# Why is there a factor 2 when calculating the knownRouteUnicastTime

**URL:** <https://forums.digi.com/t/why-is-there-a-factor-2-when-calculating-the-knownrouteunicasttime/20361>\
**Category:** XBee & XBee Gateway\
**Tags:** xbee-api-mode\
**Created:** [March 20, 2019, 7:55am UTC](https://forums.digi.com/t/why-is-there-a-factor-2-when-calculating-the-knownrouteunicasttime/20361 "2019-03-20T07:55:48Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![johanneslucke](https://avatars.discourse-cdn.com/v4/letter/j/ee59a6/32.png) [@johanneslucke](https://forums.digi.com/u/johanneslucke)\
**Post date:** [March 20, 2019, 7:55am UTC](https://forums.digi.com/t/why-is-there-a-factor-2-when-calculating-the-knownrouteunicasttime/20361/1 "2019-03-20T07:55:48Z")

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In the XBee 868 SX user manual the formula for the following formula is given to calculate the timeout between two unicast transmission on a known route:  
knownRouteUnicastTime=2_NH_MR\*unicastOneHopTime  
Why is there a factor 2 included? Is it because of the acknowledgements which are sent back? However I had the feeling that the acknowledgments where already taken into account in the unicastOneHopTime parameter