DLE support from Android BLE 4.2 working but DLE Support from Windows BLE5.0 negotiation fails.

Question

android large mtu.pcapng hp pavilion ble 5.pcapng 
 
 After the MTU size exchange of 247 bytes with Android LL_LENGTH_REQ/LL_LENGTH_RSP are exchanged with 123 byte octets for TX and RX. Data flows properly after that. 
 But with Windows, after the MTU size exchange of 247 bytes an LL_LENGTH_REQ is sent with 251 byte octet. No LL_LENGTH_RSP is sent by Nordic from the nRF52832 
 and no further data exchange takes place.

bjorn-spockeli · Accepted Answer

Hi Mark, 
 thanks for the trace. I forgot to ask which S132 version are you using? Looking at the trace its pretty clear that the nRF is not replying to the LL_LENGTH_REQ. 
 Can you confirm that sd_ble_gap_data_length_update() returns NRF_SUCCESS when its called on the BLE_GAP_EVT_DATA_LENGTH_UPDATE_REQUEST event? I assume that you do not get the BLE_GAP_EVT_DATA_LENGTH_UPDATE event after calling sd_ble_gap_data_length_update()? 
 I also noticed that things break when its the nRF that sends the MTU Exchange Request, but when the Intel device( Central) initiates the MTU Exchange, then things proceed as normal. 
 Comparing 0743.hp pavilion large mtu 02-25-20.pcapng with default mtu size.pcapng, I cant really see why the nRF does not respond to the LL_LENGTH_REQ in the 0743.hp pavilion large mtu 02-25-20.pcapng when it does this in the default mtu size.pcapn. The LL PDU order is exactly the same in both traces. 
 Is this behavior 100% consistent, i.e. if you leave set the ATT MTU size higher than the default value then the negotiation Data length or ATT MTU negotioation halts every time? 
 Could you try to add an even longer delay in on_connected_evt() just before the call to sd_ble_gattc_exchange_mtu_request()? Like a full second or more? We want to see if the nRF replies to the LL_LENGTH_REQ then and if the Intel device then initiates the MTU Exchange procedure.

DLE support from Android BLE 4.2 working but DLE Support from Windows BLE5.0 negotiation fails.

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