iOS MTU size why only 185 bytes

[Constantin]

Hi,

I am writing an APP for comunicating with my nRF peripheral. I've set the MTU size to 251 and this works fine under bluez or android.

But if I try it in iOS (>10.0) I get only 185 bytes. Is there any way to increase it with DLE (data length extension).

So far the internet says no, but as I studied the BLE 4.2 standard it should be possible?

Best regards,

C.W.

[hmolesworth]

We found this information a while back:

iPhone iOS 8 has a maximum MTU size of 135 bytes, iOS 9 158 bytes and iOS 10 185 bytes, I found a workaround which increases iOS 10 MTU size to 247 bytes which I will test with and update Git.

trouble is I don't remember what the workaround was .. or even if it actually worked.

Maybe look at this link

[Constantin]

Mh I've tested the solution below the link but it did not solve the issue. Still I am only getting 185 bytes.

<debug> ble_gatt: Requesting to update ATT MTU to 247 bytes on connection 0x0.
<debug> ble_gatt: Requesting to update data length to 251 on connection 0x0.
<info> app: Connected to 54:A1:E4:F9:F9:52
<debug> ble_gatt: ATT MTU updated to 185 bytes on connection 0x0 (response).
<info> app: Data len is set to 182 bytes.
<info> app: p_evt->conn_handle: 0x0
<debug> app: ATT MTU exchange completed. central 0xF7 peripheral 0xF7
<debug> app: BLE_GATTC_EVT_EXCHANGE_MTU_RSP
<debug> ble_gatt: Data length updated to 27 on connection 0x0.
<debug> ble_gatt: max_rx_octets: 27
<debug> ble_gatt: max_tx_octets: 27
<debug> ble_gatt: max_rx_time: 328
<debug> ble_gatt: max_tx_time: 328
<debug> app: ATT MTU exchange completed. central 0xF7 peripheral 0xF7