Troubleshooting Wi-Fi Slowness (Part 2.1 – Bandwidth vs Throughput vs Speed)

In part 1, I briefly discussed the 3 components that will impact the Wi-Fi performance. In these 2.X posts, I will focus on the first component, the Wi-Fi client. But first, let’s clarify some confusing terms to make sure we are all discussing the same thing.

Bandwidth vs Throughput vs Speed

These 3 terms are many times used interchangeably but they actually mean different things.

• Bandwidth: is the maximum amount of data transfer per second that is possible over this transmission channel. For example, Gigabit Ethernet can provide 1000 Mbps while Fast Ethernet can provide 100 Mbps . When we say bandwidth, think maximum theoretical capability, meaning in theory this is what we can possibly get. The unit is some “bits per second”. Bandwidth, in another context, also refers to how wide is the channel that we are using. You will hear wireless engineers saying 20MHz or 40MHz or 80MHz or 160MHz. Note that unit here is in “Hertz” and not “bits per second”. This “bandwidth” range will definitely impact the maximum “bandwidth”, meaning the maximum data transfer rate that we can achieve. With wider channels, more data can be transmitted in the same time and thus the higher the “bandwidth”.
• Throughput: is the actual amount of data transferred divided by the time taken to complete the transfer. When we say throughput, think about maximum measured capability, meaning what we are actually getting in practice. It is also measured in “bits per second”.
  Another closely related term is Goodput. The difference between the two is in the “data” part. In throughput, we are measuring all the data that is transferred (including the protocols overhead and re-transmissions) while in Goodput we are only measuring useful data. For example, if we are transferring a file we are only consider the file size in Goodput calculations and not the overhead from TCP/IP stack.
• Speed: is a consumer friendly concept to explain how fast the network is. Many people interchange bandwidth or throughput with speed. Many people read the datasheet of the Access Point and expect the “marketing” data rates of the access points to be the actual speed that they will get on Wi-Fi. However, this fallacy will be explained once we discuss the Access Point Capabilities.

Based on the above, what we really would like to measure usually is the real throughput of the network. This will be the real measurement to identify if we are getting the proper speeds as perceived by the clients. In part 2.2, we will establish a baseline by comparing wired to wireless.