path: root/doc/p2p.doxygen
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authorJouni Malinen <jouni.malinen@atheros.com>2010-07-18 21:30:26 (GMT)
committerJouni Malinen <j@w1.fi>2012-05-03 15:08:23 (GMT)
commitf765701faf05c1773a44865728e74cd60c6cde18 (patch)
tree77cc027b20efb53763a042cc4c288df388b5c6d2 /doc/p2p.doxygen
parentf2e03085d7f49f9455b25b2b9b0c628bd88e9606 (diff)
P2P: Add P2P information for Doxygen docs
Signed-hostap: Jouni Malinen <jouni@qca.qualcomm.com>
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+\page p2p Wi-Fi Direct - P2P module
+Wi-Fi Direct functionality is implemented any many levels in the WLAN
+stack from low-level driver operations to high-level GUI design. This
+document covers the parts that can be user by %wpa_supplicant. However,
+it should be noted that alternative designs are also possible, so some
+of the functionality may reside in other components in the system.
+The driver (or WLAN firmware/hardware) is expected to handle low-level
+operations related to P2P Power Management and channel scheduling. In
+addition, support for virtual network interface and data frame
+processing is done inside the driver. Configuration for these
+low-level operations is defined in the driver interface:
+src/drivers/driver.h. This defines both the commands and events used to
+interact with the driver.
+P2P module implements higher layer functionality for management P2P
+groups. It takes care of Device Discovery, Service Discovery, Group
+Owner Negotiation, P2P Invitation. In addition, it maintains
+information about neighboring P2P Devices. This module could be used
+in designs that do not use %wpa_supplicant and it could also reside
+inside the driver/firmware component. P2P module API is defined in
+Provisioning step of Group Formation is implemented using WPS
+%wpa_supplicant includes code in interact with both the P2P module
+(wpa_supplicant/p2p_supplicant.c) and WPS
+(wpa_supplicant/wps_supplicant.c). The driver operations are passed
+through these files, i.e., core P2P or WPS code does not interact
+directly with the driver interface.
+\section p2p_arch P2P architecture
+P2P functionality affects many areas of the system architecture. This
+section shows couple of examples on the location of main P2P
+components. In the diagrams below, green arrows are used to show
+communication paths from the P2P module to upper layer management
+functionality and all the way to a GUI that user could use to manage
+P2P connections. Blue arrows show the path taken for lower layer
+operations. Glue code is used to bind the P2P module API to the rest
+of the system to provide access both towards upper and lower layer
+\subsection p2p_arch_mac80211 P2P architecture with Linux/mac80211/ath9k
+An architecture where the P2P module resides inside the
+%wpa_supplicant process is used with Linux mac80211-based drivers,
+e.g., ath9k. The following diagram shows the main components related
+to P2P functionality in such an architecture.
+\image html p2p_arch.png "P2P module within wpa_supplicant"
+\image latex p2p_arch.eps "P2P module within wpa_supplicant" width=15cm
+\subsection p2p_arch_umac P2P architecture with UMAC
+The following diagram shows the main components related to P2P
+functionality in an architecture where the P2P module resides inside
+the kernel IEEE 802.11 stack (UMAC in the figure).
+\image html p2p_arch2.png "P2P module in kernel
+\image latex p2p_arch2.eps "P2P module in kernel" width=15cm
+\section p2p_module P2P module
+P2P module manages discovery and group formation with a single state
+machine, i.e., only a single operation per device can be in progress
+at any given time. The following diagram describes the P2P state
+machine. For clarity, it does not include state transitions on
+operation timeouts to the IDLE state. The states that are marked with
+dotted ellipse are listed for clarity to describe the protocol
+functionality for Device Discovery phase, but are not used in the
+implementation (the SEARCH state is used to manage the initial Scan
+and the alternating Listen and Search states within Find).
+\image html p2p_sm.png "P2P module state machine"
+\image latex p2p_sm.eps "P2P module state machine" width=15cm
+\subsection p2p_module_api P2P module API
+P2P module API is defined in src/p2p/p2p.h. The API consists of
+functions for requesting operations and for providing event
+notifications. Similar set of callback functions are configured with
+struct p2p_config to provide callback functions that P2P module can
+use to request operations and to provide event notifications. In
+addition, there are number of generic helper functions that can be
+used for P2P related operations.
