tailieunhanh - Enabling Technologies for Wireless E-Business phần 6

tập thể dục giá trị một tác nhân, các pheromone hơn nó sẽ phát hành. Khi các đại lý di chuyển đến một ngã tư, họ sẽ ưu tiên chọn con đường với một nồng độ dày đặc hơn của pheromone. Một nhóm các đại lý điện thoại di động sẽ giải quyết các DOPS tập thể thông qua một cơ chế phản hồi tích cực: | 190 B. Yang and J. Liu fitness value an agent has the more pheromone it will release. When agents move to a crossroad they will preferentially select the path with a denser concentration of pheromone. A group of mobile agents will solve the DOPS collectively through a positive feedback mechanism agents that can find optimal solutions will have a higher fitness value their routes will have denser pheromone levels attracting more agents to choose them and bad agents with a lower fitness value will adjust their direction of travel or other behaviors by following the good agents. Eventually after a period of evolution controlled by positive feedback the entire system will reach an equilibrium state corresponding to the desired optimal solution. In this model changes to agents fitness value embody their self-adaptive behaviors as single entities while the positive feedback system embodies the selforganized behaviors of multiple agents. Security With code migration the mobile agent paradigm brings increased performance and flexibility to distributed systems. On the other hand the ability to move in itself brings significant security threats to both agents and hosts. Only a perfect solution to these serious security problems would enable the mobile agent paradigm to become the mainstream software technique for constructing large-scale distributed commercial applications. Issues and Countermeasures Two main types of threat need to be addressed agent-to-system and system-to-agent attacks. Jansen et al. 27 present a good survey of the threats faced by the mobile agent paradigm and the corresponding countermeasures. The agent-to-system category includes the kind of threats in which agents exploit security weaknesses to attack an agent system. This group mainly comprises masquerading denial of service and unauthorized access. Conversely the system-to-agent category includes threats in which systems attack agents that are situated within them. Again masquerading and .