Public-Mesh-Research-Report.md

@@ -117,11 +117,15 @@ This does not allow a group of devices to bootstrap connectivity entirely withou
 
 ### Bluetooth Low Energy (BLE)
 
-Bluetooth Low Energy is a separate protocol from Bluetooth classic that is designed to reduce the energy consumption during use, without greatly impacting functional range. 
+Bluetooth Low Energy is a separate protocol from Bluetooth classic that is designed to use less energy without greatly impacting functional range.
 
-#### BLESSED Library
+Like Bluetooth classic, BLE allows devices to discover and connect to each other. A device in the "peripheral" role sends advertisement packets and accepts connections, while a device in the "central" role receives advertisement packets and initiates connections.
 
-We have found that the open source Bluetooth library [BLESSED](https://github.com/weliem/blessed-android) is useful for working with BLE on Android. The project's README.md offers an introduction to the library for new users, and they also offer a number of [example projects](https://github.com/weliem/blessed-android/tree/master/app/src/main/java/com/welie/blessedexample) to help developers get started with BLESSED.
+Once a connection has been made, data may be exchanged using the Generic Attribute Profile (GATT). The peripheral offers one or more GATT services, each consisting of predefined "characteristics": small pieces of data that can be read or written by the central.
+
+More recently, the Bluetooth standard has defined L2CAP Connection-Oriented Channels (CoC), which allow socket-like connections between centrals and peripherals. The server socket on the peripheral device is identified by an ephemeral number called the protocol/service multiplexer (PSM), which must be communicated to the central somehow (eg through BLE advertising, GATT, or out-of-band). Android provides an API for L2CAP CoC on API levels 29 and later if the hardware supports it.
+
+Most Android phones can operate in the central role and some can also operate in the peripheral role, so some pairs of devices can make peer-to-peer BLE connections via GATT or L2CAP CoC.
 
 #### Security
 
@@ -189,6 +193,7 @@ On API level 30 and earlier, access to some Bluetooth APIs requires location-rel
 
 ### BLESSED
 
+We have found that the open source Bluetooth library [BLESSED](https://github.com/weliem/blessed-android) is useful for working with BLE on Android. The project's README.md offers an introduction to the library for new users, and they also offer a number of [example projects](https://github.com/weliem/blessed-android/tree/master/app/src/main/java/com/welie/blessedexample) to help developers get started with BLESSED.
 #### Peer Advertisement
 
 Peer advertisement happens using BLE's peripheral advertisement protocol. Peripheral devices build a schema of characteristics, and advertise their core service UUID over the Bluetooth frequency band. 
@@ -316,7 +321,7 @@ Bluetooth Mesh is a relatively new Bluetooth standard that supports multi-hop co
 * https://www.bluetooth.com/wp-content/uploads/2019/03/Mesh-Technology-Overview.pdf
 * https://www.bluetooth.com/bluetooth-resources/controlling-bluetooth-mesh-networks-with-android-applications/
 
-The mesh stack shares some lower layers with the Bluetooth LE stack in smartphones, but it also has some higher layers that aren't implemented in smartphones. So when a phone interacts with a mesh, it does so via a device called a proxy that implements both stacks. As far as we were able to tell, a mesh can't be formed from just smartphones.
+The mesh stack shares some lower layers with the BLE stack in smartphones, but it also has some higher layers that aren't implemented in smartphones. So when a phone interacts with a mesh, it does so via a device called a proxy that implements both stacks. As far as we were able to tell, a mesh can't be formed from just smartphones.
 
 There are several projects that implement the higher layers of the mesh stack in software, on Linux at least: