Broadcast vs Unicast on an 802.11ac Wireless network

[mutantnewfie80]

We currently use UDP Broadcasts for a service in our wired network to minimize traffic as we communicate with several hundred devices. Looking at what I can find on 802.11 without paying for a copy of the standard, it appears that in the case of devices with sleeping radios, a broadcast over WiFi is really Unicast  in that the device wakes up during a beacon, checks the DTIM and then has to connect to get the missed broadcast. I assume most devices today (in this case Android Tablets) do sleep in between beacons to save battery life.

I am trying to understand if there is any advantage to using broadcast in the wireless medium as we have a customer who does not allow wireless broadcast. There is a concern among management that moving to a true Unicast would increase traffic and could cause congestion and delay on the wireless medium.

[Flavio Miranda]

Hi

 I dont believe this cause huge impact on the network design. I higly recommend you to take a look on the following document.

 Also, there was not hugh modification on 802.11ac amendment. Considering you are moving from 802.11n networ.

https://www.cisco.com/c/en/us/td/docs/wireless/controller/8-1/Enterprise-Mobility-8-1-Design-Guide/Enterprise_Mobility_8-1_Deployment_Guide/cuwn.pdf 

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[mutantnewfie80]

Thanks but I think I wasn't clear in my scenario. Our current situation is a wired network where we broadcast a packet from a server to multiple devices. These packets are small but delivery timing is important. We need these delivered within half a second.



We are now moving to a situation where we need to get this data from the server to 200-300 wireless devices in the same timeframe. My question is whether it is more efficient to send a broadcast over the wireless network or to move to a unicast scenario.

[Flavio Miranda]

Right. If time is essential then you may have problems. No way wireless latency can be lower then wired. Latency will increase two or three times in wifi environment.

 For multicast/broadcast communication, AP will use the lowest data rate, so it is important to setup data rates as high as possible. I use 12 Mbps on my environment. 

 With unicast packet you will rich your environment´s optimal speed, which means, considering 802.11ac in 5.0 Ghz, two spatial stream with good signal.

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[Leo Laohoo]

802.11 wireless networking is, in essence, a broadcast: One talks and every one else waits for their turn to "talk".
Depends on what this traffic is, if it is time-based critical, then wireless is not a solution because a lot of things can cause wireless traffic to get "lost".

[Rasika Nayanajith]

In wireless environment broadcast forwarding has been disabled by default (Controler -> General -> Broadcast forwarding). This setting will prevent, any broadcast message comes from wireless media (OTA)or wired device forwarding to another wireless clients. Therefore you can have large wireless subsets without having any negative impact on performance due to ARP broadcast.

If your application really required broadcast to be enable, you need to enable it with care as that change could have significant impact on wireless performance. Your channel utilization will go high with this change & monitor it and see. It is never recommend to enable it on a large wireless networks

HTH

Rasika

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