Overview of Quality of Service for Distributed Objects

A gap exists between the socket-level Quality of Service (QoS) offered by communications researchers and the object-oriented programming being done at the application level. To bridge this gap, we introduce a framework for handling system properties such as QoS and partial failures. This framework extends the CORBA functional Interface Description Language (IDL) with a QoS Description Language (QDL). QDL specifies an application’s expected usage patterns and QoS requirements for a connection to an object. The QoS and usage specifications are at the object level (e.g., methods per second) and not at the communication level (e.g., bits per second). An application can have many connections to the same object, each with different system properties. QDL allows the object designer to specify system states, which represent the status of the QoS agreement for an object connection. The application can adapt to changing resources and partial failures by changing its behavior based on the system state of its object connections. Many hooks are provided for measuring and enforcing QoS agreements and for dispatching handlers when the agreements are violated.