iOS packets per connection interval

RE: iOS packets per connection interval

Ole Bauck — Mon, 14 Dec 2015 14:51:21 GMT

S130/S132 v1 can send/receive 3 packets per connection event as a peripheral, but it only has buffers for 3 packets. A packet is not removed from the buffer before it is ACKed and the last packet is not ACKed before the next connection event. If three packets where sent, one packet from the last connection event will be in the buffer when a new connection event occurs hence there is only place for two more packets. Therefore you can only send two packets per connection event continuously.

EDIT: With S130/S132 v2 you can send 6 packets per connection interval as a peripheral as specified in the release notes (BLE_CONN_BW_HIGH).

RE: iOS packets per connection interval

Ulrich Myhre — Mon, 14 Dec 2015 13:41:31 GMT

Yes, it is assumed that you will be calling sd_ble_tx_packet_count_get(...) to get the number of available buffers. From there it's purely mathematical: Packets_per_CI * bits of data per PDU / connection interval. Packets_per_CI is the minimum of the senders TX buffer count and the receivers RX buffer count. These numbers should also be present in the Softdevice Specification (SDS) under throughput/performance.

RE: iOS packets per connection interval

anasimtiaz — Sun, 13 Dec 2015 20:03:59 GMT

Thanks Ulrich. Where is this information (about buffers) in the S132 documentation? I am struggling to find it. Also, are 2 packets per interval correct then (based on my comment above)?

RE: iOS packets per connection interval

Ulrich Myhre — Sun, 13 Dec 2015 19:23:31 GMT

It depends on the SoftDevice used and the number of links it supports. The S130/S132 has less buffers available per link than the S110 for instance. This is due to RAM constraints on the 16K RAM variants. There are some plans to change the way we do this in the future.

The very latest S130/S132 alpha has an entry in the release notes about the current throughput. It is lower than expected on nRF51, but this will not be present in the production release.

RE: iOS packets per connection interval

anasimtiaz — Sun, 13 Dec 2015 13:17:21 GMT

Thanks RK. Looking in the specs I can see the maximum data throughput is stated as 42.6 kbps for send notification with 7.5ms connection interval. This corresponds to two packets actually (20bytes2packets8bits/7.5ms = 42.67kbps). Am I understanding this correctly?

RE: iOS packets per connection interval

RK — Sun, 13 Dec 2015 11:37:11 GMT

How many TX buffers does the S132 report? The S110 had 6, or possibly 7, and could thus send 6 out per connection interval, and it does (although iOS occasionally seems not to ack the last one and has it sent again the next time). I thought the S132 has fewer TX buffers and hence you can get fewer packets out per connection interval. 2 sounds a bit low however.