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Re: [ipwave] traffic lights status displayed in the car, and the latency problem

Alexandre Petrescu <alexandre.petrescu@gmail.com> Wed, 04 September 2019 13:56 UTC

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From: Alexandre Petrescu <alexandre.petrescu@gmail.com>
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Date: Wed, 04 Sep 2019 15:56:21 +0200
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Subject: Re: [ipwave] traffic lights status displayed in the car, and the latency problem
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Le 04/09/2019 à 15:42, Alexandre Petrescu a écrit :
> [...]
>> The 802.11 OCB was never intended to communicate with the traffic 
>> controller, the RSE is.
>
> Well, RSE is the Road-Side Entity, right?
>
> The implementations that I know and that run on RSE do indeed query the
> traffic lights controller (tlc) using a protocol specific for tlc.  It
> is DIASER in France; they run DIASER on Ethernet cable.  These RSE
> implementations obtain the status data from tlc and then put it in the
> SPAT-EM message.  It is this SPAT-EM message that is put on OCB wireless
> towards the cars.
>
> However, that DIASER query is a periodic query: it is once every second
> or so (1 Hz).  One can go higher than one second, but it risks
> overloading the computation capability of the tlc.  We have performed
> measures and came up with 1 Hz being very good, but 2 Hz overloading the
> tlc.


I put up a report with the numbers we found

https://www.researchgate.net/profile/Alexandre_Petrescu/publication/335608641_Rapport_experimentation_interrogation_des_controleurs_de_feux_Lacroix_et_Aximum_Le_but_c'est_d'identifier_a_quel_taux_frequence_on_peut_les_interroger_en_DIASER_pendant_long_temps_sans_qu'il_ne_cessen/data/5d6fc1fa299bf1cb8086ce23/Rapport-experimentation.pptx

Alex

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