Biomedical Engineering Reference
In-Depth Information
In the Infostation model [
9
] nodes communicate with each other with the help
of static infrastructure elements called infostations. They are permanently con-
nected, and provide a high bandwidth service in a specified area. The sender node
has to move close to a nearby infostation and upload it with its message. It is then
the responsibility of the infostation to deliver this message to the final destination
node, which is always outside the considered opportunistic network. In this
approach, messages experience very high delays.
The Shared Wireless Infostation Model (SWIM)[
10
] extends the technique used
in the infostation model. In this model, both node-to-node and node-to-base-station
forwarding is allowed for communications. Thus, the sender node can either
deliver the message directly to the base station, if it is within communication
range; or it delivers the message to a near neighboring node that will take it to the
base station whenever encountered. The message routing between the nodes fol-
lows an epidemic model [
13
]. Instead of aiming at a specific destination, any of the
infostations may act as the termination node for any given message. The SWIM
model, simulation results shows that there is a decrease in the delivery delays by
1.6-3.5 times as compared to infostation model.
The Mobile Ubiquitous LAN Extensions (Data-MULE) system [
11
] is a method
that is used to retrieve data from sparse wireless sensor networks. It is designed as
a three-tier architecture. The first level consists of sensor nodes that periodically
collect data from the surrounding environment. The second level consists of
mobile agents, named MULEs, which move randomly in the area covered by
sensors. These MULEs collect the data gathered by the sensor nodes. The third
level consists of access points and data repositories which receive information
from the MULEs. These access points are connected to a data warehouse where
the received data is stored for further processing.
In the Message-ferrying approach [
12
], some extra mobile agents called ferries
are employed in the network which offers a message relaying service. These agents
have high energy, speed, and buffer space as compared to the normal nodes. These
ferries move around in the network and collect messages from source nodes. Once
a message is given to the ferry, then it becomes the responsibility of the ferry node
to deliver it to the destination node. Message collection can take place in two
ways:
• Node-initiated message ferrying: The ferry node moves in the network fol-
lowing a predefined and known path. Every node in the network knows the path
that is taken by ferries. The sender node wishing to send a message moves closer
to the path followed by the ferry. After meeting with the ferry it transfers the
message to the ferry for delivery to the destination.
• Ferry-initiated message ferrying: The ferry node roams in the network fol-
lowing a fixed predetermined path. Any node wishing to communicate with
other nodes in the network sends a service request to the ferry, which also
includes its current position. After receiving the service request from the source
node, the ferry changes its path to meet the source node.
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