Zigbee Device Object - Discovery vs. Formation

[ming_]

I study on the BeeStack with Zigbee

The ZDO has Network Discovery attempts and Network formation attempts. but I am not clear what is difference between 'discovery' and 'formation'

here is some parameters

Network discovery attempts                    mDefaultValueOfNwkDiscoveryAttempts_c

Network discovery scan attempts               mDefaultValueOfNwkScanAttempts_c

Discovery attempts timeout                    mDefaultValueOfDiscoveryAttemptsTimeOut_c

Network formation attempts                    mDefaultValueOfNwkFormationAttempts_c

Network formation attempts timeout          mDefaultValueOfFormationAttemptsTimeOut_c

[AngelC]

Dear Min,

While network discovery is used to check for the presence of networks within the device’s range, the formation is used by the coordinator to start/form the network. You will find this information in ZigBee specification from ZigBee Alliance. Here are some extracts from such document:

3.2.2.1 NLME-NETWORK-DISCOVERY.request

This primitive allows the next higher layer to request that the NWK layer discover networks currently operating within the personal operating space (POS).

3.2.2.3 NLME-NETWORK-FORMATION.request

This primitive allows the next higher layer to request that the device start a new ZigBee network with itself as the coordinator and subsequently make changes to its superframe configuration.

It is important for any ZigBee developer to read the specification and be familiar with its implementation. I would recommend you to download it form ZigBee Alliance website and check these and other details. It will be very helpful to clarify your doubts.

Regards,

AngelC

[ming_]

Thanks AngelC

Please correct me if I wrong.

The Formation is request(actually create) by coordinator and should do only ones at the first power up.

The Discovery is request by router and end device (coordinator also ??) and should request anytime it requires.

And only coordinator can respond the Discovery request. (is true ??)

Edit:

" Zigbee coordinator node that actually decides when it's time to form a network, from which set of channels,and from which set of PAN IDs." - from 'Zigbee Wireless Networking'

[AngelC]

Dear Min,

The formation request is issued by the coordinator only indeed. A router or end device will not be able to perform this request. Also, your edit about the time of formation of the network is correct. This could be done at any time, whenever necessary.

The discovery request may be sent by any device attempting to discover networks within its range. It is basically translated to an active scan (at MAC level) for available networks in certain channels. This could be sent at any time indeed. Both ZC and ZRs could respond to this discovery mechanism informing the sending node there is a network available.

I would recommend you to read chapter 3.6.1.3 Network Discovery of ZigBee Specification. It contains a detailed description of how networks are discovered to then join the node.

Regards,

AngelC