3 Replies Latest reply on Feb 13, 2018 10:45 PM by grsr

    Wi-Fi Roaming, flow control questions

    user_20707134

      Please respond to the following questions:

      1. Can Wi-Fi modules to provide fast switching between access points with the same SSID? What is the maximum duration of a break in data transmission by TCP when switching between access points when using WPA2-PSK and data flow of about 140 kilobytes per second?

      2. Allow the modules to control the communication quality with the access point?

      3. Allow the modules to perform background scanning of Wi-Fi networks?

      4. Keep the modules TCP connection when switching between access points?

      5. Is it possible to know how much data the module is successfully sent via TCP before the connection failed?

      6. As modules control the flow of TCP data from host?

      7. As the host controls the flow of TCP data from the module?

      Thanks.

        • 1. Re: Wi-Fi Roaming, flow control questions
          grsr

          1. To switch between access points, a STA would need to disassociate with AP and then associate with another AP and obtain Ipv4 address subsequently. This would require calling wiced_leave_ap(), wiced_join_ap_specific() and wiced_ip_up() respectively. The wiced_leave_ap() would take 1 ms and wiced_join_ap_specific() would take about 3.7s to execute. The wiced_ip_up() would depend on network stack. With NetX, it takes about 4.3s and with LwIP, it takes about 2.1s. So the total switching time with NetX is about 8s and with LwIP is 5.8s. Measurement was performed on CYW943907AEVAL1F platform. Additional time will be required to bring up the TCP server/TCP client before data transmission is resumed. You can check TCP server and client snips for reference.

           

          2. I would assume the communication quality is characterised by SNR, RSSI and throughput. The SNR would depend on band. 5 GHz band would provide better SNR over the crowded 2.4 GHz band. Throughput would depend on a number of factors such as 802.11 mode (a/b/g/n), WLAN serial interface (SDIO/SPI), noise, interference. You can consider using 802.11n mode in 5GHz band with SDIO or on-chip WLAN interface (CYW43907) to optimize the quality.

           

          3. Yes. We have a snip.scan that shows how to scan the network or you can use scan command in test.console.

           

          4. When switching between access points, the STA would need to disassociate with the AP as stated earlier. As a result, the TCP connection would not be maintained.

           

          5. You can keep track of how much TCP data is sent successfully in application code. You can register TCP callback using wiced_tcp_register_callbacks() to check when the connection failed.

           

          6. and 7. TCP resides in host which means that the host processor would control data flow.

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          • 2. Re: Wi-Fi Roaming, flow control questions
            axel.lin_1746341

            grsr wrote:

             

            1. To switch between access points, a STA would need to disassociate with AP and then associate with another AP and obtain Ipv4 address subsequently. This would require calling wiced_leave_ap(), wiced_join_ap_specific() and wiced_ip_up() respectively. The wiced_leave_ap() would take 1 ms and wiced_join_ap_specific() would take about 3.7s to execute. The wiced_ip_up() would depend on network stack. With NetX, it takes about 4.3s and with LwIP, it takes about 2.1s. So the total switching time with NetX is about 8s and with LwIP is 5.8s. Measurement was performed on CYW943907AEVAL1F platform. Additional time will be required to bring up the TCP server/TCP client before data transmission is resumed. You can check TCP server and client snips for reference.

             

            Hi grsr

            Does WICED SDK support the 802.11r standard for WiFi roaming?

            • 3. Re: Wi-Fi Roaming, flow control questions
              grsr

              Support for 802.11r fast roaming is planned for 4343x, 43364, 43340 and 4390x in WICED 6.1.

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