IEEE Consumer Electronics Magazine - January/February 2024 - 27

constructed by CM d13. In this case, a conflict will
arise between Fog 1, Fog 2, and Fog 3 to update
the blockchain. To handle such a conflict, the
fog node that calculates the nonce before any
other fog node would first broadcast the block
to others and would be considered as the final
version of the block. The hash or the digest of
the previous block is mainly used to establish
the connection among the sequence of the
blocks/events.
The fog node does not just directly add the
newly received block to the existing chain, rather it
processes and analyzes the block beforehand. The
fog node first verifies if the block is from an authorized
CM. For this, fog node checks the cluster identifiers,
collector/reactor identifier, and previous
block's digest. The other condition that needs to
be verified is that if the data payload is from a reactor,
the collected data in the received data payload
should match the value of Event field of previous
block, if the previous block is from a collector.
It is possible for any fog node to receive multiple
consecutive data payloads from the same
CM. In other words, the collector/reactor identifier
of newly received data payload is same as
that in the most recent block in the blockchain.
If the CM is a collector, the fog node simply
extracts the value of event data field from the
newly received data payload and append that
value to the event data field of the most recent
block in the blockchain. However, if the CM is a
reactor, the values of the collected data and event
data field of the new data payload are extracted
and appended to the respective data fields of
most recent block in the blockchain. Following
the append operation, the nonce would be recalculated
by the same fog node. Once this process
is done, the newly received data payload is simply
discarded and the updated blockchain is broadcast
to the other fog nodes in the network.
Operation Flow
This section presents the detailed end-to-end
flow, as shown in Figure 5, including the generation
of data payload at the edge, forming the
blockchain at fog, all network operations, and
communications among all the entities. In the
previous sections, the construction mechanism
of data payload and blockchain by CM and fog
are illustrated, respectively.
January/February 2024
FIGURE 5. Journey of a data payload, blocks, and
blockchain.
The entire process, as in Figure 5, starts when
there is an event in the environment or a change
in the state of the environment. The event can
be based on the time. Such an event triggers the
collectors that continuously monitor the state of
the environment (Step 1). Based on the event
the corresponding collectors collect the environmental
data and constructs the data payload
with a set of other metadata, as discussed in the
" Construction of Data Payload by CMs at the
Edge " section (Step 2). For instance, if the outside
luminosity level changes, the corresponding
collector would be a light detector. If a person
crosses a certain area, the motion detector
would be triggered. The constructed data payload
will then be broadcast to the other CMs and
the nearby fog nodes (Step 3). After receiving a
new data payload from other CMs, a collector or
reactor would extract the data payload's event
data and accordingly either react to the environment
or further collect the environmental data
based on the predefined task.
On the other hand, upon receiving the same
data payload, the nearby fog nodes either
update the most recent block present in existing
blockchain (Step 5.1, if the newly received data
payload is from the same CM) or add a new
block to the existing blockchain (Step 5.2, if the
newly received data payload is from a different
CM), depending on the source of the data payload.
At this stage, all the fog nodes that receive
the data payload will compete for finding the
required nonce. Once this process is done, the
updated blockchain will be further broadcasted
to other fog nodes in the network (Steps 6.1 and
6.2). This way, all the fog nodes will have a list of
updated blockchains.
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IEEE Consumer Electronics Magazine - January/February 2024

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