Ulm University is located in the southern part of Germany. It was founded in 1967 and is therefore a rather young university. Nowadays there are about 7 000 students with main subjects in medicine, natural sciences, mathematics, economics, engineering and computer sciences. The computer science department has about 20 professors doing research and teaching in all major areas of computer science. Ulm University is partner of XtreemOS with the Aspectix Research Team as part of the Institute for Distributed Systems. The team and its 7 researchers are working on multimedia platforms, middleware systems for adaptive applications and fault tolerance.

• Virtual Nodes

The main task of UULM in XtreemOS is the development of a fault tolerance infrastructure called Virtual Nodes that can be used for grid applications but also for XtreemOS-internal services. Virtual Nodes are a framework providing multiple configurable implementations for replication support, e.g., Virtual Nodes provide active and passive replication protocols. The most innovative element of Virtual Nodes is the support of concurrency for replicated services due to different deterministic scheduling algorithms. For adding new replicas a special join protocol was developed that supports consistent state checkpoints even with concurrent service activities. Current work is the integration of Virtual Nodes technology into the XtreemOS job management services. The integration into security services is under consideration.

In cooperation with Vrije Universiteit Amsterdam (VUA), UULM has contributed to the Distributed Server system that allows clients to use a fixed server address. The corresponding server socket can be moved between different server instances. UULM is working on the integration of Distributed Server technology with Virtual Nodes, which allows clients to remain completely agnostic about replication.