According to US patent 20180083858A1, AWDL was designed as a successor to the unsuccessful Wi-Fi IBSS a.k.a. ad hoc mode:

The limitations of IBSS mode (and its Wi-Fi infrastructure predecessors) led the Wi-Fi Alliance to define Wi-Fi Direct. Further, due to concerns regarding Wi-Fi Direct, Apple Wireless Direct Link (AWDL) was developed by Apple and eventually adopted by the Wi-Fi Alliance as the basis for Neighbor Awareness Networking (NAN).

How does AWDL work?

In technical terms, we found that AWDL works essentially works as follow:

In short, each AWDL node announces a sequence of Availability Windows (AWs) indicating its readiness to communicate with other AWDL nodes. An elected master node synchronizes these sequences. Outside the AWs, nodes can tune their Wi-Fi radio to a different channel to communicate with an access point, or could turn it off to save energy.

We published an Wireshark dissector for AWDL if you are interested in the frame format details or if you want to know which other protocols might use AWDL.

Which services use AWDL?

We compiled a non-exhaustive list with applications which use (✓) or do not use (✗) AWDL, an access point (AP) network, or Bluetooth Low Energy (BLE). We mark entries that require further investigation with (?). If you have updates, feel free to contact us.

Service AWDL AP BLE Comment
AirDrop Exchange files between two adjacent devices.
Wi-Fi Password Sharing Uses “a similar mechanism to AirDrop.
AirPlay ? Stream media to an Apple TV, HomePod, etc.
CarPlay ? ? ? Apparently uses iPhone’s hot spot function.
Auto Unlock Unlock Mac with Apple Watch. Uses AWDL to enable direct communication for ranging process. Part of Continuity framework.
Handoff Each Mac, iPhone, iPad, or iPod touch has Wi-Fi turned on” is not a requirement. Part of Continuity framework.
Universal Clipboard Part of Continuity framework.
iPhone Cellular Calls Requirement: “Each device is connected to the same network using Wi-Fi or Ethernet.” Part of Continuity framework.
Quick Start Transfers complete backup from one device to another. Device discovery is done via BLE.
Setup Apple TV ? ? ?