With the advent of opensource the development time has come down hugely and the quality has improved quickly. For all those involved with WLAN/Wi-Fi and Opensource lets take a look at the wlan architecture in linux based on opensource mac80211 framework.
Block diagram explaining linux WLAN architecture. Please see below for details.
User-Space:
Configuration: wpa_supplicant and hostapd:
All the applications which interact directly with the user lie here. They can a GUI/CLI based ones for eg. network manager in ubuntu/fedora distributions are UI based ones, but the core part are the CLI based ones eg. wpa_supplicant for controlling the STA part of it and hostapd for controlling the AP part.
Both are configuration file based along with their cli versions (wpa_cli, hostapd_cli) to send commands on the fly.
They support different features like SME, MLME, Security, Wifi-Direct (P2P), AP and STA configurations.
Tools:
We also have tools to send commands to the driver directly to set some parameters such as channel, bandwidth, some custom commands etc.The Bridge: User and Kernel
Now how the various applications in userspace communicate to the core entities in the kernel? Well, we have different approaches but all are based on different socket interfaces.
- WExt ==> Generic Wireless Extensions: IOCTL Interface
- NL80211==> Netlink Sockets
- HostAP,==> Raw Packet Sockets
- Chipset specific:
- Atheros==> IOCTL Interface
- Prism,IPW etc.
Kernel Space
Configuration and UMAC
For opensource world the framework in kernel for WLAN is mac80211, it separates itself in to 2 kernel modules
- cfg80211.ko: Which handles all the configuration, user space interaction
- mac80211.ko: Protocol: Upper MAC , driver interaction.
Most of the features and management is handled by the mac80211 module with the help of lower MAC.
Lower MAC Drivers
Lowe MAC drivers act as a bridge between the UMAC and the chipset (Firmware and HW). They do all the device initialization, registration with OS, Bug Registration, Interrupts registration etc through the services provided by the linux kernel.
A well written driver follows these conventions
- Maintains a OS Independent Layer: Easy portability to different OSes.
- Maintains a UMAC Independent Layer: Easpy portability to different UMAC's: Proprietary, opensource, 3rd party etc.
- Bus Abstraction Layer: Maintains compatibility across different Physical Buses like PCI, PCIe, AHB, SDIO etc.
Chipset: Firmware and HW
The full 802.11 protocol functionality is implemented here.
The firmware which probably runs on a separate processor/micro-controller configures and controls the hardware and also interacts with the host(The driver) through a messaging interface specific to the chipset (control path)
The Data path generally involves a DMA controller in the HW which takes care of generating interrupts to the host processor and transferring packets to and from the Host to the HW queues.
References:
- wpa_supplicant_hostapd_devel_doc
- For details on these click userspace_configurations.
- wpa_supplicant
