Networking – WiFi on 2.4GHz is slow, but 5GHz is very fast


I've been having an ongoing problem with my home WiFi network. As stated in the title, my 2.4GHz network is slow but 5GHz is perfectly fine. I've checked with a WiFi analyzer and there aren't too many other 2.4 networks around, and I'm using the recommended channel. The connection is generally spotty, sometimes seeming fine and other times dropping to a crawl.

In an attempt to combat the problem I bought a new router, and split off some of the traffic to my old router. So my network setup is:

  • main router: Netgear Nighthawk X10 R9000, on
  • child router (downstairs): TP Link Archer C3200, on

The child router is hardwired in to the main router on a cat5 cable, and broadcasts its own 2.4 and 5GHz networks, and both routers have the same problem. The main router does have other electronics nearby (AV receiver, home wireless phone, cable box, modem), but the child router has nothing nearby.

I've switched from 2.4 to 5GHz and run speed tests while 2.4 is going slow, and 5GHz is always fine.

For the most part this isn't a major problem, I'm just using 5GHz whenever I can. But I have a home security system, and those cameras only run on 2.4GHz. So whenever I connect to one of them, it complains that the network is slow, and it's difficult for me to review saved clips. Also, maybe one day in the future I'll decide to save money and switch to a cheaper internet plan, losing 5GHz entirely.

So my questions are:

  • how can this be?
  • how can I troubleshoot it / fix it?
  • could it be my ISP? (optimum online)
  • is there a way to monitor all 2.4GHz traffic and see if some massive amount of data is passing through it all the time, indicating maybe a virus on a local machine or something?

Best Answer

It's common for 5GHz speeds to be several times faster than 2.4GHz speeds due to bandwidth and congestion issues.
It's important to note that the 2.4 band is narrow and often crowded/congested, whereas the 5GHz band is broad and more open. With typical AC-capable gear in typical scenarios, it's reasonable to expect 5GHz to provide >4x the performance of 2.4GHz, especially when you're close to the AP (AP = "Access Point", which is the technical term for a wireless router's ability to create a wireless network).

Wireless speed drops off dramatically with range.
Devices that are far from the AP have to use simpler, slower signaling methods (modulation schemes) in order to be received reliably. This means they "talk so slow" that they use up a lot of airtime to move the same amount of traffic as something that's closer to the AP would use.

Wireless video cameras are generally bad news for network performance.
Because of that second point, wireless security cams, especially 2.4GHz-only ones, are generally a very poor design choice. They need high bandwidth for video streaming, but they're typically positioned far from the AP (say, under the eaves outside your house), so they have unrealistic airtime needs. It's a standard principle of good home network design that your stationary devices should always be connected via Ethernet so you save your limited, precious wireless airtime for mobile devices. This goes double for stationary devices that send or receive video, because video has fairly high bandwidth requirements.

Troubleshooting network performance requires measuring network performance.
Since you're having a network performance problem, you should be using a simple tool like IPerf to measure your network performance, so you're dealing in numbers (quantitative empirical data) and not just qualitative anecdotes. Plug a machine into your AP via gigabit Ethernet to be one IPerf endpoint. Use a wireless machine as your other IPerf endpoint. Join the wireless machine to the 2.4GHz network of that AP and use IPerf to measure performance in each direction separately (not simultaneously). Then join it to the 5GHz network of that AP and measure performance in each direction separately. Maybe repeat on the second AP. It helps to share that measured performance data, and how you measured it, whenever you ask for help with a network performance problem.

Maximum wireless performance is determined by what the AP and the client both support. A modern fast router can't send data to an older client using modern fast modulation schemes that the older client doesn't understand. So if you're having a Wi-Fi performance problem, it's not enough to look at the wireless specs of your router, you have to look at the wireless specs of your client devices as well. When asking for help with wireless performance problems, it helps to include client devices' Wi-Fi specs (or brands and exact model numbers so others can look up the detailed specs).