+These are the main functions for an upper layer management entity to
+request P2P operations:
+- p2p_find()
+- p2p_stop_find()
+- p2p_listen()
+- p2p_connect()
+- p2p_reject()
+- p2p_prov_disc_req()
+- p2p_sd_request()
+- p2p_sd_cancel_request()
+- p2p_sd_response()
+- p2p_sd_service_update()
+- p2p_invite()
+These are the main callback functions for P2P module to provide event
+notifications to the upper layer management entity:
+- p2p_config::dev_found()
+- p2p_config::go_neg_req_rx()
+- p2p_config::go_neg_completed()
+- p2p_config::sd_request()
+- p2p_config::sd_response()
+- p2p_config::prov_disc_req()
+- p2p_config::prov_disc_resp()
+- p2p_config::invitation_process()
+- p2p_config::invitation_received()
+- p2p_config::invitation_result()
+The P2P module uses following functions to request lower layer driver
+- p2p_config::p2p_scan()
+- p2p_config::send_probe_resp()
+- p2p_config::send_action()
+- p2p_config::send_action_done()
+- p2p_config::start_listen()
+- p2p_config::stop_listen()
+Events from lower layer driver operations are delivered to the P2P
+module with following functions:
+- p2p_probe_req_rx()
+- p2p_rx_action()
+- p2p_scan_res_handler()
+- p2p_scan_res_handled()
+- p2p_send_action_cb()
+- p2p_listen_cb()
+In addition to the per-device state, the P2P module maintains
+per-group state for group owners. This is initialized with a call to
+p2p_group_init() when a group is created and deinitialized with
+p2p_group_deinit(). The upper layer GO management entity uses
+following functions to interact with the P2P per-group state:
+- p2p_group_notif_assoc()
+- p2p_group_notif_disassoc()
+- p2p_group_notif_formation_done()
+- p2p_group_match_dev_type()
+The P2P module will use following callback function to update P2P IE
+for GO Beacon and Probe Response frames:
+- p2p_group_config::ie_update()
+\section p2p_driver P2P driver operations (low-level interface)
+The following driver wrapper functions are needed for P2P in addition
+to the standard station/AP mode operations when the P2P module resides
+within %wpa_supplicant:
+- wpa_driver_ops::if_add()
+- wpa_driver_ops::if_remove()
+- wpa_driver_ops::alloc_interface_addr()
+- wpa_driver_ops::release_interface_addr()
+- wpa_driver_ops::remain_on_channel()
+- wpa_driver_ops::cancel_remain_on_channel()
+- wpa_driver_ops::send_action()
+- wpa_driver_ops::probe_req_report()
+- wpa_driver_ops::disable_11b_rates()
+The following driver wrapper events are needed for P2P in addition to
+the standard station/AP mode events when the P2P module resides within
+- wpa_event_type::EVENT_RX_ACTION
+- wpa_event_type::EVENT_REMAIN_ON_CHANNEL
+- wpa_event_type::EVENT_RX_PROBE_REQ
+The following driver wrapper functions are needed for P2P in addition
+to the standard station/AP mode operations when the P2P module resides
+in the driver or firmware:
+- wpa_driver_ops::if_add()
+- wpa_driver_ops::if_remove()
+- wpa_driver_ops::alloc_interface_addr()
+- wpa_driver_ops::release_interface_addr()
+- wpa_driver_ops::disable_11b_rates()
+- wpa_driver_ops::p2p_find()
+- wpa_driver_ops::p2p_stop_find()
+- wpa_driver_ops::p2p_listen()
+- wpa_driver_ops::p2p_connect()
+- wpa_driver_ops::p2p_reject()
+- wpa_driver_ops::wps_success_cb()
+- wpa_driver_ops::p2p_group_formation_failed()
+- wpa_driver_ops::p2p_set_params()
+The following driver wrapper events are needed for P2P in addition to
+the standard station/AP mode events when the P2P module resides in the
+driver or firmware:
+- wpa_event_type::EVENT_P2P_DEV_FOUND
+- wpa_event_type::EVENT_P2P_GO_NEG_REQ_RX
+- wpa_event_type::EVENT_P2P_GO_NEG_COMPLETED
+\section p2p_go_neg P2P device discovery and group formation
+This section shows an example sequence of operations that can be used
+to implement P2P device discovery and group formation. The function
+calls are described based on the P2P module API. The exact design for
+the glue code outside the P2P module depends on the architecture used
+in the system.
