What is bandwidth? How is it measured?
Introduction
You might have heard about units such as “Mbps” (megabits/sec.), “MB/s” (megabytes/sec.) and even “Gbps” (gigabits/sec) through your Internet Service Provider — these are used to measure how much data, or “bandwidth” flows between two different devices. These units are often used interchangeably, but some have very different meanings: if your home connection was “1 Gbps” (one gigabit/s), and you write “1 GB/s,” you’d be misrepresenting your maximum data throughput by a factor of 8! (1 gigabyte/s = 8 gigabit/s)
Having said that, units that have the “/[time unit]” notation after their data size represent an average of how much data is being transferred/read over the period of time. In the case of copying a local file, one might see “100 MB/s” — this means that, on average, you are copying the file back onto a drive at an average of one hundred megabytes per second. This is not a measure of size — rather, it measures an average at any instantaneous point in time.
Total Data Transferred (ex. "Bandwidth Used")
When you request an image, for example, you receive image data. This image data has a size — this size is generally measured in byte-based units (megabytes, gigabytes, even terabytes).
Using CDNs -- or Content Delivery Networks -- as an example: suppose an Edge Server will receive your request, and perform necessary processing. When the server begins to return data, it is considered “egress.”
Egress is most often the metric used for measuring usage as content delivery networks don’t tend to have a lot of ingress by end-users; the only ingress usually occurs when a CDN pulls data from an origin server.
In short, the measure of total data transferred is the amount of data moved during a given time (egress + ingress). Some providers choose to measure only ingress for "bandwidth" -- regardless, it is important to make sure you understand that data transfer, in general, measures the amount of information you've sent/received over a longer period of time (exp. terabytes transferred a month).
Data Rate or Throughput
In the previous section, "bandwidth" refers to how much data has been transferred over a longer period of time. Data rate, or data throughput, is different -- it refers to a more instantaneous transfer speed. In other words, if we had a "highway," bandwidth in this context would refer to the theoretical amount number of cars that could flow per unit of time.
Conversion Chart
For reference, all units used in this article will be in the chart below: 1 GB = 1000 MB = 1000000 KB (used to measure total data transfer, rather than an average of data being transferred at a given point)
Measuring transfer speeds:
1 Gbit/second = 1000 Mbit/s 1 Mbit/second = 1000 Kbit/s
Measuring total data transferred:
1 TB = 1000 GB 1 GB = 1000 MB 1 MB = 1000 KB
Conversion from bytes -> bits = (total_bytes) * 8
Conversion from bits -> bytes = (total_bits) / 8
