Some thoughts on phase coupling in relation to Access Points

[DevonSprings]

Guys,

 

This whole thread was tremendously interesting reading. First of all using an external (to the protocol) wave form like the 60hz zero cross is bound to cause some problems on the network.

 

I am hoping that Insteon thinks to go to a more reliable protocol in I3.

 

What does a protocol need for reliability. Well ethernet, and TCP/IP are great examples. Insteon it seems has made the mistake that repeating commands in an unconfirmed fashion is a way to be as reliable as executing the proper information within the protocol.

 

Transmit StartBits

Transmit Destination

Transmit Command

Transmit CRC

 

On the other end.

 

Listen StartBits

Am I destination ???

Can I perform Command ???

IS CRC Correct ???

Execute Command

 

Transmit Startbits

Transmit Dest

Transmit Ack

Transmit CRC

 

Also the tranmitter needs to listen to what it transmitted and if the CRC does not match understand it probably collided with something else.

 

IF every device is going to repeat the command as some devices might be out of range, the way this is accomplished in the modern world is assigning each device a next hop sequence.

 

I know my neighbors I can hear are?

 

So I listen (notice I listen) and then when that is done I transmit, and then I listen if I colided I wait some random time before I transmit again.

 

I like the idea of Insteon, I just wish it were 100% reliable, and not building in reliability in the protocol, and depending upon the power line timing, but creating its own time.

 

I would think for S3 to work it would have to work on a second frequency with enhanced protocol, and retransmit as long as S1/S2 devices were found.

 

But it would be WAY more reliable than taking the phase of the 60hz as the timing.

 

Inductance and Capicitance both effect phase of the signal.

 

On a 500khz signal for example you could transmit 50kbits per second which is a lot of insteon data, and have it much reliable.

 

Devon

[Brian H]

Devon; Have you had a chance to read some of the Insteon white papers or command data? To see exactly how the Insteon signals are processed.

There are links to a few sites here.

http://www.madreporite.com/insteon/insteon.html

 

The Smarthome Insteon White Paper is slightly dated as it refers to the RF signal being 904 MHz. That was the original SignaLinc RFs frequency. Access Points and all the RF devices are on 915MHz.

[DevonSprings]

Brian,

 

That was interesting information, but my rant is that Ix should be a reliable protocol and at a higher speed so that it has time to better execute the commands.

 

-Devon

[IndyMike]

Brian,

 

That was interesting information, but my rant is that Ix should be a reliable protocol and at a higher speed so that it has time to better execute the commands.

 

-Devon

 

Hello Devon,

 

The subject of this thread was the functioning of the Accespoints. There is lot that I do not understand about these little devices and the decision making process they use for transferring RF onto the powerline.

 

The Accesspoints work very well in many (most?) installations. In others, as Illusion has noted here, the appear to be unable to reliably transmit data onto the opposite phase.

 

I would not call this a failure of the protocol, but rather a difference in the environment. As Illusion noted, after adding a passive coupler, the Insteon protocol worked in his installation.

 

The Insteon implementation is a concession to the medium (powerline) that it uses for communication. This implementation is aimed at maintaining signal to noise ratio (message hopping) and data integrity.

 

Also the tranmitter needs to listen to what it transmitted and if the CRC does not match understand it probably collided with something else.

 

1) Insteon protocol does incorporate embedded CRC's. Devices that decode a bad CRC would presumably not repeat, or respond to the received message.

2) After transmission of a "group message", individual responders are polled to determine whether they correctly received the message.

3) Message retry logic is available if negative acknowledges are received. I am not up to date on the circumstances under which retries are employed.

 

I would think for S3 to work it would have to work on a second frequency with enhanced protocol, and retransmit as long as S1/S2 devices were found.

 

But it would be WAY more reliable than taking the phase of the 60hz as the timing.

 

Inductance and Capicitance both effect phase of the signal.

 

On a 500khz signal for example you could transmit 50kbits per second which is a lot of insteon data, and have it much reliable.

 

The zero crossing is used for a number of reasons.

1) As you noted, it is the "time base" that Intseon devices use for synchronizing their transmissions.

2) Insteon divides the zero crossings after a transmission into "time slots". Message repeaters will only transmit during a predetermined time slot. This synchronization allows multiple devices to retransmit a communication at during a "time slot" to improve the signal to noise ratio.

3) The zero crossing itself is generally the "quiet time" of the 60 Hz cycle. Most noise producing devices will be drawing current during the peaks of the sine wave. Insteon uses this quite time to transmit data in bursts.

 

The 130 Khz carrier is again a concession to the powerline. The powerline can be modeled as a distributed inductance that is terminated into low impedance loads. This forms a voltage divider network which attenuates the transmission. This attenuation increases with frequency.

 

Typical values for the powerline inductance are 0.13 uH/ft. Typical EMC capacitors found in many electronic items are 0.1 uF. Using a 30 foot section of powerline this divider network winds up being:

 

1) 130 Khz - 2.94 ohm series impedance terminated in to 12.2 Ohms; Transfer = 0.8 V/V

2) 500 Khz - 11.3 Ohm series impedance terminated in to 3.18 Ohms; Transfer = 0.22 V/V.