+An upper layer management entity starts P2P device discovery by
+calling p2p_find(). The P2P module start the discovery by requesting a
+full scan to be completed by calling p2p_config::p2p_scan(). Results
+from the scan will be reported by calling p2p_scan_res_handler() and
+after last result, the scan result processing is terminated with a
+call to p2p_scan_res_handled(). The P2P peers that are found during
+the full scan are reported with the p2p_config::dev_found() callback.
+After the full scan, P2P module start alternating between Listen and
+Search states until the device discovery operation times out or
+terminated, e.g., with a call to p2p_stop_find().
+When going into the Listen state, the P2P module requests the driver
+to be configured to be awake on the listen channel with a call to
+p2p_config::start_listen(). The glue code using the P2P module may
+implement this, e.g., by using remain-on-channel low-level driver
+functionality for off-channel operation. Once the driver is available
+on the requested channel, notification of this is delivered by calling
+p2p_listen_cb(). The Probe Request frames that are received during the
+Listen period are delivered to the P2P module by calling
+p2p_config::p2p_probe_req_rx() and P2P module request a response to
+these to be sent by using p2p_config::send_probe_resp() callback
+function. If a group owner negotiation from another P2P device is
+received during the device discovery phase, that is indicated to the
+upper layer code with the p2p_config::go_neg_req_tx() callback.
+The Search state is implemented by using the normal scan interface,
+i.e., the P2P module will call p2p_config::p2p_scan() just like in the
+full scan phase described. Similarly, scan results from the search
+operation will be delivered to the P2P module using the
+p2p_scan_res_handler() and p2p_scan_res_handled() functions.
+Once the upper layer management entity has found a peer with which it
+wants to connect by forming a new group, it initiates group owner
+negotiation by calling p2p_connect(). Before doing this, the upper
+layer code is responsible for asking the user to provide the PIN to be
+used during the provisioning step with the peer or the push button
+press for PBC mode. The glue code will need to figure out the intended
+interface address for the group before group owner negotiation can be
+Optional Provision Discovery mechanism can be used to request the peer
+to display a PIN for the local device to enter (and vice versa). Upper
+layer management entity can request the specific mechanism by calling
+p2p_prov_disc_req(). The response to this will be reported with the
+p2p_config::prov_disc_resp() callback. If the peer device started
+Provision Discovery, an accepted request will be reported with the
+p2p_config::prov_disc_req() callback. The P2P module will
+automatically accept the Provision Discovery for display and keypad
+methods, but it is up to the upper layer manegement entity to actually
+generate the PIN and to configure it with following p2p_connect() call
+to actually authorize the connection.
+The P2P module will use p2p_config::send_action() callback to request
+lower layer code to transmit an Action frame during group owner
+negotiation. p2p_send_action_cb() is used to report the result of
+transmission. If the peer is not reachable, the P2P module will try to
+find it by alternating between Action frame send and Listen
+states. The Listen state for this phase will be used similarly to the
+Listen state during device discovery as described above.
+Once the group owner negotiation has been completed, its results will
+be reported with the p2p_config::go_neg_completed() callback. The
+upper layer management code or the glue code using the P2P module API
+is responsible for creating a new group interface and starting
+provisioning step at this point by configuring WPS Registrar or
+Enrollee functionality based on the reported group owner negotiation
+results. The upper layer code is also responsible for timing out WPS
+provisioning if it cannot be completed in 15 seconds.
+Successful completion of the WPS provisioning is reported with a call
+to p2p_wps_success_cb(). The P2P module will clear its group formation
+state at this point and allows new group formation attempts to be
+started. The upper layer management code is responsible for configuring
+the GO to accept associations from devices and the client to connect to
+the GO with the provisioned credentials. GO is also responsible for
+calling p2p_group_notif_formation_done() as described below.
