with the channel or the transmission media consent) the ability to transmit data, that is, to characterize the unit time from a point in the network to another point can pass the " highest data rate ."

　　Note : the "bandwidth" and "throughput" two words in the computer network are easily confused, with the following differences:

2.1) network bandwidth (bandwidth): Emphasize the network maximum data transmission rate, that is, transmission data rate theory peak.

2.2) network throughput (throughput): emphasizes the actual data transfer rate of the network.

Ii. in-depth understanding of bandwidth

1. In the field of electronic communication, the unit of bandwidth is Hertz (Hz). The passband essentially refers to the range of signal bands allowed by the communication line, so to speak, in the field of electronic communication, the bandwidth is the bandwidth of the link (channel), that is, the channel nature determines the pass band .

Categories, bandwidths and typical applications for commonly used twisted-pair wires

2, Computer networks Road field, the unit of bandwidth is bit per second (b/s). Because in the computer network domain, we are not concerned about the specific physical media, but the information transmission protocol standard. In the physical layer, we use bitstream to describe the data, which can be as much as possible to mask the difference between the transmission media and communication means, so that the data link layer on the physical layer does not feel these differences.

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　　speaking of which, you may ask: Why should the two units be different? Can't all be unified with Hertz (Hz)?

In fact, this is mainly because the traditional communication line uses the continuous change of analog signals, such as our telephone signal using the standard bandwidth is 3.1kHz(300hz~3.4khz). However, with the development and maturation of laser and optical fiber communication technology, we have to consider the unit problem of optical fiber communication technology used to describe the bandwidth. Because the optical fiber communication uses the laser pulse signal, this is a kind of discrete digital signal, it is different from the traditional continuous analog signal, therefore should not use Hz to describe the bandwidth.

The communication line is transformed into a combination of digital and analog signals by a traditional analog-only signal. Therefore, in the computer network, we will these communication lines of the difference shielding, in the physical layer Unified use B/s to describe the bandwidth.

　　Note : Communication lines are not a problem that we need to consider in our computer network, but the field of electronic communications.

Also, I think it is necessary to mention that the bandwidth in the field of electronic communication and the bandwidth in the computer network are essentially unified. It seems that the words I said may be a little abstract, specifically:

In the expression of two kinds of bandwidth, the unit uses Hz to understand from the frequency domain, while the unit uses B/S is understood from the time domain. The reader can slowly realize, have the opportunity I also will write an article to have a good talk.

Three, bandwidth and broadband discrimination

The layman often sees bandwidth and broadband as the same concept, but the two are distinct concepts. The bandwidth of English is bandwidth, and broadband can not be called wideband, but broadband.

Broadband refers to the bandwidth that reaches a certain data rate. But broadband is a dynamic development concept, that is to say, different times, because of the development of technology, broadband definition will change. The United States FCC in the January 7, 2015 annual Broadband progress report will be defined as follows: The data transfer rate reached upstream 3mbps/downlink 25Mbps bandwidth of the Internet connection called broadband.

Computer network (i) Bandwidth understanding