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Both attempt to measure the speed of a network. If data rate is the thing that is commonly measure in Mbps and latency is the thing that is measured in milliseconds, what are their similarities and differences?

I've tried searching google but the explanations I get are inconsistent. After searching "network latency" the first result is wikipedia but this definition pertains more to structural engineering than networks. The second result is about.com and it states

The term latency refers to any of several kinds of delays typically incurred in processing of network data.

So does this mean latency is not a well-defined term and can mean whatever a person wants it to?

For example, when using ping what does the latency actually measure (and out of curiosity why doesn't ping tell the data rate, in Mbps)?

What is the perceived difference between latency and data rate, is it that latency only matters until the download (or uploaded) first part has been received?

  • This sounds way too much like a homework question. You may want to rephrase if it is not. – some_guy_long_gone Aug 18 '14 at 20:52
  • @legioxi ok well it's not a homework question, what is it about it that makes it look as such? – Celeritas Aug 18 '14 at 20:59
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    "what are their similarities and differences?" just came across as very homework sounding. – some_guy_long_gone Aug 18 '14 at 21:16
  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can provide your own answer and accept it. – Ron Maupin Aug 7 '17 at 16:23
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Latency is the amount of time it takes a packet of data to leave your computer and receive a response back from the end point. That is why this is measure in time. This is key for time sensitive applications like VoIP and video conferencing.

Bandwidth/data rate is the amount of data (bits) you can upload or download in a given time (seconds). This is key for downloads and uploads (i.e. video streaming for Hulu, Netflix, etc). It is also important in video conferencing as you're sending/receiving a lot of video (bandwidth) and the audio portion needs to be in near real time (latency).

Ping is sending packets using ICMP and measuring the time it takes until you receive an echo-reply from the end point. It is not sending a lot of data and would not give any accurate information regarding bandwidth.

Something like iperf may be used to measure bandwidth by sending a lot of data to the end point which also would be running perf.

You can have high latency (slow round trip time for packets) but still have a lot of bandwidth. Satellite service is one example.

  • So in a sense data rate measures a characteristic of a single device where as latency measures the relation between two devices? – Celeritas Aug 18 '14 at 21:21
  • Both measure a relationship between two devices. Data rate is measuring how much data can be sent per interval of time from one device to the other. Latency is measuring only the interval of time it takes for a packet to make a round trip. – some_guy_long_gone Aug 18 '14 at 21:31
  • Is there a formula that relates data rate and latency? For example data rate = data received/time interval = data received/(latency/2) – Celeritas Aug 18 '14 at 21:37
  • I am unaware of a formula. – some_guy_long_gone Aug 19 '14 at 3:19
  • Build your formula the other way around, it networking its called the "Bandiwdth Delay Product" - See speedguide.net/faq_in_q.php?qid=185 for examples and of course, Wikipedia en.wikipedia.org/wiki/Bandwidth-delay_product – jwbensley Aug 19 '14 at 12:34
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Latency is the delay, it is measured in units of time. Data rate is how much data can be sent per unit if time, it is not measured in data rate (per unit of time, normally a standard unit).

Data rate can affect latency in the real world, whereas latency affects bandwidth, "goodput", and I thiiink throughput.

One way to simulate data rate affecting latency is by pinging with ever-increasing packet sizes (though this has more--I believe--to do with how ICMP is handled than data rate).

One way to show data rate affecting latency is to measure latency whilst conducting a speed/bandwidth test.

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