+If the WPS provisioning step fails or times out, this is reported with
+a call to p2p_group_formation_failed(). The P2P module will clear its
+group formation state at this point and allows new group formation
+attempts to be started. The upper layer management code is responsible
+for removing the group interface for the failed group.
+\section p2p_sd P2P service discovery
+P2P protocol includes service discovery functionality that can be used
+to discover which services are provided by the peers before forming a
+group. This leverages the Generic Advertisement Service (GAS) protocol
+from IEEE 802.11u and P2P vendor-specific contents inside the Native
+GAS messages.
+The P2P module takes care of GAS encapsulation, fragmentation, and
+actual transmission and reception of the Action frames needed for
+service discovery. The user of the P2P module is responsible for
+providing P2P specific Service Request TLV(s) for queries and Service
+Response TLV(s) for responses.
+\subsection p2p_sd_query Quering services of peers
+Service discovery is implemented by processing pending queries as a
+part of the device discovery phase. p2p_sd_request() function is used
+to schedule service discovery queries to a specific peer or to all
+discovered peers. p2p_sd_cancel_request() can be used to cancel a
+scheduled query. Queries that are specific to a single peer will be
+removed automatically after the response has been received.
+After the service discovery queries have been queued, device discovery
+is started with a call to p2p_find(). The pending service discovery
+queries are then sent whenever a peer is discovered during the find
+operation. Responses to the queries will be reported with the
+p2p_config::sd_response() callback.
+\subsection p2p_sd_response Replying to service discovery queries from peers
+The received service discovery requests will be indicated with the
+p2p_config::sd_request() callback. The response to the query is sent
+by calling p2p_sd_response().
+\subsection p2p_sd_indicator Service update indicator
+P2P service discovery provides a mechanism to notify peers about
+changes in available services. This works by incrementing Service
+Update Indicator value whenever there is a change in the
+services. This value is included in all SD request and response
+frames. The value received from the peers will be included in the
+p2p_config::sd_request() and p2p_config::sd_response() callbacks. The
+value to be sent to the peers is incremented with a call to
+p2p_sd_service_update() whenever availibility of the local services
+\section p2p_go P2P group owner
+This section describes how P2P module can be used for managing
+per-group information in a group owner. The function calls are
+described based on the P2P module API. The exact design for the glue
+code outside the P2P module depends on the architecture used in the
+When a P2P group interface is created in group owner role, per-group
+data is initialized with p2p_group_init(). This call provides a
+pointer to the per-device P2P module context and configures the
+per-group operation. The configured p2p_group_config::ie_update()
+callback is used to set the initial P2P IE for Beacon and Probe
+Response frames in the group owner. The AP mode implementation may use
+this information to add IEs into the frames.
+Once the group formation has been completed (or if it is skipped in
+case of manual group setup), p2p_group_notif_formation_done() is
+called. This will allow the P2P module to update the P2P IE for
+Beacon and Probe Response frames.
+The SME/MLME code that managements IEEE 802.11 association processing
+needs to inform P2P module whenever a P2P client associates or
+disassociates with the group. This is done by calling
+p2p_group_notif_assoc() and p2p_group_notif_disassoc(). The P2P module
+manages a list of group members and updates the P2P Group Information
+subelement in the P2P IE based on the information from the P2P
+clients. The p2p_group_config::ie_update() callback is used whenever
+the P2P IE in Probe Response frames needs to be changed.
+The SME/MLME code that takes care of replying to Probe Request frames
+can use p2p_group_match_dev_type() to check whether the Probe Request
+frame request a reply only from groups that include a specific device
+type in one of the clients or GO. A match will be reported if the
+Probe Request does not request a specific device type, so this
+function can be used to filter or received Probe Request frames and
+only the ones that result in non-zero return value need to be replied.
+When the P2P group interface for GO role is removed,
+p2p_group_deinit() is used to deinitialize the per-group P2P module
+\section p2p_ctrl_iface P2P control interface
+%wpa_supplicant \ref ctrl_iface_page "control interface" can be used
+to manage P2P functionality from an external program (e.g., a GUI or a
+system configuration manager). This interface can be used directly
+through the control interface backend mechanism (e.g., local domain
+sockets on Linux) or with help of wpa_cli (e.g., from a script).
