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A Graph Transformation System Model of Reliable Dynamic
Communication Networks for Location Transparent
Mobile Agents
M. Kurihara (Hokkaido Univ., Japan)
and M. Numazawa (Otaru Univ. Commerce, Japan)
Introduction
Distributed software technologies
Mobile agent technology
Future intelligent telecommunication technologies
research practice
Mobile agents are software agents that can move around the
network.
Introduction (2)
mobile agent network
Location transparent
Static: reliable
Dynamic: sound
Structure of this talk
1.Mobile agents & location transparency
2.Proxy networks (Reliablity)
3.Graph transformation system(Soundness)
Mobile Agents
Software agents that can move around the network
agent
stop resumemove
Host 1 Host 2
location transparent network
Location Transparency
The communications will not fail even if agent B has moved to B’ without any notice to A.
A
B B'communicatingmove
Can communicate?
In the location transparent network, yes.
Approaches to location transparency
(system-level implementation) Logging: the agents leave (in the agent
server) the trail information containing the next location
Brute Force: the system searches for the target agent by sending a query to every agent server
Registration: the system keeps the locations of all agents in a unique directory server, updating the information each time an agent makes a move
Proxy Networks(application-level implementation of
location transparency)
Basic idea: simple communication path for forwarding messages
A
B'B B"
proxy
proxy
target
Problems
Reliability: what if a proxy is abnormal?
Performance: O(the length of the path)
forward forward
Reliable and more efficient proxy networks
Reliable: one abnormal proxy is allowed. Performance: there is a shorter path.
Target
Special proxy
Normal proxies
Formal Representation(graph-theoretical definition of proxy networks)
A proxy network is a finite, simple, directed acyclic graph G=(V, E) that satisfy the following three conditions (in the next slide).
(The vertexes of V are called agents, and the directed edges of E are called links. By definition, a simple graph contains no parallel edges, which connect the same start and end vertexes; and an acyclic graph contains no circuits.)
Graph-theoretical definition of proxy networks (Contd.):
the three conditions
1. There exists a unique agent (called the target) with no outgoing links. (The agents other than the target are called proxies.)
2. There exists a unique proxy (called the special proxy) with exactly one outgoing link. The link should be connected to the target.
3. The remaining proxies (called normal proxies) have exactly two outgoing links.
Theorem 1 (Reliability)
For all pairs of distinct proxies v and w, there exists a path from v to the target t without passing through w.
v w t
Proof of Theorem 1
Start from v and follow an appropriate path as follows.
At normal proxies, follow a link whose end vertex is not w.
Repeat this process while you are at a normal proxy.
normal proxyw
Proof of Theorem 1 (Contd.)
Eventually, you will reach either the special proxy or the target.
If you are at the target, you are done.
Otherwise, you are at the special proxy.Follow the link connected to the target.
special proxy t
Graph Transformation Rule
utts usutEuVEV ,, )}),(),,{(},{(),(
s t s t u
(a) Move to a new host
s t s t u
(a) Move to a new place
s t
(b) Move to the special proxy
s t
u s t
(c) Move to a normal proxy
u s t
u v s t u v s t
(d) Bypass
Graph Transformation System
The initial network G0
)},{(},,{
),(
00
,000
tsEtsV
EVG ts
s t
Application of graph rewrite rules
nGGGG 210
nGG *0
Theorem 2 (Soundness)
If , then is a proxy network.
GG *0
G
Summary
1.Mobile agents
& location transparency2.Proxy networks
(Reliablity)3.Graph transformation system
(Soundness)
Future Work
Formal theory of more complex mobile agent systems
that might allow us (or even agents)to rigorously (or mechanically) reason about the dynamic nature of the networks.