[ZWay JS API] each Set() triggering a corresponding Get ?

[Bids]

Hi,

I am experimenting with the JS API, and I noticed in the logs that when I perform an action like:

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zway.devices[9].instances[0].SwitchBinary.Set(0);

I properly see the z-wave frame being sent to set value to 0 on the switch node,

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[2014-11-02 22:07:00.519] Job 0x13 (SwitchBinary Set): Delivered
[2014-11-02 22:07:00.519] SETDATA devices.9.data.lastPacketInfo.delivered = True
[2014-11-02 22:07:00.519] SETDATA devices.9.data.lastPacketInfo.packetLength = 6 (0x00000006)
[2014-11-02 22:07:00.520] SETDATA devices.9.data.lastPacketInfo.deliveryTime = 78 (0x0000004e)
[2014-11-02 22:07:00.520] SETDATA devices.9.data.lastPacketInfo = **********
[2014-11-02 22:07:00.520] SendData Response with callback 0x46 received: received by recipient
[2014-11-02 22:07:00.520] SETDATA devices.9.data.lastSend = 1323420 (0x0014319c)
[2014-11-02 22:07:00.520] Job 0x13 (SwitchBinary Set): success
[2014-11-02 22:07:00.520] Removing job: SwitchBinary Set

But for this same unique Set() call, there is also systematically a corresponding "Get" being performed by the Z-way server immediately after:

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[2014-11-02 22:07:00.698] Job 0x13 (SwitchBinary Get): Delivered
[2014-11-02 22:07:00.698] SETDATA devices.9.data.lastPacketInfo.delivered = True
[2014-11-02 22:07:00.698] SETDATA devices.9.data.lastPacketInfo.packetLength = 5 (0x00000005)
[2014-11-02 22:07:00.698] SETDATA devices.9.data.lastPacketInfo.deliveryTime = 55 (0x00000037)
[2014-11-02 22:07:00.698] SETDATA devices.9.data.lastPacketInfo = **********
[2014-11-02 22:07:00.699] SendData Response with callback 0x49 received: received by recipient
[2014-11-02 22:07:00.699] SETDATA devices.9.data.lastSend = 1323435 (0x001431ab)
[2014-11-02 22:07:00.699] Job 0x13 (SwitchBinary Get): success
[2014-11-02 22:07:00.699] Removing job: SwitchBinary Get

Is this done on purpose ? Since every (non-broadcast) Z-wave frame is acknowlegded, I don't see the need for reading values immediately after setting them on the node, especially since it doubles the traffic on the network.
Can anyone shed some light on this ?

Thanks !

[pofs]

Yes, this is done on purpose.

1) It might be not necessary for you, but for automation scenarios it might be important to have actual value as soon as possible.
2) For sleeping battery devices packet can only be delivered when device wakes up. When you really need a value, waiting for wakeup would take much more time than issuing Get request immediately with Set (so both packets are dispatched during the same wakeup cycle).
3) You don't really use that much Sets daily to actually double traffic on your network. It just increases a little bit. Even more, devices supporting multi-command will receive both Set and Get as a single packet (with just one acknowledgement).
4) If you're making multiple Set calls in a short period of time (or, in case of battery device, before device wakes up), only one Get will be requested in the end to avoid unnecessary traffic.

You may consider it as a trade-off between a little extra traffic and keeping device data in consistent state.

[Bids]

Pretty clear explanation, thank you.
In my case, my primary concern is the latency introduced by the additional Get calls : when setting a specific value on 20+ devices upon receiving a given trigger (scene activation in my case), all these request queue up and end-up representing a significant time between the Set on the first device and the set on the last device.
Is this behaviour specific to the JS API, or does it also apply to the lower level zDev API ?

Regards,