S132 v3 Exchange MTU (LE Data Packet Length Extension does't work)

RE: S132 v3 Exchange MTU (LE Data Packet Length Extension does't work)

Petter Myhre — Wed, 21 Sep 2016 09:49:52 GMT

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RE: S132 v3 Exchange MTU (LE Data Packet Length Extension does't work)

eyeye — Wed, 21 Sep 2016 00:37:56 GMT

Very appreciate for your reply and patient. now I understand where is my problem, i thought LL_LENGTH_REQ was sent by S132, it's a big mistake. It's really iPhone haven't support DLE, just mtu exchanging. Thank you for all your replies above.

RE: S132 v3 Exchange MTU (LE Data Packet Length Extension does't work)

RK — Tue, 20 Sep 2016 10:23:19 GMT

From what I recall from the Apple Bluetooth list when someone asked about DLE, they said it's not supported, so not a bug at Apple, and not, as expected, a bug in S132. It's going to be interesting when more products do start supporting long MTU and DLE to work out what the most efficient length to request is, it's not always the longest possible, that can cause connection events to terminate more quickly because there's not time for full-length DLE-extended packet, so sometimes a smaller link-layer packet and a bit of fragmentation does better.

RE: S132 v3 Exchange MTU (LE Data Packet Length Extension does't work)

Keton — Tue, 20 Sep 2016 07:56:39 GMT

@eyeye sniffer traces you've posted show that iPhone 6 doesn't support DLE as it responds LL_UNKNOWN_RSP to nordic's LL_LENGTH_REQ. Note that GATT server/client is a different concept from central/peripheral denoted on sniffer traces master/slave. Most notably GATT server - the nRF is a slave device on sniffer.

So not a bug in S132, maybe a bug in iPhone if Apple intended to support DLE. Also I've done some reading around and as far as user testimonials go Nexus 5x is the only device I could find confirmation of DLE.

I also found this article: www.argenox.com/.../ denying iPhone support for DLE.

RE: S132 v3 Exchange MTU (LE Data Packet Length Extension does't work)

Elias — Tue, 20 Sep 2016 06:06:58 GMT

Agreed. I see no reason to assume that the iPhone supports DLE, or even that it has its own equivalent of a BLE_GATTS_EVT_EXCHANGE_MTU_REQUEST handler.

RE: S132 v3 Exchange MTU (LE Data Packet Length Extension does't work)

RK — Mon, 19 Sep 2016 00:23:28 GMT

Any many things it may be, a bug in s132 is the least likely. Unless you are connecting two nrf52 boards the other side most likely doesn't support data packet extensions.

RE: S132 v3 Exchange MTU (LE Data Packet Length Extension does't work)

eyeye — Sun, 18 Sep 2016 23:57:29 GMT

I think the key point is I found that nRF52 response the LL_LENGTH_REQ cmd with LL_UNKNOWN_RSP. It should be LL_LENGTH_RSP with a BLE_EVT_DATA_LENGTH_CHANGED event to the app layer. It make me giving up to solve it by myself, maybe a bug in the s132.

Use iPhone connect to S132, the nordic sniffer doesn't parse the LL_LENGTH_REQ packet, you can reference to Bluetooth Core.

RE: S132 v3 Exchange MTU (LE Data Packet Length Extension does't work)

eyeye — Sun, 18 Sep 2016 23:50:10 GMT

@RK Thanks for your reply!

Yes, Data Packet Extension is what i want to do indeed;
Change the MTU is achieved.;
Data Packet Extension is Failed (according to the sniffer, long ATT packet fragmented into short LL packet in l2cap layer);

RE: S132 v3 Exchange MTU (LE Data Packet Length Extension does't work)

RK — Sun, 18 Sep 2016 22:49:57 GMT

@eyeeye you seem to be confusing the ability to change the max MTU with the Data Packet Extension, they are not the same thing. MTU is at the ATT level, Data Packet Extension is at the link level. They are not related to each other directly. You're changing the MTU only, the underlying link level packet will stay the same length, hence you will see exactly the fragmentation and reassembly you are seeing.

RE: S132 v3 Exchange MTU (LE Data Packet Length Extension does't work)

Keton — Sun, 18 Sep 2016 17:15:14 GMT

I've assumed that we are talking about ATT MTU because of diagram you've attached.

Setting BLE_GAP_OPT_EXT_LEN doesn't seem to work but I haven't seen a consumer device with Link Layer packet extension implemented.

I also checked what setting both BLE_GAP_OPT_EXT_LEN and increasing ATT_MTU will do but only thing I've noticed was additional packet fragmentation if BLE_GAP_OPT_EXT_LEN < ATT_MTU+5. It would be interesting to check how nRF52 central + nrf52 peripheral behaves in such configuration but I have only one nRF52 board at home.

If you look at the packet timings you are able to send up to ATT_MTU-3 bytes in single connection interval using write request. Compare this to queued writes where it's only possible to send 1 chunk of data per interval because peer ack is needed.

RE: S132 v3 Exchange MTU (LE Data Packet Length Extension does't work)

eyeye — Sun, 18 Sep 2016 15:54:57 GMT

@Keton, Thanks for your reply! I have successful exchanged the mtu, and the att size is extended.

Only the PDU Length in Link layer didn't extended.

In l2cap layer, the long ATT pdu was fragmented into short Link layer pdu.

That was not the LE Data Packet Length Extension behavior in BLE4.2.

RE: S132 v3 Exchange MTU (LE Data Packet Length Extension does't work)

Keton — Sun, 18 Sep 2016 14:46:08 GMT

If your Nordic device is a peripheral you have to ask central for MTU extension via sd_ble_gattc_exchange_mtu_request.

Be aware that the central device is in complete control of MTU size so it can decline increasing the mtu or can reply with other MTU value.

So maybe iPhone declines mtu extension request? In case of Android not many phones are compatible and it depends both on hardware and ROM version. That's why you need to implement at least barebones MTU exchange as described in S132v3 migration guidelines.

I'd suggest using nRF52-DK with nRFConnect software as a test central device as it supports this feature.

RE: S132 v3 Exchange MTU (LE Data Packet Length Extension does't work)

eyeye — Sun, 18 Sep 2016 11:56:52 GMT

In other word, the LE Data Packet Length Extension does't work.

RE: S132 v3 Exchange MTU (LE Data Packet Length Extension does't work)

eyeye — Sun, 18 Sep 2016 11:14:40 GMT

s132v3 sdk12 with iPhone 6 iOS10