ESP8266 datasheet(111/117 Pages) ESPRESSIF

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14. Sniffer Introduction

14.3. Phone APP

For Scenario 2, phone APP should notice:

•

Time interval of each UDP packet to be longer than 20ms

•

Two data packets can be separated by a speciﬁc packet. The speciﬁc packet works

like separative sign.

•

Packet with redundant data so that packet can verify each other.

•

Set ﬂag-packet at the beginning of sequence. Then phone APP can be cyclic

sending the whole sequence.

•

Only need to send the lowest 2 Bytes of AP’s BSSID ( MAC address ), IOT-device can

still get it. If AP will broadcast its SSID, then phone APP need not to send AP’s SSID

either. So AP beacon need to be analyzed to check if the AP will broadcast its SSID.

•

Length of UDP packet need to be multiply by 4. Because when phone APP sent a

AMPDU packet which only has one sub-frame, packet length will be ﬁlled to be a

multiple of 4.

For Scenario 1, phone APP can send packets as fast as possible.

Phone APP won’t know it is Scenario 1 or Scenario 2 for IOT_device.

14.4. IOT-device Firmware

For Scenario 2, IOT-device should notice:

•

Search the channel which has strongest signal ﬁrst, according to RSSI.

•

Filter useless packets according to RSSI. Considering 10 ~ 15db ﬂuctuations in the

air, some packets may be decline 10db or more. We could search the strongest

signal at ﬁrst, then extend the range since ﬁnd the target sequence.

•

Check the Aggregation bit of HT-SIG to distinguish AMPDU packet.

•

AMPDU packet can only be encrypt by CCMP(AES).

•

To design the length of packet that works as separative sign, different QoS, different

encryption algorithm and AMPDU packet will be a multiple of 4, all of these should be

taken into consideration.

•

Use relative value to transmit information, for example, the value that the length of

data packet minus the length of packet that works as separative sign.

Espressif

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2017.05

ESP8266 Datasheet(PDF) 111 Page - ESPRESSIF SYSTEMS (SHANGHAI) CO., LTD.

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