Wednesday, 18 December 2013

WiFi Direct

Wi-Fi Direct builds upon the successful IEEE802.11 infrastructure mode and lets devices negotiate who will take over the AP-like functionalities. Thus, legacy Wi-Fi devices may seamlessly connect to Wi-Fi Direct devices . By taking this decision, Wi-Fi Direct immediately inherits all the enhanced QoS, power saving, and security mechanisms.

Here's a quick guide on setting up WPS.

In a typical Wi-Fi network, clients discover and associate to WLANs, which are created and announced by Access Points (APs). In this way, a device unambiguously behaves either as an AP or as a client, each of these roles involving a different set of functionality. A major novelty of Wi-Fi Direct is that these roles are specified as dynamic, and hence a Wi-Fi Direct device has to implement both the role of a client and the role of an AP.

The device implementing AP-like functionality in the P2P Group is referred to as the P2P Group Owner (P2P GO), and devices acting as clients are known as P2P Clients.Legacy clients can also communicate with the P2P GO, as long as they are not 802.11b-only devices and support the required security mechanisms.

For example, consider a laptop accessing the Internet through a legacy infrastructure AP while at the same time streaming content to a TV set by establishing a P2P Group, where the laptop acts as P2P GO.

If the P2P GO leaves the P2P Group then the group is torn down, and has to be re-established using some of the specified procedures.

 Wi-Fi Direct devices usually start by performing a traditional Wi-Fi scan (active or passive), by means of which they can discover existent P2P Groups3 and Wi-Fi networks.

After this scan, a new Discovery algorithm is executed, which we describe next. First, a P2P Device selects one of the so-called Social channels, namely channels 1, 6 or 11 in the 2.4 Ghz band, as its Listen channel.

Then, it alternates between two states: a search state, in which the device performs active scanning by sending Probe Requests in each of the social channels; and a listen state, in which the device listens for Probe Requests
in its listen channel to respond with Probe Responses. The amount of time that a P2P Device spends on each state is randomly distributed, typically between 100 ms and 300 ms.

EAP based setup based on external registrar

Station willing to connect to AP, sends out a probe request with WPS IE, request type set to enrollee.

AP sends a Wi-Fi Simple Configuration probe response to the Registrar with
Response Type set to AP.

After this M1 to M8 exchange occurs. Enrollee (the station) may decide to associate to a WSC-enabled AP and initiate the registration protocol by sending message M1 to the Registrar; assuming that
the Registrar is not yet prepared to enroll the candidate enrollee it will respond with message M2D.

M2D – this message indicates that the Registrar is unable to authenticate with the Enrollee, but it is willing to provide descriptive information about the Registrar to the Enrollee.

Phase 1:
1. The Enrollee sends its Discovery message using an 802.11 probe request. The
Discovery message is broadcast by the AP to all external Registrars.
2. The AP responds to the probe request with its own Discovery data.
3. The Enrollee connects to the AP and initiates 802.1X.
4. The Enrollee‟s M1 message is proxied to all External Registrars as UPnP events.
Each active Registrar (Internal Registrar, if enabled, and all the External
Registrars that have subscribed to receive UPnP events from the AP) should
send M2 or M2D.
5. The two external Registrars send M2D messages to the AP. The AP queues
these up for delivery to the Enrollee.
6.The AP sequentially delivers the M2D messages to the Enrollee, which responds
with ACK messages to each one. After the last M2D has been delivered without
a WSC_MSG response, the AP sends EAP-Failure to terminate the 802.1X

Phase 2:
1. Enter PIN in ER.
2. Registrar notifies the AP when it becomes active by setting the Selected Registrar attribute to TRUE
3. After the AP receives a SetSelectedRegistrar UPnP action with Selected Registrar TRUE, AP incorporates Selected Registrar flag set to TRUE in its Beacons and Probe Responses
4. Enrollee reconnects and restarts the 802.1X authentication. This time, Registrar sends an M2 message rather than an M2D message.
5. The Enrollee and Registrar engage in the complete Registration Protocol until the
Enrollee is provisioned with its Credential.

Monday, 16 December 2013

Out-of-Band setup

In out-of-band methods there is a transfer of information by a channel other than the Wi-Fi channel itself.

  1. Near-Field-Communication Method, in which the user simply has to bring the new client close to the access point to allow a near field communication between the devices. NFC Forum compliant RFID tags can also be used. Support of this mode is optional.
  2. USB Method, in which the user uses a USB flash drive to transfer data between the new client device and the access point of the network. Support of this mode is optional, but deprecated.

The USB method has been deprecated and is not part of the Alliance's certification testing.