A low latency wireless network for 200+ users?

I'm developing a mobile application with realtime voice communication between two device in the same local wireless network. Our biggest challenge is to have a minimum latency during this conversation between 2 devices at a time.

For now, we are working on a local wireless network : only smartphones and the server.

We are currently making some test with the ASUS RT-AC87U. Without any internet connection, we can have a 50+ devices connexion without any problem. Bandwidth is near zero for all the devices, besides the two in realtime voice communication (20kbps u/d, UDP). Latency stays below 100ms.

When we plug an internet connection in the router, things get difficult. Since all devices start using bandwidth for others online app, we can't provide a low latency anymore (300-500ms peaks).

This bring me some questions :

1) When internet is on, and lot of devices use bandwidth (+- 4Mbps global), QoS priority on local UDP don't seems to help (configuration: all UDP, on a range ports used by the application, for every users 192.168.1.*). UDP bandwidth for the communication is near 20kbps, really small. Router says CPU utilisation near 20%. Jitter buffer still increase a lot near 200-300ms, instead of 30ms. What's wrong? Is it all because of interferences on the wifi signal? NOTE: Realtime voice communication is always between one fixed device (but we can't fix an IP), and one of the others devices at a time.

2) If we want to increase the amount of users near 200. Do we need more than just a few more AP and a powerful router?

I can bring more informations if needed. Thank you very much for your help/advices, I really appreciate.

Best regards, Pierre-Louis.

Pierre-Louis

Posted 2015-10-13T16:11:01.337

Reputation: 11

"Maybe limit the bandwidth per user?" - This would just make your application slower on said device. Use several high-end routers all connected to a a high performance switch. Honestly you are far exceeding the limits of these commercial mass produced home routers with 200 clients by about 175 clients. – Ramhound – 2015-10-13T16:14:49.227

You'll need to clarify where you are applying the QoS - QoS on the internet connection won't make any difference if the congestion is on the wireless. Secondly, you'll realistically want a few more WAPs. Even the fastest router in the world won't help if most devices aren't capable of the latest standards, in which case a dozen £20 routers will give better and more consistent performance than a single £200 router. Finally, you should look into WMM, it's sole purpose is to do exactly what you describe. – qasdfdsaq – 2015-10-13T16:27:50.060

QoS is set on local UDP transmission (192.168.1.*, UDP, range ports). Indeed, that doesn't help the congestion on the wireless. Does a bandwidth limitation per user can help the congestion? I was thinking about 3 good AP on 3 different channels (1,6,11). Since a good AP can support, on paper, 75-100 users... – Pierre-Louis – 2015-10-15T09:22:07.520

You'll need to apply QoS at the wireless layer. A good controller with specific VOIP support would be the easiest "out of the box" solution. Tweaking WMM controls on open-source firmware is another option, but not easy. The only way to provide reliable QoS on VoWLAN solutions is to have the wireless driver itself provide it. – qasdfdsaq – 2015-10-15T14:47:52.990

You're right about the wifi without internet, that's why we want to offer (even a small) internet access. But that's need to be controlled since we stil need to ensure a low latency during local communication. I'll check on AP and controller. On dual-band AP, if 2.4Ghz and 5Ghz are named the same SSID, does devices will be connected on both automatically? Does the AP manage which device goes on 2.4, which one goes on 5? Thanks. – Pierre-Louis – 2015-10-15T09:34:54.017

A low latency wireless network for 200+ users?

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