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CC2650 6LoWPAN Questions

Glenn Vassallo
Guru 21435 points
Other Parts Discussed in Thread: CC2650, CC2538

I am researching the use of the CC2650 6LoWPAN in a sensor network solution and had a few questions.

1. What is the maximum number of nodes that each mesh network can support...would 1500 be possible? What are the recommendations?

2. What is the maximum number of nodes that each edge router can support...again is 1500 possible?

3. Will the nodes still be able to run on batteries for extended periods? Each node will have 1 simple sensor and likely update rate of around 1 sample a minute maximum...perhaps less.

4. Can 6LoWPAN work with more than 1 edge router...so you have some form of redundancy?

5. Are there any 6LoWPAN (over 2.4GHz) to Wi-Fi Edge Router available on the market? or is their any software or reference designs available for this?

Thanks, any questions that can be answered would be of a great help! 

Glenn.

  • 0
    TI__Genius 16570 points
    Hi Glenn,
    lots of interesting questions. Let me first send you the link of our 6LoWPAN wikipage which we recently have been updating after we launched the new CC26xx ULP platform: www.ti.com/contiki-6lowpan-wiki

    1) the answer to this question depends on several factors: the application layers, the traffic profile on top of the 6LoWPAN stack, the physical topology and the resources available on the device. The more lenient the protocols are on top of IP, the bigger the network can be. On the other side the bulkier the protocols are (like XML on HTTP transactions), then the more complicated it is to handle intense traffic profile on the network. In terms of over the air utilization, the most efficient combination in terms of over the air resource utilization is CoAP over UDP. Then as mentioned it depends on how much data you exchange and how frequently. Typical deployment can go beyond hundreds of node in the network. 1500 in a single deployment looks a bit of a stretch
    2) Edge routers are typically the devices with the biggest requirements in terms of resources. It depends how an edge router is implemented (ie an embedded host vs a Linux processor). Again the number of 1500 seems a bit of a stretch in a single network
    3) yes especially combined with the best in class performance of 26xx, this is possible

    4) Contiki multiple BR is in the works. github.com/.../Multiple-6LBR . I suggest you check this out and ask the Contiki community

    5) Yes there are 2.4 Ghz Wi-Fi/6LoWPAN device which can act as an embedded border router. On the Conitki repository tree you can find an example of an Eth-6LoWPAN border router based on CC2538: github.com/.../CC2538DK-Software-Configuration

    Thanks,
    TheDarkSide
  • 0 in reply to TheDarkSide
    Guru 21435 points
    Hi TheDarkSide,

    Thanks for your detailed and excellent responses, I will look into all the resources you have provided.

    This will be a very innovative IoT solution, and a really good demonstration of the CC2650 using 6LoWPAN. Being able to develop prototypes with the new SensorTag for this really makes it a great option, I am just waiting on more DevKits for the SensorTag to arrive!

    Not many people are aware of the advantages of 6LoWPAN, and the reduction product development efforts when you can directly connect to the Cloud instead of having to develop a Gateway. So very interested in commercially available edge router solutions, preferably ones that can just be purchased and used like you use a Wi-Fi Router. If I could find one of these, I am pretty sure this would convince the customer to move forward with my proposal.

    The solution is likely to use JSON over HTTP, will this effect battery longevity very much or will it just effect the maximum number of nodes for each 6LoWPAN network?

    Glenn.
  • 0 in reply to Glenn Vassallo
    TI__Genius 12480 points
    Hi Glenn,

    First some answers and additions to the original post:

    2) Each route entry in the Contiki Edge Router consumes 82 bytes, form that perspective there is not problems supporting 1000 devices on a Edge Router runnin on a Linux platform. The problem lies in the application and network and the total available bandwitdh.

    5) It should be straight forward to replace the ethernet interface with wi-fi on the 6LBR running Edge Router. People has done it before, see this wiki: github.com/.../9

    I would not recommend HTTP/TCP on a network this size, main reasons are that you risk long TCP backoff periods when collisions, TCP headers are big (20 bytes) and not compressed in the 6LoWPAN layer (as UDP header is). COAP and UDP is much more efficent.

    Best,
    Jonas
  • 0 in reply to Firefighter
    Guru 21435 points

    Hi Jonas,

    Thanks for the additional information....I do have a few other question regarding the architecture.

    The proposed solution will be communicating directly to the Azure Cloud using REST API (i.e. HTTP/JSON) or preferably AMQP (smaller binary application layer protocol), so I will have to use TCP.

    1) When you say, network of this size, were you referring to the 1000 nodes per Edge Router option? As adding extra Edge Routers will not be a big issue if they are required to support the desired features.

    2) There may be the need to send commands to each node individually using a publisher/subscriber pattern. This requires opening a connection from embedded device (node) to the cloud and leaving it open so that it can send and receive data/commands. Do you have any comment on what impact this will have on the solution, for example the number of Edge Routers required and also Battery consumption?

    Glenn.

  • 0 in reply to Glenn Vassallo
    TI__Genius 12480 points
    Hi Glenn,

    Sorry about the delay...

    I understand, I guess that you have taken a look at the MQTT demo included in:

    github.com/.../cc26xx-web-demo
    and
    github.com/.../mqtt-demo

    Those are using MQTT over TCP, so very similar as your setup.

    1) Yes, I was refering to the number of devices each Edge Router can handle.

    2) In Contiki UIP_CONF_MAX_CONNECTIONS defines the maximum number of active TCP connections. I do not know how much memory each of those reserves, but this needs to be looked into for the edge router in order to determine the number of routers needed. Regarding the power consumption I am not certain how much it will be affected by the TCP control traffic, this needs to be examined in detail.

    I hope this gives some ideas for your implementation!

    /Jonas
  • 0 in reply to Firefighter
    Guru 21435 points
    Thanks Jonas,

    Yes, this gives me a better idea on things....it looks like AMQP over TCP will be the better option (just need to squeeze this in some how...due to large library)....and a larger battery, not a coin cell. And a lot of testing :-)

    Unfortunately the Edge Router (BR) situation does not seem simple at the moment, the one company that did have a commercial level solution has sold out on their website and have not responded to emails, they look like they are focusing on complete solutions now. There is an opportunity from someone to build and sell these things, as it is a lot easy to convince a client to go with a particular solution when I can tell them that some of the parts can be purchased off the shelf...this way they can focus on getting the data and application right for their market....as most customers I am talking to are wanting to sell a Cloud service and not devices.

    Glenn.
  • 0 in reply to Glenn Vassallo
    TI__Genius 12480 points
    Agree on the Edge Router situation... There are, as I see it, two options:

    1) Low cost embedded Edge Router, basically handling the conversion between Ethernet/Wi-Fi and IEEE802.15.4 (at least on our case)
    2) High performance Linux based Edge Router.

    Option 1 is truly low cost, as it can be implemented in e.g. CC2538 and a simple Ethernet PHY/MAC transceiver. I know there are commercially available platforms being developed at the moment. Send me a PM if this is of interest and I can put you in contact with the right people.

    Option 2 is very attractive, since as time goes, 6lowpan/ieee802.15.4 support will be added to the Linux kernel, making it easy to add an ieee802.15.4 interface to a standard linux router.

    /Jonas
  • 0 in reply to Firefighter
    Prodigy 10 points

    HI,

     I'm looking for an Edge router. Any pointer is appreciated.

     AH