<p>It looks like it is actually periods of 336 blocks instead of a rolling window. It is like what BIP 9 specifies, but uses 336 blocks as the window and 269 blocks as the threshold. The windows begin when a block's height is a multiple of 336.</p>

CC BY-SA 3.0
2017-07-19T13:49:31.730Z
Is there any particular reason why it is implemented in this way instead of rolling fashion?
sanket1729
CC BY-SA 3.0
2017-07-19T16:19:50.723Z
Yes, this is inherited from BIP9. The reasons there are to be more conservative (there is randomness involved, if you give every block a chance to activate, each of those increases the probability that it activates when in reality the threshold is not reached), giving people less sleepless nights (knowing in advance when something can activate is much nicer than having to check at every block), and to make the behaviour more analysable (each attempt now is a statistically independent sample).
Pieter Wuille
CC BY-SA 3.0
2017-07-18T18:19:08.873Z
2017-07-18T18:19:08.873Z
Ava Chow
<p>I understand that BIP91 needs 269/336 signaled blocks.<br>
My question is is it a rolling window of any 336 blocks or are there activation periods of 336 blocks that start and end at predetermined block numbers?</p>

<segregated-witness><segwit2x><bip91>
BIP91 Activation Period
Albert S
# BIP91 Activation Period

(Asked by: username_0 on 2017-07-18)

I understand that BIP91 needs 269/336 signaled blocks.  
My question is is it a rolling window of any 336 blocks or are there activation periods of 336 blocks that start and end at predetermined block numbers?

**Tags:** segregated-witness, segwit2x, bip91


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## 1 answers

### Answer by username_1 on 2017-07-18. Score: 4

It looks like it is actually periods of 336 blocks instead of a rolling window. It is like what BIP 9 specifies, but uses 336 blocks as the window and 269 blocks as the threshold. The windows begin when a block's height is a multiple of 336.

> **Comments:**
> **username_2**: Is there any particular reason why it is implemented in this way instead of rolling fashion?  
> **username_3**: Yes, this is inherited from BIP9. The reasons there are to be more conservative (there is randomness involved, if you give every block a chance to activate, each of those increases the probability that it activates when in reality the threshold is not reached), giving people less sleepless nights (knowing in advance when something can activate is much nicer than having to check at every block), and to make the behaviour more analysable (each attempt now is a statistically independent sample).  

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