Embedded Rule-based Management for Content-based DTNs - Advances in Network-Embedded Management and Applications - page 90

NOTIFICATION
notification_id=notif123
source=sensor_node1
message_type=trap
watcher_id=watch_temp
mib=temperature
value=36.5
END

SUBSCRIBE
subscription_id=sid123
subscriptor_id=collector1
FILTER
mib=temperature
value > 35
END

(a) A Notication. (b) A Subscription.

Fig. 2. The Messages of the Notication Bus

2.1 RON Protocol

In our network, there are two entities: subscriptions and notications. The associ-
ated messages are plain text multi-line strings.
Notication messages are the mean of distributing information in the network.
A sample notication is shown in Figure 2(a) . As seen, it is a simple list of key/value
pairs. The only mandatory attribute is notication id, a unique identier. The user
of the bus must dene additional elds and their semantics. In the example we
can see a source eld (the identier of the sensor node), and the remaining elds
describe the sensor-reading being carried (36.5 from a temperature sensor).
A Subscription message signals the interest of its creating client on receiving
certain notications. A typical Subscription is shown in Figure 2(b) . The subscrip-
tion is composed of two parts, the header and the lter. The header contains general
information, like a unique Subscription identier and the identier of the node sub-
scribing. The lter species a set of conditions, which must be met by a notication
for it to be delivered to the client. Each condition is of the form attribute-operator-
value, where attribute is a Notication eld. If a Notication does not contain that
eld, the given expression is considered satised. In other words, a Notication fails
a lter only if it contains a eld which fails some condition. In the example, the
subscription will match any notication with a payload of a temperature over 35
(whatever sensor node originates it).
To move those entities trough the network, each node maintains S j , a table
of accessible destination (Subscriptions in our case) with an associated quality for
each. The quality of a destination represents how good is the node to reach that
destination. Nodes periodically exchange their destination lists with their associated
qualities, and update their own qualities in the process. Also, the nodes keep a set of
messages N j . The amount of messages that can be carried is limited, so a decision
must be made on what message to carry. The destination quality information is
used to select which messages are best carried by the node, which are the messages
targeted at destination with higher qualities.
As usual for a gossiping algorithm, RON can be split in two threads: an active
emitting main loop (the Control Cycle), and a passive event handler (the Message
Handler) that receives, processes and issue messages.