Recommended configuration for data length extension + multiple connections

RE: Recommended configuration for data length extension + multiple connections

Petter Myhre — Wed, 11 Oct 2017 15:54:22 GMT

When the connection event is over it is over, if you have set a larger event length than connection length it will be as you have set the event length equal to the connection length.

RE: Recommended configuration for data length extension + multiple connections

Youssif — Wed, 11 Oct 2017 13:50:08 GMT

What happens when the connection interval is less than the connection event length?

For example, if we set the connection event length to 15ms, then have a connection and set the connection interval to 7.5ms, what is the number of 27 byte packets that will get through per connection interval?

RE: Recommended configuration for data length extension + multiple connections

Petter Myhre — Mon, 18 Sep 2017 14:20:40 GMT

Looks correct.

RE: Recommended configuration for data length extension + multiple connections

Youssif — Fri, 15 Sep 2017 13:26:55 GMT

OK thanks, I think this is becoming clearer. However I'm not sure I fully understand the formula so can you please check if my math is correct:-

For 1 packet (size = 27) per conn interval, the event length = 1.25 + ((27-27)*8*2*(1))/1000>  = 1.25ms
For 3 packets (size = 27) per conn interval, the event length = 3.75 + ((27-27)*8*2*> (3))/1000 = 3.75ms
For 6 packets (size= 27) per conn interval the event length = 7.5 + ((2> 7-27)*8*2*(6))/1000 = 7.5ms 
For 1 packet (size = 251) per conn interval, the event length = 1.25 + ((251-27)*8*2*(1))/1000 = 4.834ms
For 3 packets (size= 251) per conn interval, the event length>  = 3.75 + ((251-27)*8*2*(3))/1000 = 14.5ms 
For 6 packets (size= 251) per conn interval, the event length = 7.5 + ((251-27)*8*2*(6))/1000 = 29ms

So roughly the values are 1, 3, 6, 4, 12, and 24 (respectively), in 1.25ms units. Is this correct?

RE: Recommended configuration for data length extension + multiple connections

Petter Myhre — Fri, 15 Sep 2017 10:12:50 GMT

Yes. They are in us range. And now you have to set the event length units of 1.25 ms. The minimum event length is 2 (2500 us). So that would be be closest to low bandwidth. 3 (3750 us) would be closest to medium bandwidth. 5 (6250 us) or 6 (8750 us) would be closest to high bandwidth.

You other point seems to be answered by this paragraph in the Suggested intervals and windows section in the S132 v5 SDS:

When long Link Layer Data Channel PDUs are in use, it is recommended to increase the event length of a connection. For example, Link Layer Data Channel PDUs are by default 27 bytes in size. With an event length of 3.75 ms, it is possible to send three full sized packet pairs on LE 1M PHY in one connection event. Therefore, when increasing the Link Layer Data Channel PDU size to 251 bytes, the event length should be increased to 15 ms. To calculate how much time should be added (in ms), use the following formula: ((size - 27) * 8 * 2 * pairs) / 1000.

RE: Recommended configuration for data length extension + multiple connections

Youssif — Thu, 14 Sep 2017 14:21:21 GMT

Can you please explain why that is? The values in Table 25 are in the us range, therefore 1.75, 3.7, and 6.56 ms. So in 1.25 ms units, this is equivalent to 1.4, 2.96, and 5.25. Is that correct?

Another point, in softdevice v3.0.0, setting the BW to LOW, MID, and HIGH is the equivalent of sending 1, 3, and 6 packets per connection interval. For throughput testing, this allowed us to change the BW to 6 when testing against Android, and 3 when testing against iOS (even though iOS supports 4 packets per interval). How is this replicated with the event length parameter (with a packet length of 27 and a packet length of 251)?

RE: Recommended configuration for data length extension + multiple connections

Petter Myhre — Thu, 14 Sep 2017 13:42:29 GMT

You set the event length to 1, 3 and 6? You should set it to 1750, 3700 and 6560 (in 1.25 ms units).

RE: Recommended configuration for data length extension + multiple connections

Youssif — Wed, 13 Sep 2017 12:53:31 GMT

More importantly, reverting to the scenario of having 1 connection only, and with event length extension disabled, what should I set the event length to in order to replicate the LOW, MID, and HIGH BW in sd v3.0.0? I tried 1, 3, and 6 (respectively) - which also happens to be the equivalent to tEEO values - but the throughput values were well below what we were seeing with sdv3.0.0. It's as if for packet lengths of 251, the LOW, MID, and HIGH values are different than for packet lengths of 27 bytes. Any thoughts?

RE: Recommended configuration for data length extension + multiple connections

Youssif — Wed, 13 Sep 2017 12:52:57 GMT

Unfortunately this is still fuzzy to me. What I understood from the links and documentation is that for sd3.0.0, the low, mid, and high BW were 1, 3, and 6 (and this is equivalent to the number of 27-byte packets that could be sent). This means for HIGH BW we could get 6 packets through. However, changing the packet length to 251 still meant that 6 packets could be sent through, given that the connection interval was increased. This isn't the case for the current version of the softdevice.

RE: Recommended configuration for data length extension + multiple connections

Petter Myhre — Tue, 12 Sep 2017 06:34:36 GMT

It should be around the values for tEEO in Table 25 in S132 SDS .

RE: Recommended configuration for data length extension + multiple connections

Youssif — Mon, 11 Sep 2017 13:27:38 GMT

Thanks for the link. So without taking connection event extension into consideration, what was the exact allocation in softdevice v3.0.0 (For low, medium, and high bandwidth configuration) in terms of event length?

RE: Recommended configuration for data length extension + multiple connections

Petter Myhre — Wed, 06 Sep 2017 11:18:38 GMT

Not really dynamically with v3.0.0. The amount of time allocated depended on the bandwidth configuration. And then you had connection event extension that kicked in if there was more time.
The event length specifies the length reserved for a connection event, the connection interval specifies the maximum event length.
Have you seen this? With 8 central connections with a connection interval of 400 ms on each, and even distribution of "throughput". I would set the event length to around 50 ms, but this has to be tuned. 400 ms event length and 400 ms connection interval should only be used if you have 1 connection, because then you are giving all radio time to one connection.