The impact of AWDL on Mac Wi-Fi performances
Do you have a Mac?
Are you experiencing slowness during downloads or interruptions during visios?
AWDL may have something to do with it! Doesn’t it speak to you?
However, this protocol would be involved in many Wi-Fi problems as mentioned by the company Meter or the videoconferencing platform Zoom.
Through this article, you will discover and understand the functioning of this protocol but especially its impact on network performance as well as tips to limit the side effects.
Use case
AWDL (Apple Wireless Direct Link) is a proprietary Apple protocol that allows direct and fast communication between compatible iOS and macOS devices, using their Wi-Fi card.
Its most frequent uses are AirDrop and AirPlay, where it allows you to simply discover surrounding Apple devices, in order to transfer files or multimedia content.
With it, there is no need for complex configuration, just a few clicks to establish a connection. But this ease of use can also hide problems when this protocol cohabits with high density Wi-Fi environments, such as in the enterprise.
The following services use AWDL :
- AirDrop : File transfer between iOS / macOS devices
- AirPlay : Streaming media to Apple TV, connected speakers…
- Automatic unlocking : Unlocking a Mac via an Apple Watch
- Universal clipboard : Shared clipboard between iPhone/iPad and Mac
Operation
AWDL uses the built-in Wi-Fi network card in Macs / iPhones / iPads to set up an “Ad Hoc” link with the other target device.
It’s a direct link, without going through your corporate Wi-Fi hotspots, or your box at home.
This transmission is done on the following Wi-Fi channels:
- 6 (2.4 GHz band)
- 44 (5 GHz) — preferred in European Union / EU
- 149 (5 GHz) — preferred in the US
Please note that it is not possible to select these channels manually!
In concrete terms, in Ad-Hoc mode, the two Apple devices communicate directly via AWDL, as in the case of AirDrop, for example.
On the contrary, the “Infrastructure” mode is the one used during transfers with a Wi-Fi terminal
On the macOS level, an interface named awdl0 is automatically configured, as soon as features using it are activated, even when no transfer using AWDL is in progress.
Impacts on Wi-Fi performance
As previously mentioned, AWDL uses the Wi-Fi card of your Mac, iPhone or iPad to transfer files or multimedia content.
Behind the ease of use and the magic of AirDrop, AirPlay, important questions arise especially in high-density environments, where many devices are using AWDL:
- The network card cannot transmit simultaneously to the Wi-Fi hotspot used for Internet access AND with another device using AWDL as in AirDrop.
In this case, the network card switches at regular intervals during the transmission time between the Wi-Fi channel of the terminal in infrastructure mode and the channel designated by AWDL (6,44,149)
Problems arise mainly during latency-sensitive uses (Visio, VoIP) and can create latency spikes, as the network card must constantly alternate between AWDL and the AP channel used for other uses.
- Wi-Fi channels 6, 44 and 149 used by AWDL may already be in use in your Wi-Fi terminal environment.
If your Wi-Fi hotspots are on these same channels, using AWDL can create co-channel interference (CCI).
The impact here is more significant, as it can impact not only the Apple device in use, but also all other connected clients.
Impact experimentation
Let’s experiment : in order to see the performance losses, I launched the transfer via AirDrop of a 363 MB video from an iPhone to my MacBook Pro M1, by pinging my local gateway (here 192.168.1.1).
During the AirDrop transfer, the ping is sometimes more than 200 ms, and that increase in latency that can create problems of video micro-cuts, degraded voice during Teams visios, Google Meets, WebEx or other latency-sensitive applications.
A Wireshark capture on the interface shows well the beginning and the end of the exchange, quite fast by the way (about 5s for the complete transfer)
For the more curious, the exchange is done via the IPv6 link-local addresses of the devices used:
How to better manage Apple devices on a corporate Wi-Fi network?
Don’t worry, the impact of AWDL does not usually cause problems when used in environments with few Apple devices, as the traffic generated by its use is very low.
In this case, the performance degradation will only be perceived during simultaneous use, as in the previous experiment.
However, AWDL should concern you if you are in a high-density enterprise environment, where channels are already heavily used and limited, and performance degradations can impact other users.
So there are several possible workarounds for the use of Apple devices in the enterprise:
- Limit the use of Wi-Fi channels 44 and 149
When allocating Wi-Fi channels in an environment intended to host many Apple devices, this constraint can be taken into account.
Channel 44 used in Europe is valuable, as it is one of the 4 non-DFS channels available (More details in this Medium story)
- Disable AWDL
This is not really a solution from my point of view, because it means losing many useful and appreciated features.
Theoretically, on macOS, disabling the interface created by AWDL can be done via the ifconfig awdl0 down command, but any service that needs it like AirDrop will automatically re-enable it.
In all cases, these choices are to be made according to the share of Apple devices in relation to the rest of the fleet, and to the frequency of use of the related features.
