Fast Session Transfer (FST) is the transfer of a session from a channel
to another channel in a different frequency band. The term "session"
refers to non-physical layer state information kept by a pair of
stations (STAs) that communicate directly (i.e., excludes forwarding).
The FST is implemented in accordance with IEEE Std 802.11ad-2012.
Definitions
* FST interface - an interface for which FST functionality is enabled
* FST group - a bunch of FST interfaces representing single
multi-band STA
* FST peer - a multi-band capable STA connected
* FST module - multi-band operation functionality implemented in
accordance with IEEE Std 802.11ad-2012 (see 10.32
Multi-band operation) as a part of hostapd/wpa_supplicant
* FST manager - an external application that implements custom FST
related logic, using the FST module's interfaces
accessible via CLI or D-Bus
This commit introduces only the FST module. Integration of the FST
module into the hostapd/wpa_supplicant and corresponding CLI/D-Bus
interfaces and FST related tests are covered in separate commits.
FST manager application is out of scope of these commits.
As FST aggregates a few interfaces into FST group, the FST module uses
global CLI for both commands and notifications. It also exposes
alternative non-interface based D-Bus subtree for this purposes.
Configuration and Initialization
* FST functionality can enabled by compilation flag (CONFIG_FST)
* hostapd/wpa_supplicant controlling multiple interfaces are used for
FST
* once enabled by compilation, the FST can be enabled for specific
interfaces in the configuration files
* FST interfaces are aggregated in FST groups (fst_group_id config file
entry), where each FST group:
- represents one multi-band device
- should have two or more FST interfaces in it
* priority (fst_priority config file entry) must be configured for each
FST interface. FST interface with higher priority is the interface FST
will always try to switch to. Thus, for example, for the maximal
throughput, it should be the fastest FST interface in the FST setup.
* default Link Loss Timeout (LLT) value can be configured for each FST
interface (fst_llt config file entry). It represents LLT to be used
by FST when this interface is active.
* FST interfaces advertise the Multi-band capability by including the
Multi-band element in the corresponding frames
FST CLI commands:
* fst list_groups - list FST groups configured.
* fst list_ifaces - list FST interfaces which belong to specific group
* fst iface_peers - list Multi-Band STAs connected to specific interface
* fst list_sessions - list existing FST sessions
* fst session_get - get FST session info
* fst session_add - create FST session object
* fst session_set - set FST session parameters (old_iface, new_iface,
peer_addr, llt)
* fst session_initiate - initiate FST setup
* fst session_respond - respond to FST setup establishemnt attempt by
counterpart
* fst session_transfer - initiate FST switch
* fst session_teardown - tear down FST Setup but leave the session object
for reuse
* fst session_remove - remove FST session object
FST CLI notifications:
* FST-EVENT-PEER - peer state changed (CONNECT/DISCONNECT)
* FST-EVENT-SESSION - FST session level notification with following
sub-events:
- EVENT_FST_SESSION_STATE - FST session state changed
- EVENT_FST_ESTABLISHED - previously initiated FST session became
established
- EVENT_FST_SETUP - new FST session object created due to FST session
negotiation attempt by counterpart
All the FST CLI commands and notifications are also implemented on D-Bus
for wpa_supplicant.
IEEE 802.11 standard compliance
FST module implements FST setup statemachine in compliance with IEEE
802.11ad (P802.11-REVmc/D3.3), as it described in 10.32 Multi-band
operation (see also Figure 10-34 - States of the FST setup protocol).
Thus, for example, the FST module initiates FST switch automatically
when FST setup becomes established with LLT=0 in accordance with
10.32.2.2 Transitioning between states.
At the moment, FST module only supports non-transparent STA-based FST
(see 10.32.1 General).
Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>
Anton Nayshtut