Many of you, on some occasions, will have noticed that the WiFi connection has too high a latency, especially if we compare it with the latency that we will get via cable. When we connect via cable, the connection latency (the time it takes for a packet to go from our PC to the router) is usually 1ms and even lower, however, via WiFi we can find good latencies of 3-4ms, even at latencies greater than 100ms in some cases. Today in this article we are going to explain why this happens, and how we can mitigate this frequent problem.
Why do I have high latency on WiFi?
Before we start talking about why I have high latency in WiFi networks, we should know a little about how the wireless WiFi networks that we all use regularly work.
Wireless WiFi networks use the CSMA / CA network access control protocol (Carrier Sense Multiple Access with Collision Avoidance) , that is, they make use of multiple access by carrier detection and collision avoidance. This protocol is essential because it allows multiple stations (such as wireless clients) to use the same transmission medium (in this case, air). Each team involved in the communication announces its intention to transmit before doing so, in order to avoid possible collisions of the frames in the air. Thanks to this behavior, we will avoid frame collisions and their subsequent retransmission. In case someone is transmitting, a random time is waited to reduce the probability of new collisions.
Basically the communication process in WiFi networks consists of three steps, first we listen to see if the network is free, if it is free we transmit the information, and finally, we wait for the confirmation of the receiver indicating that it has received everything correctly. CSMA / CA solves some typical problems in wireless networks:
- “Hidden” WiFi clients: a client might believe that the channel is free, when in fact it is not because another client is transmitting and this client does not “hear” it.
- Exposed WiFi clients: A client might believe that the channel is busy, when in fact it is not because the other client does not interfere with the communication.
In WiFi networks up to WiFi 5, we make use of OFDM (orthogonal frequency division multiplexing) , this technology allows multiplexing a set of carrier waves of different frequencies, where each one carries information and is modulated in QAM or PSK. In WiFi 5 networks, the quadrature amplitude modulation is 256QAM, while in the latest WiFi 6 standard it supports up to 1024QAM, therefore, we can send more data per symbol in the latest standard. In WiFi 6 networks, OFDMA (orthogonal frequency division multiple access) technology is incorporated, which is a huge improvement over the OFDM we had so far, OFDMA technology is the OFDM “multi-user”, allowing us to share the spectrum of a certain channel, these are called subcarriers or subcarriers, and are ideal for low speed applications. The channel is divided and divided into groups according to the needs of wireless clients, greatly optimizing WiFi wireless networks when we have dozens of clients connected.
High latency in a WiFi network can be due to several reasons, in some cases only one reason can be given, and in other cases there could be each and every one of the reasons that we are going to indicate.
We are far from the WiFi router or AP
When we are very far from the WiFi router or AP we have low coverage, this means that the packet will take longer to get from our WiFi client to the WiFi router or AP. The most important thing when we are very far from the access point, is that, normally there are other WiFi clients transmitting, so we will have to “wait” until the channel is free for us to broadcast, so it could cause latency is higher than normal, and even that there are collisions and we have to retransmit the packet.
In addition, a very important detail is that the “slower” customers hurt the faster ones, because they take longer to send their package. When we are very far from the WiFi router or AP, the synchronization speed will drop, and we will have less real speed, therefore, this must also be taken into account.
Many WiFi clients connected at the same time
When there are many WiFi clients simultaneously connected to a WiFi router or AP, the wireless network will be more collapsed, and we will have to wait longer until the channel is free to be able to broadcast. The new routers incorporate technologies such as MU-MIMO and OFDMA that allow to improve this aspect enormously, creating groups to transmit (MU-MIMO) at the same time, and creating subcarriers (OFDMA) to serve all clients.
When we have many WiFi clients connected at the same time to the same router or AP, regardless of whether they are in “stand-by”, they will always be transferring some data, so the channel occupation will be greater, and we will have a greater collapse in the wireless network, therefore, we will have to “wait” until the channel is free to be able to broadcast. In this case it is the same as before, if we have many WiFi clients, it is possible that some clients are “slow” either due to their type of WiFi network card or because they have little coverage, and this will affect the rest of the network.
