MESIS: the Architecture (2)

Management Environment for Secure and Interoperable Services

The AIF, ASF and ANF can make use of the whole set of functionality provided by the MESIS Lower Layer Facilities (LLF):

Agent Migration Facility (AMF); the AMF gives service designers the possibility to simply reallocate network resources and service components at run-time. Entities capable of reallocation are represented by agents, that can move in the network either via MA native migration methods or via standard specifications, such as CORBA Internet Inter-ORB Protocol and MASIF.

Agent Identification Facility (AIdF); the AIdF permits to dynamically assign tags to any entity in the system. Globally unique identifiers are the basis for the realization of the multiple naming systems provided by the ANF, that associates N different names with the same entity.

Agent Communication Facility (ACF); the ACF provides mechanisms and tools to simplify coordination and communication between entities. Agents in the same place interact by means of shared objects, such as blackboards and tuple spaces. Any place hosts a Local Resource Manager module that regulates agent access to the node resources. This module controls the authorization of agents and enforces the place security policy. Whenever one agent needs to share one resource with another agent that resides in a remote place, it is forced to migrate to that place. Outside the scope of the place, agents can perform coordinated tasks by exchanging messages eventually delivered to agents even in case of migration.

The above facilities are available in different flavors and depending on system and service needs. For instance, the ANF, which is based on the underlying AIdF, currently permits the co-existence of our naming native service deriving from DNS with the CORBA Naming Service. Other LDAP-compliant naming and directory services are under integration to let users and designers choose among multiple name spaces. Choosing which of the available facilities to use, and based on which implementation, typically depends on system- and application-specific considerations; for this reason, a flexible management environment has to give service designers the possibility to choose the proper solution among a wide variety of available ones.

From the MA programming paradigm, MESIS inherits the introduction of the migration facility as a basic DPE functionality: it is intrinsic to the paradigm the reallocation of entities that move close toward the locality that encloses the information to work upon. A DPE based on a different paradigm could choose different directions: a CORBA DPE would probably neglect this facility, on the base of allocation transparency. We claim that a DPE should implement all facilities, including the migration one, not to limit the flexibility and expressive capacity of a general management support.

 
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