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I totally understand the difference between bandwidth and throughput. While bandwidth shows the maximum amount of data can be transmitted from a sender to a receiver, throughput is the actual amount of data that has been transmitted as they could be different factors such as latency affecting throughput.

Bit rate is the amount of data(number of bits) can be transmitted per second which sounds the same as throughput to me. So what is the key difference?

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Some of these terms are used differently by different people, but below is what is generally accepted.

Bandwidth is the number of bits per second that a link can send or receive, including all flows. For example, the bandwidth of a 100 Mbps connections is 100 Mbps, but that doesn't mean it is always sending or receiving 100 Mbps, but that is the maximum possible on that link. Unlike what many people mean by bandwidth, it does not mean data usage. I see people say that they have a bandwidth limitation (every link does), and they have used all their bandwidth for the month. This is an incorrect use of the term. What they mean to say is that they have a data usage limitation, and they have used it up for the month.

Throughput is the amount of data during a time period that a flow (process to process) can send or receive. This includes all the host overhead, and contention on the link (multiple flows on a link will each use some percentage of the bandwidth, reducing the throughput of each).

Bit rate is closer to bandwidth, but it is often per host, or source to destination devices. You may have a bit rate of 100 Mbps from a host to a switch, but the bit rate from a host to a host is less. This usually includes multiple flows.

  • Thanks for your reply. In order to be clear, let say, for a link that has a 100Mbps bandwidth(for all processes) , throughput could be 65 Mbps(in the particular process) depending on the overhead etc. And the bit rate between a sender host and a switch could be 100 Mbps while the bit rate another switch and a receiver is 70 Mbps for the same process. Do these assumptions sound correct? – Nara Feb 24 '17 at 22:10
  • Possibly. The bandwidth and bit rate are going to include protocol (layer-2, layer-3, and layer-4) overhead, while the throughput will not, so the throughput will be lower than the other two. The bit rate can possibly equal the bandwidth, but the bandwidth is generally considered per link in the path, while the bit rate is usually over the whole path. – Ron Maupin Feb 24 '17 at 22:16
  • So for the whole flow it is a case that 2( or even more)different bit rates can be measured, right? – Nara Feb 24 '17 at 22:24
  • Per flow, you usually look at throughput. That can translate directly to how much time it takes to download a file. The various links in the path can all have different bandwidth, some networks through which the data passes may be congested, causing losses and retransmissions, etc. What you are looking for is the average over a certain period of time it takes for application data to get from one host to another. – Ron Maupin Feb 24 '17 at 22:31
  • In that case, does the expected average equals to throughput or the average result of bit rates measured over the process? – Nara Feb 24 '17 at 23:00
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Daily I see peoples even specialists in communication do mistakes about the three mentioned terms: Bandwidth: The unit of it is Hz, so it is mathematically is: High_Used_Frequency - Low_Used_Frequency. So, when we measure bandwidth in bps, i.e we do mistake. Beside, some guys working in Network field, totally they treat with the bandwidth as Data rate. So, bandwidth is the difference between high and low frequency. For example, bandwidth of a channel in FM is 0.2MHz, for a carrier is WCDMA is 5MHz.

Data Rate: the unit is bps, so we can say the data rate of the channel is the maximum ability of the channel that can transmit bits in a second. In the normal case, we can say that if we have 5MHz bandwidth, then the channel capacity (or data rate) is 5Mbps, but also it can be that the bandwidth is 5MHz but the data rate is 10Mbps, or 2.5Mbps, this is depends on the modulation type and some other Technics. Throughput: This term is used in many different systems, shortly, and clearly we can define it as: the real data that we receive. For example, the Bandwidth=5MHz, channel capacity(data rate)=10Mbps,but what we receive exactly is 6Mpbs due to any reason, so the throughput is 6Mbps... Hope I gave you an idea...

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    You are correct, of course, but since we're almost always speaking about Ethernet, which is baseband modulated, BW = data rate. – Ron Trunk Nov 20 '17 at 18:55
  • The difference is how electrical engineering and computer science view the term. This question asks, specifically, about that. – Ron Maupin Nov 20 '17 at 19:07
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Not disagreeing with other answers, but an important takeaway is that people often are meaning slightly different things with similar and identical words.

A couple of points which are worth adding, especially if you do anything numerical like try to work out the maximum throughput of a given FTP connection over an X Mbit/sec line:

  • Kbit/sec, Mbit/sec etc in data rates are always powers of 10 as far as I have ever seen
  • File sizes are equally stated as powers of 2 and often powers of 10, and very frequently people don't even know ("few hundred megabyte" obviously doesn't matter at that accuracy.)

If you ever get your oscilloscope on the wire you'll quickly find out that the symbol rate can be different. 100baseT for example is 125 Mbaud, because it transmits 5 bits on the wire for 4 bits of data.

In summary, the terms used often vary depending on what you're emphasising:

  • Throughput really emphasises all the things which could slow it down, very much a "net result".
  • Bandwidth really emphasises the gross bit rate, and you still have to pay for all the framing and overheads before you get throughput.

You sometimes will see things like "peak throughput" and "average sustained throughput" which I'd regard as very helpful. Very often the rates that are interesting depend entirely on the period you average over.

PS IEC prefixes kibi, mebi, etc are far from universally used but worth knowing about

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I'll try to explain it very simply. BW is the range of frequencies that can pass through a channel ( Unit: Hz). Data rate is the amount of data that passes through a medium per unit time ( Unit: bits/sec). Imagine a narrow road and highway, road width as the BW and car going through as data. More BW, More data rate. So, data rate is data passing through medium. But if the data is maximum then it is equal to bandwidth. BW is the maximum data rate.

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