There is a technology called ” Airtime Fairness ” that allows the WiFi router or AP to provide a certain time to each of the wireless clients to be able to broadcast, in this way, when we are in an environment with a mixture of fast and slow clients, we can improve the performance of the fastest clients because they will not be interrupted by the slowest clients, speeding up and reducing the latency of the WiFi connection. This feature is ideal in environments where there are dozens of wireless clients connected.
WiFi clients transferring a lot of data
If we have one or more WiFi clients transferring a lot of data, it will be more difficult to find a “hole” in the wireless network for us to be able to broadcast our packet, therefore, the latency will increase without being able to do anything. When we have a wireless client or several that do not stop sending and receiving data, the other wireless clients will be harmed because they will have to wait longer until they can transmit. This could be mitigated by performing a bandwidth control per connected wireless client, so that the same WiFi client is not able to occupy all the available channel time, in this way, the latency of the WiFi connection will decrease.
Interference with other WiFi networks and frequency bands
If our WiFi router or AP is transmitting on the same WiFi channel as other neighboring networks, we could have interference with both your router or AP, as well as your WiFi clients because they will be “occupying” air time. These interferences could also cause high latency because our customer will have to wait until the network is free.
The 2.4GHz band has a greater range than the 5GHz band, this is a clear problem for interference with the WiFi networks of neighbors. If we use the 2.4GHz band, it is very likely that we will have more interference with neighboring WiFi networks, and, therefore, we will have higher latency in the connection. If we use the 5GHz band (which has less range), surely we will not have interference with neighboring networks, or at least, we will not have so much interference with neighboring WiFi networks, therefore, if you want to have the best latency you should always use the band of 5GHz. Soon we will have available the 6GHz band thanks to the WiFi 6E, this will allow us to reduce the interference of the WiFi networks enormously by having a new frequency band.
As you have seen, these are the reasons why we could have a high latency in our WiFi connection, now we are going to give you some solutions to mitigate the problem (because surely you cannot solve it completely).
Solutions to mitigate the problem of having high latency in WiFi
If you are far from the router
If you are far from the WiFi router or WiFi access point, the best thing you can do is get closer to the AP that is broadcasting, in this way, you will have better coverage, higher synchronization speed, higher performance and lower latency. In the case that you are a WiFi network administrator, we recommend that you activate the Airtime Fairness functionality, to prevent these “slow” clients that are so far from the AP, harming the faster clients that are close to the access point . Also, it might be a good decision to use the disconnect functions for WiFi clients that are too far away, in order to kick them out of the WiFi network and not harm others.
If there are many WiFi clients connected at the same time
In the case that there are many WiFi clients connected at the same time to the same WiFi router or AP, we have two ways to make this more bearable and not affect latency. The first thing we can do is activate the “Airtime Fairness”, so that slow clients do not harm faster clients. Another option is to install an additional access point to distribute the load of the wireless clients, or a WiFi Mesh system with simultaneous triple band to have a frequency band specifically for the interconnection of the nodes (if it allows Ethernet backhaul much better), In this way, we will be distributing all the wireless clients among several nodes, performing a load balancing.
If you have clients transferring a lot of data
In the event that you have clients transferring a lot of data, it is best to limit the maximum bandwidth per wireless client, for example, put each WiFi client connected to our network to download at 50Mbps symmetric speed, in this way, we will avoid that a wireless WiFi client monopolizes all the WiFi bandwidth of the network. In addition, in this case it would also be advisable to enable Airtime Fairness to prevent slow clients from damaging the faster ones, and to optimize the wireless network as best as possible.
Use 5GHz or 6GHz and change channels if necessary
In the event that you are using the 2.4GHz band to connect, we recommend connecting to the 5GHz band or to the future 6GHz frequency band, in order to have as little interference as possible. In the event that you have interference, changing the WiFi channel will also improve the latency of the connection, in addition, in the event that you use very large channel widths such as 40MHz in 2.4GHz or 80MHz in 5GHz, possibly if you reduce the width of channel (at the cost of reducing the maximum real speed) you will have less interference with other WiFi networks.
As you have seen, depending on the scenario where we will find ourselves, we can perform different actions in order to improve the latency of our WiFi connection.