Packet number in one connection interval with 2M phy

[helen]

Hi Nordic，

One of my customer has a problem about 2M phy.

They use 52840 connected with IOS via 2M phy.

They set MIN_CONN_INTERVAL and MAX_CONN_INTERVAL both to 20, which mean 25ms connection interval.

The ATT MTU is 247.

When they set NRF_SDH_BLE_GAP_EVENT_LENGTH to 6(7.5ms), they found there is only on packet in one connection interval.

When they set NRF_SDH_BLE_GAP_EVENT_LENGTH to 20, they found there is only 5 packets in one connection interval.

in theory, transmit one packet of 251 bytes need less than 2ms by 2M phy.

for gap event and connection interval 25ms, there should be 12 packets in one interval, but there is only 5.

What am I lost when calculate it?

thanks.

[Simonr]

Hi

Unfortunately, doing large BLE transmissions using iOS is not trivial unfortunately. Most phones support the 247 byte MTU, but iOS only supports up to 185 bytes of MTU as far as I know, so there might be an issue there (discussed and described in detail here). What iOS device and version are they running here? 

You can also ask the customer to check out this blog post which has a good description on how they were able to achieve the maximum possible throughput on nRF52840 devices.

Best regards,

Simon

[helen]

Hi

The customer use iphone8 plus ,iOS15.3 .

I think you may misunderstand the question, the customer's doubt is about the maxinum number of packets in one connect interval, not MTU. 

Helen.