+The following P2P-related commands are available:
+- \ref ctrl_iface_P2P_FIND P2P_FIND
+- \ref ctrl_iface_P2P_STOP_FIND P2P_STOP_FIND
+- \ref ctrl_iface_P2P_CONNECT P2P_CONNECT
+- \ref ctrl_iface_P2P_LISTEN P2P_LISTEN
+- \ref ctrl_iface_P2P_GROUP_REMOVE P2P_GROUP_REMOVE
+- \ref ctrl_iface_P2P_GROUP_ADD P2P_GROUP_ADD
+- \ref ctrl_iface_P2P_PROV_DISC P2P_PROV_DISC
+- \ref ctrl_iface_P2P_SERV_DISC_REQ P2P_SERV_DISC_REQ
+- \ref ctrl_iface_P2P_SERV_DISC_RESP P2P_SERV_DISC_RESP
+- \ref ctrl_iface_P2P_REJECT P2P_REJECT
+- \ref ctrl_iface_P2P_INVITE P2P_INVITE
+The following P2P-related events are used:
+- \ref ctrl_iface_event_P2P_EVENT_DEVICE_FOUND P2P-DEVICE-FOUND
+- \ref ctrl_iface_event_P2P_EVENT_GO_NEG_REQUEST P2P-GO-NEG-REQUEST
+- \ref ctrl_iface_event_P2P_EVENT_GO_NEG_SUCCESS P2P-GO-NEG-SUCCESS
+- \ref ctrl_iface_event_P2P_EVENT_GO_NEG_FAILURE P2P-GO-NEG-FAILURE
+- \ref ctrl_iface_event_P2P_EVENT_GROUP_STARTED P2P-GROUP-STARTED
+- \ref ctrl_iface_event_P2P_EVENT_GROUP_REMOVED P2P-GROUP-REMOVED
+- \ref ctrl_iface_event_P2P_EVENT_SERV_DISC_REQ P2P-SERV-DISC-REQ
+- \ref ctrl_iface_event_P2P_EVENT_SERV_DISC_RESP P2P-SERV-DISC-RESP
+\subsection p2p_wpa_gui GUI example (wpa_gui)
+wpa_gui has an example implementation of a GUI that could be used to
+manage P2P operations. The P2P related functionality is contained
+mostly in wpa_supplicant/wpa_gui-qt4/peers.cpp and it shows how the
+control interface commands and events can be used.
+\subsection p2p_wpa_cli wpa_cli example
+wpa_cli can be used to control %wpa_supplicant in interactive
+mode. The following sessions show examples of commands used for
+device discovery and group formation. The lines starting with "> " are
+commands from the user (followed by command result indication) and
+lines starting with "<2>" are event messages from %wpa_supplicant.
+P2P device "Wireless Client":
+> p2p_find
+> <2>P2P-DEVICE-FOUND 02:40:61:c2:f3:b7 p2p_dev_addr=02:40:61:c2:f3:b7
+pri_dev_type=1-0050F204-1 name='Wireless Client 2' config_methods=0x18c
+dev_capab=0x1 group_capab=0x0
+<2>P2P-GO-NEG-REQUEST 02:40:61:c2:f3:b7
+<2>P2P-GO-NEG-REQUEST 02:40:61:c2:f3:b7
+> p2p_connect 02:40:61:c2:f3:b7 pbc
+<2>P2P-GROUP-STARTED sta0-p2p-0 client DIRECT-vM
+> interface
+Available interfaces:
+> p2p_group_remove sta0-p2p-0
+<2>P2P-GROUP-REMOVED sta0-p2p-0 client
+> term
+P2P device "Wireless Client2" (which ended up operating in GO role):
+> p2p_find
+<2>P2P-DEVICE-FOUND 02:f0:bc:44:87:62 p2p_dev_addr=02:f0:bc:44:87:62
+pri_dev_type=1-0050F204-1 name='Wireless Client' config_methods=0x18c
+dev_capab=0x1 group_capab=0x0
+> p2p_connect 02:f0:bc:44:87:62 pbc
+> interface
+Available interfaces:
+> p2p_group_remove sta1-p2p-0
+<2>P2P-GROUP-REMOVED sta1-p2p-0 GO
+> term