A system for constructing configurable high-level protocols

Abstract

Distributed applications often require sophisticated communication services such as multicast, membership, group RPC (GRPC), transactions, or support for mobility. These services form a large portion of the supporting software for distributed applications, yet the specific requirements of the service vary from application to application. Constructing communication services that are useful for multiple diverse applications while still being manageable and efficient is a major challenge. This dissertation focuses on improving the construction of complex communication services. The contributions of the dissertation are a new model for the construction of such services and the design and implementation of a supporting network subsystem. In this model, a communication service is decomposed into distinct micro-protocols, each implementing a specific semantic property. Micro-protocols have well-defined interfaces that use events to coordinate actions and communicate state changes, which results in a highly modular and configurable implementation. This model augments, rather than replaces, the conventional hierarchical protocol model. In this implementation, a conventional x-kernel protocol is replaced with a composite protocol in which micro-protocol objects are linked with a standard runtime system that externally presents the standard x-kernel interface. Internally, the runtime system provides common message services, enforces a uniform inter-face between micro-protocols, detects and generates events, and synchronously or asynchronously executes event handlers. The viability of the approach is demonstrated by performance tests for several different configurations of a suite of micro-protocols for a group RPC service. The micro-protocols in this suite implement multiple semantic properties of procedure call termination, message ordering, reliability, collation of responses, call semantics, membership, and failure. The tests were conducted while running within the x-kernel as a user level task on the Mach operating system. Additional micro-protocols for mobile computing applications validate the generality of the model. We designed micro-protocols for quality of service (QoS), transmitting and renegotiating QoS parameters during handoffs, as well as for mobility management, covering cell detection, handoff, and disconnection. This suite of micro-protocols can be configured to accommodate a range of different service requirements or even to mimic existing mobile architectures such as those found in the Crosspoint, PARC TAB, InfoPad, or DataMan projects.