Please enable JavaScript.

Coggle requires JavaScript to display documents.

Wi-Fi Networking Roaming (iOS (802.11k, 802.11r 및 802.11v를 지원하는 iOS 기기…

- - - - iPhone 4s 및 이후 모델
        
        iPad Pro 및 이후 모델
        
        iPad Air 및 이후 모델
        
        iPad mini 및 이후 모델
        
        iPad (3rd generation) 및 이후 모델
        
        iPod touch (5th generation) 및 이후 모델
    - - iPhone 6s 및 이후 모델
        
        iPad Pro 및 이후 모델
        
        iPad (5th generation)
        
        iPad (6th generation)
    - - iPhone 5c, iPhone 5s 및 이후 모델
        
        iPad Pro 및 이후 모델
        
        iPad Air 및 이후 모델
        
        iPad mini 2 및 이후 모델
        
        iPad (5th generation)
        
        iPad (6th generation)
        
        iPod touch (6th generation)
- - - - 802.11k assists the device in its search for nearby APs that are available as roaming targets by creating an optimised list of channels. When the signal strength of the current AP weakens, device will scan for target APs from this list.
      - 802.11r authenticates more quickly through Fast Basic Service Set Transition (FT).
      - 802.11v allows the network’s control layer to influence client roaming behaviour by providing it the load information of nearby access points. Device takes this "BSS transition management" information into account when deciding among the possible roam targets.
  - - - 802.11r or Fast BSS Transition (FT) seeks to reduce the length of time of lost connectivity between the STA and the DS during a BSS transition. The FT protocols are part of the Re-Association service, and they only apply to STA transitions between APs within the same mobility domain of the same ESS.
        IEEE 802.11r specifies FT between access points by redefining the security key negotiation protocol, allowing both the negotiation and requests for wireless resources (similar to RSVP but defined in 802.11e) to occur in parallel.
        The key negotiation protocol in 802.11i requires the client to renegotiate its key with a RADIUS or other authentication server supporting Extensible Authentication Protocol (EAP) on every handoff for a 802.1X-based authentication, which is a time-consuming process. To save time, part of the key derived from server is cached in the wireless network, which allows a reasonable number of future connections to be based on the cached key instead of re-running 802.11X process every time.
      - The non-802.11r BSS transition takes the following steps.
        
        Run a roaming scan and find an AP for roaming.
        
        Exchange 802.11 Authentication messages with the target access point, first from the client, then from the AP.
        
        Exchange Re-Association messages to establish connection at the target AP.
        
        Start 802.1X/EAP authentication and derive a Master Session Key (MSK).
        
        Derive the Pairwise Transient Key (PTK) by using the 802.11i 4-Way Handshake of session keys to create a unique encryption key for the association base on the Master Session Key.
      - FT follows the same procedure except for the 802.1X negotiation where it piggybacks the PTK exchanges with the 802.11 Authentication and Re-Association messages instead.
    - - Neighbor Report
        
        As explained in partial scanning section, the mobile device maintains a roaming channel list to reduce scan time. But, there are cases where the device may trigger a full-scan in order to find a roaming AP. In the following diagram, the mobile device initially finds AP1 and AP2 and saves CH 1 and CH 35 in the roaming channel list after connecting to AP2.
        When the mobile device moves from Location1 to Location2, roaming will be triggered at point, Trigger1 due to a weak RSSI value. While the mobile device tries to find a roaming candidate in CH 1 and CH 36 via a partial scan, it is not able to find any other AP from the list other than AP2. Only after a full-scan will the mobile device discover AP3 and AP4 where it will add CH 11 and CH 46 into its roaming channel list after it connects to AP4.
        Having neighbor reports avoids full-scans from such instance from happening. Initially, mobile device will save CH 1 and CH 36 in the channel list as it connects to AP2, which is equal to previous case. Then, in addition, it will also send a neighbor report request to AP2. AP2 will return a list of nearby AP’s, which is AP1, AP2 and AP4. From this response, mobile devices will add CH 11 in its roaming channel list.
        As the mobile device moves away from Location 1 to Location2, the device will run a partial roaming scan at Trigger1 for CH 1, CH 11 and CH 36. This time, the device finds AP4 from its partial scan and successfully connects to AP4. After roaming success, mobile device will repeat the steps by sending a neighbor request to AP4.
      - Beacon Report
        
        APs may support roaming by sharing its neighbor list or BTM request. These requests serve as a list of recommended roaming candidates for the client devices. However, if this information is incorrect, it may disorient mobile devices’ roaming decisions. To suggest the best roaming candidate to a client, AP may receive other APs’ distances from its device client through a beacon report.
        When mobile device receives a beacon report request, it will run a scan to collect beacon frames with their respective signal strengths and return it to the AP. The AP then, can choose the best roaming AP by combining internal information with the received beacon report.