Embedded Rule-based Management for Content-based DTNs - Advances in Network-Embedded Management and Applications - page 91

The Control Cycle periodically triggers two actions. The rst is the broadcasting
of a Views message. This message contains a list of all subscriptions in S j and their
associated quality. The receivers of this node will use that data to maintain their
own subscription qualities and trigger Notication broadcasts. The second Control
Cycle's action is to periodically decrease the quality for all subscriptions (the aging
process).
The Message Handler listens the network and can receive two types of messages:
{ Views message. These messages come from other node's Control Cycle. Upon
reception, for each subscription in S j that also appears in in the View mes-
sage, the algorithm will increase its quality. Furthermore, it will iterate trough
all notications in N j , and for each that matches a recevied subscription will
broadcast a Notication message.
{ Notication message. Notications proceed from the Message Handler of other
nodes. While N j is not full, all notications are stored. When N j becomes full,
the algorithm will look for a Notication with a smaller accumulated quality Q
to replace. The accumulated quality Q for a notication is implemented as the
sum of all subscription qualities that the given notication matches.
To keep the broadcasts reduced to a minimum, special care is taken. In rst
place, when Views message are broadcast, only the subscription's identiers and
associated qualities are transmitted. If a node sees the identier of a subscription
it does not have, it requests it in a separated message. Second, nodes timestamp
entries in N j and S j as they listen the medium, and will refrain from transmitting
data already seen inside a (congurable) time frame. Thus, when a Views broadcast
triggers a Notication message broadcast from one node, this message will reach
other nodes in the network and will inhibit them from repeating it. To this purpose
and to avoid synchronization problems every sending is delayed by a small random
time.
When broadcasting a Views message, there is a chance other nodes will answer
with notications already carried. To reduce this chance, a bloom lter of carried
notications could be included in said Views message. This way, receiving nodes
could easily check if a notication is a repeat and skip it. For an in-depth description
of the RON algorithm, see [10].
3 Managing a Delay Tolerant Protocol
There are several parameters that have a signicant inuence on protocol's perfor-
mance. The optimum values for these parameters depend on network characteristics,
which can be stable through the network's lifetime, or change over time.
The main conguration parameters of the protocol are:
{ Buer size. This parameter controls the amount of carried notications. A too
low value can cause message loss, when a message is replaced on all nodes' buers
before reaching destination. Too high a value has an impact on performance and
resource consumption, as messages take space to be carried, computing power