Appia: A Flexible Protocol Kernel Supporting Multiple Coordinated Channels

Distributed applications are becoming increasingly complex, often requiring the simultaneous use of several communication channels with different qualitiesof-service. This paper presents the Appia system, a protocol kernel that supports applications requiring multiple coordinated channels. Appia offers a clean and elegant way for the application to express inter-channel constraints, such as, for instance, that all channels should provide consistent information about the failures of remote nodes. These constraints can be implemented as protocol layers that can be dynamically combined with other protocol layers. ∗This work was partially supported by Praxis/ C/ EEI/ 12202/ 1998, TOPCOM. †Postal Address: FCUL, Campo Grande 1749-016 Lisboa, Portugal Phone: +351 217500613 Fax: +351 217500084