Tolerant Networking (DTN) according to
communication situations (Nishiyama, 2014). DTN
is a method for coping with a network environment
where maintaining stable communication connection
is hard to achieve. When communication is
disconnected, portable devices accumulate data, and
then transmitted when communication is resumed.
Their proposed system apply MANET when there
are many portable devices in the surroundings, and
apply DTN when there are few. With such a method,
they achieved to cope with various network
environments.
As mentioned above, there are various works
aimed at supporting disaster evacuation. In order to
carry out safe and quick evacuation, it is necessary
to promptly identify places that are impassable (such
as the place where a fire occurs) and construct
evacuation route. These can be achieved by using
servers or sensors device installed in town.
However, these fixed devices may be damaged when
a disaster occurs and become unusable. Instead, our
proposed system uses only smartphones owned by
evacuees, and identifies places that are impassable
and construct evacuation routes.
3 AGENT BASE EVACUATION
SUPPORT SYSTEM
In this section, we describe our proposed system in
detail. The proposed system aims to provide an
optimal evacuation route for each user (hereafter we
call the evacuation user). Since the proposed system
maintains the map information of the evacuation
area, it is possible to calculate the shortest route to
the destination (i.e. safe place). However, at the time
of a disaster, there should be many occurrences of
unsuitable points for evacuation (hereafter we call
dangerous point) due to fire, building collapse, or
inundation. Since nobody knows these points before
the occurrence of a disaster, it is necessary to collect
the information during evacuation. When an
evacuation user finds a dangerous point, he or she
inputs the position information to the system. Then
the proposed system constructs a new evacuation
route avoiding this dangerous point, and provides it
to the user. At the same time, the system diffuses the
information about the dangerous point and new route
to other users’ smartphones. As a result, evacuation
users other than the discoverer can know the
dangerous point and avoid it in advance. In order to
realize this function, we use multiple mobile agents.
A multi-agent system is a system that consists of
multiple agents and achieves tasks by their
cooperative operations. The agents can be
categorized into two types: mobile agents and static
agents. A mobile agent is generated when it is
needed and executes a task through migrating among
communication sites including smartphones. Every
mobile agent has a unique identifier. A static agent
resides on communication site including, of course,
a smartphone. Unlike mobile agents, static agent has
no unique identifier. We describe the details of each
agent we use in the proposed system below.
3.1 Static Agents
3.1.1 Information Agent
Information Agent is a static agent residing on a
smartphone that interacts with mobile agents and
constructs evacuation routes. When requested from
the system, it creates mobile agent.
The information agent processes the request in
the following order. (i) It generates the requested
mobile agent. (ii) It acquires the information
necessary for the generated mobile agent from the
node management agent and passes it to the mobile
agent. (iii) It stores the mobile agent in a queue. It
periodically checks the queue, and dispatches the
mobile agents to the neighbouring smartphones.
When a mobile agent comes from another
smartphone, the information agent receives
information held by the mobile agent. Then it passes
the requested information to the arrived mobile
agent and store it in the queue in the same way as
the above step (iii). The information agent records
the unique identifier of the mobile agent that visited
the smartphone as well as it created in a list called
visitor list. The information agent requests the
visitor list of other smartphones when it
communicates with them. It then passes the received
visitor list to the mobile agent that needs it in the
queue. The mobile agent decides the next destination
from this visitor list.
The information agent constructs evacuation
routes based on the information it initially has, and
the information collected from the visited mobile
agents. The evacuation route is the route to the
destination avoiding dangerous points that are
currently known by the information agent. The
evacuation route is determined based on the
Dijkstra’s algorithm. The Dijkstra’s algorithm is an
algorithm for solving the shortest path problem
between two nodes in a graph, and was proposed by
Edgar Dijkstra in 1959 (Dijkstra, 1959). In the
proposed system, the graph consists of intersection
as the nodes, and the distances between intersections
Multi-Agent Base Evacuation Support System Considering Altitude
301