What is the difference between network/link Speed and Bandwidth?

Question

I did some research and some say they are same and interchangeable but some says they are different. What I understand is that Bandwidth is the amount of data carried while the Speed is the data carried at a certain rate. So, when we get Internet plan from our ISPs and they say that the speed would be, for example, 50Mbps. Is that Bandwidth or Speed? I am a little confused. Can anyone shed some light on it and make it clear? Thank you in advance

Answer 1

The 50Mbps speed would refer to raw data on the cable. Note that this is usually exporessed in bits per second. In the past there was a very direct relation to this and how fast you could change the signal on a cable.

That is raw speed, not useable bandwith. How fast you are actually getting your data is a complex story which included transfering the data and overhead.

If this is to abstract, consider the bandwith the number of letter you can type per second. The usuable bandwith has those letters and the destination on an envelope, a return address etc etc.

A good rule of thumb to compare these two are is devide the speed (in bits per second) though 10 to get to the bandwidth (in bytes per second).

Answer 2

I think the terminology you may be looking for is Bandwidth and Throughput. Speed is kind of a very generic term that can have very different meanings depending on context. In this context, speed can mean both bandwidth or throughput.

Bandwidth is the theoretical number, given the specifications of the technology being used to deliver data end to end. Theoretically, you should get 50Mbps. But there can be many conditions that affect the speed you actually get (hardware limitations, congestion, remote end's bandwidth etc etc). Sometimes you will get more, sometimes you will get less from speed tests, this speed over a period of time is your throughput.

Your maximum speed during any given unit of time is technically what it is capable of, and is theoretically the speed you should see. ISPs will always advertise Bandwidth, your speed tests will always show Throughput.

I hope this makes sense.

Answer 3

As far as I can tell they are used interchangeably. From dictionary.com:

http://www.dictionary.com/browse/bandwidth

Digital Technology. the transmission capacity of an electronic
communications device or system; the speed of data transfer:

The units of 50 Mbps refers to the amount of data carried per unit time. this would be 50 million bits per second. So the units also suggest they are used interchangeably.

There is another measure that one could relate to the "speed" and that is latency. How long it takes to make a request and receive an answer from a source on the internet over your connection. Sometimes referred to as ping.