*Tech Article* Theoretical wireless rate and actual wireless rate
The theoretical speed of each protocol can be referred to the following table:
Let’s use the 5Ghz 802.11n and 802.11ac as an example:
- 802.11n: The maximum theoretical rate is 600 Mbps.
- 802.11ac: The maximum theoretical rate is 6.93 Gbps.
The theoretical rate does not always equate to the actual speeds that you will see in every day use. This is usually attributed to two factors that will be discussed below.
1. Link Rate (Negotiation Rate)
When the client device connects to the Access Point, there is a negotiation phase. The following will show the relationship between theoretical rate and the negotiation rate. The negotiation rate represents the maximum theoretical rate that can be achieved between the wireless client and the Access Point. This rate is not a fixed value, but it is related to the following factors:
- Physical interference during transmission
In the transmission process when the Access Point sends a wireless signal to the wireless client, interference which often comes from noise created by other wireless routers, cordless phones, baby monitors, etc. Obstructions which are physical obstacles like walls and trees or large metal objects such as a refrigerator, will greatly affect the range, strength and quality of a wireless signal. The level of interference will lower the negotiated rate in the end.
- Hardware specifications for Access point and wireless clients
The maximum wireless speed exists for each wireless device. If the maximum wireless rate supported by the AP or wireless client is low, the maximum negotiation rate between AP and client is correspondingly low. In a real world setting, you can achieve the maximum negotiation rate by being a few meters from the router which would equate to the maximum theoretical rate.
2. Actual wireless transmission loss
The actual wireless rate generally only reaches 75% of the negotiation rate between the client and the router and can only reach 30% to 50% in an environment with large wireless interference. The factors that affect the actual wireless rate as follows:
- Amount of users
The available bandwidth in the same wireless network is shared among all users. The more bandwidth other users occupy at the same time, the slower the actual rate of the remaining users gets.
- Co-channel interference/Adjacent channel interference
If other Access Points are broadcasting their own wireless signal that happens to be in the same channel or partially overlapping frequencies, that will affect your wireless performance.
- Necessary loss of network communication
The following is a simplified OSI reference model:
In referencing the chart above, when a user sees any data, they are looking at the Application Layer. The other network layers that users do not see is what the 802.11 wireless standard utilizes which adds additional overhead. This overhead further affects the total wireless performance.
When you take into consideration the various overhead from the remaining network layers and add the actual transmission rate being 75% of the maximum theoretical rate. You begin to see how the speed that a user finally receives is a result of variables that users are commonly not aware of.
The chart below show a single client that has been tested in a “perfect” environment with the least amount of interference, and ideal distance. Although, every client will likely not be in the most ideal setting, this at least shows a real world result of the wireless performance.