CC1352P7: Wi-SUN connection time and optimization

Hi Karthik,

Wi-SUN is a mesh IOT network that usually consists of line powered routers and gateways. A good overview of the stack capabilities is our Wi-SUN Stack User's Guide: https://dev.ti.com/tirex/explore/content/simplelink_cc13xx_cc26xx_sdk_8_30_01_01/docs/ti_wisunfan/html/wisun-guide/wisun-index.html# 

1. The time that it takes to connect a router to a gateway is a matter of minutes because all devices in a Wi-SUN network are frequency hopping. That means when a new router wants to join the network it needs to first send a PAN advertisement solicit message that needs to be received by the border router and answered with a PAN advertisement message. After this the router has the frequency hopping information of the gateway and the join process transitions to state two were the certificates are exchanged which takes time due to the size of the certificate and the PHY that you chose. You can find the details of the join process here: https://dev.ti.com/tirex/explore/content/simplelink_cc13xx_cc26xx_sdk_8_30_01_01/docs/ti_wisunfan/html/wisun-stack/join_process.html# 

If you are using our latest SDK 8.30.1.1 https://www.ti.com/tool/download/SIMPLELINK-LOWPOWER-F2-SDK/8.30.01.01 a realistic expectation is below 15 min for 100 nodes.

2. The fastest join time you will achieve by using the network profile Maximize Responsiveness (https://dev.ti.com/tirex/explore/content/simplelink_cc13xx_cc26xx_sdk_8_30_01_01/docs/ti_wisunfan/html/wisun-stack/wisun-stack-overview.html#network-profiles) and using the rapid join option (both selectable in SysConfig). This will result in the time stated above.

3. The maximum range depends mainly on the TX output power of the device, the PHY that you chose and the mounting height of the devices. You can use our range estimator to estimate this for your use case: https://www.ti.com/tool/RF-RANGE-ESTIMATOR You need to consider this as point to point range because Wi-SUN is a mesh network which means routers can connect to the gateway over other routers (basically each router is a repeater for other routers).

4. If you are looking instead for a low power start network for battery powered nodes please have a look at the TI 15.4-Stack: https://dev.ti.com/tirex/explore/content/simplelink_cc13xx_cc26xx_sdk_8_30_01_01/docs/ti154stack/html/ti154stack-guide/ti154stack-index-cc13xx_cc26xx.html# which allows for frequency hopping and sleepy nodes.

Please let me know if you have more questions after looking through the documentation.

Kind regards,
Theo

Hi Karthik,

if the devices are line powered I strongly recommend you to use Wi-SUN.
The protocol is made exactly for such use cases. 

After the initial join process the Wi-SUN network will be always up and the nodes maintain their connection to the gateway and each other automatically. Also the nodes are automatically re-routing to always chose the cheapest connection to the gateway. This means you have no overhead for handling the mesh behavior because it is done automatically by the stack. From the gateway you can access each device in the network by it's IPv6 address which makes the integration with a cloud application and host management easy. You can send unicast and multicast messages and we integrate the CoAP protocol. All routers subscribe by default to one multicast group so that you also have a broadcast functionality that can be used to trigger all devices with low latency for safety critical shutdown mechanisms.

If you really want to force a star network you can do it with Wi-SUN as well. The option is provided in SysConfig and it will lead to all routers connecting to the border router directly (no mesh). But then you are limited to the point to point range depending on the parameters explained in my first message and can not use the mesh to extend the range.

We also provide a Linux host application that connects to the Border Router over  USB uart. https://github.com/TexasInstruments/ti-wisunfantund 
On the Linux side you interact with the network as network socket and the application forwards traffic. It also already supports an external DHCP and external authentication server if you want to use it so that the network is managed completely on the host. You will also find the default web application that shows you your network setup after you started it.

You can have a look at our setup examples to get started. The examples use our simpler host application but in your case I strongly recommend you to use the linux host application as it will ease your development. https://dev.ti.com/tirex/explore/node?node=A__ADa2uuCmB8bxyc-jInEdoQ__com.ti.SIMPLELINK_ACADEMY_CC13XX_CC26XX_SDK__AfkT0vQ__LATEST 

Kind regards,
Theo

Hi Karthik,

thank you for providing me with more background information. 

Here we need to differentiate between join and re-join looking at Wi-SUN. The initial join process only happens when the device joins the network for the first time, you can see it as a initial setup. If you would start a network with 1 border router and 100 routers all at the same time it would take less 10 to 15 minutes until all devices are connected due to the required security exchange. This is obviously also faster if you have already a network set-up and want to only connect one more device to it. 

Now looking at the situation that you are concerned about. If a device joined the network it gets provided with an address provided by the DHCP server (either running on the border router or the host) and a it has a network key. Both of this has an expiration time that can be configured at which it will get re-newed automatically. If a device is now disconnected for any reason and needs to reconnect we are in a re-join situation where the device does not need to go through the security exchange again because it has still a valid key. You can expect the router to re-join the network in around 1 min.

I'm sure that you need to implement anyways some kind of additional handling for the case that the device disconnects. But in general you will end up with a very reliable network after join because the network maintains itself and you are not in an environment with a lot of obstructions or noise. Also the Wi-SUN Stack is frequency hopping in a pseudo random pattern which means that the connection will not be lost if there is one frequency covered as most likely the next one in the hopping sequence will be free again. This means the stack is very resilient and a disconnection would most likely only occur if the router looses power connection and I guess this would mean that also the connected motor lost power connection.

If you are looking for a more lower level stack I think you can checkout the TI 15.4-Stack and of course it would also be possible for you to develop your own proprietary protocol using our radio Apis.

Do you already have the CC1352P7 LaunchPads?

Kind regards,
Theo

Hi Karthik,

if you have the kits you can setup easy tests with the out of the box examples to get familiar with the network functionality. Please reach out once you have them and need help to set up a test. A good starting point is the SimpleLink Academy: https://dev.ti.com/tirex/explore/node?node=A__ADa2uuCmB8bxyc-jInEdoQ__com.ti.SIMPLELINK_ACADEMY_CC13XX_CC26XX_SDK__AfkT0vQ__LATEST 

What I meant is that no matter which wireless protocol you use you need to always implement the handling of a connection loss. I explained in my last post how the MCU will behave from a Wi-SUN stack point of view. Since you mentioned that it will be connected to a motor I would expect that there is some kind of backup implemented that will safely turn off the motor if the connection is lost for a defined timeout.

We have two host applications for Wi-SUN and both connect to the MCU over UART. The first one is TI Wi-SUN FAN Spinel https://github.com/TexasInstruments/ti-wisunfan-pyspinel and the second one is the linux host application 
ti-wisunfantund https://github.com/TexasInstruments/ti-wisunfantund. Both are documented in their git repositories and you can go through the list of commands and features that they provide.

If you run debian on the Raspberry Pi you can run both host applications out of the box and connect the MCU over UART. There is nothing that needs to be done additionally.

You can estimate the range using the https://www.ti.com/tool/RF-RANGE-ESTIMATOR. You can select the different Wi-SUN PHYs and also see the influence of antenna mounting height and tx power (need to take into account the local regulations). This is always giving you the point to point range.

Kind regards,
Theo