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Real-Time Computing and Communication

Many real-time systems, such as Voice over IP, and military/industrial control systems, demand delay-guaranteed services to meet timing requirements of their applications. Our work has made contributions in developing delay guarantee techniques on real-time computing and communication in various systems, including differentiated services networks, wireless networks, component-based systems, and therma-aware systems.

Differentiated Services Networks

The differentiated services (DiffServ) model is well-known for its advantage of being able to support scalable Quality-of-Service (QoS) for aggregate traffic in computer networks. However, there is a fundamental dilemma: on one hand, the DiffServ model proposes to maintain no flow level information at core routers to help the system scale up; on the other hand, delay-guaranteed services naturally require fine-granularity treatments by the system. We solved this problem by proposing a utilization-based delay guarantee technique in DiffServ networks. With this new method, we were able to successfully employ a utilization-based admission control approach, which does not require explicit delay computation at admission time and hence is scalable to large systems.

Specifically, we developed the utilization-based delay guarantee technique in DiffServ networks in the following steps: (a) We first considered deterministic delay-guaranteed services, i.e., applications require hard deadlines; (b) We then extended deterministic delay-guaranteed services to statistical ones, which significantly improved the effectiveness of admission control by allowing increased statistical multiplexing of the network resources; (c) Finally, we applied our theoretical work into reality and implement a QoS-provisioning system that could be seamlessly integrated to the existing Voice-over-IP system. Our work made a substantial impact on the DiffServ community.

  1. S. Wang, D. Xuan, R. Bettati, and W. Zhao, "Providing Absolute Differentiated Services for Real-Time Applications in Static-Priority Scheduling Networks," in Proc. IEEE International Conference on Computer Communications (INFOCOM), April 2001.
  2. S. Wang, D. Xuan, R. Bettati, and W. Zhao, "Providing Absolute Differentiated Services with Statistical Guarantees in Static-Priority Scheduling Networks," in Proc. IEEE Real-Time Technology and Applications Symposium (RTAS), May 2001.
  3. S. Wang, D. Xuan, R. Bettati, and W. Zhao, "Differentiated Services with Statistical Real-Time Guarantees in Static-Priority Scheduling Networks," in Proc. IEEE Real-Time Systems Symposium (RTSS), December 2001.
  4. S. Wang, D. Xuan, R. Bettati, and W. Zhao, "A Study of Providing Statistical QoS Guarantees in Differentiated Services Networks," in Proc. IEEE International Symposium on Network Computing and Applications (NCA), April 2003.
  5. S. Wang, D. Xuan, R. Bettati, and W. Zhao, "Providing Absolute Differentiated Services for Real-Time Applications in Static-Priority Scheduling Networks," in IEEE/ACM Transactions on Networking (TON), Vol. 12, No. 2, pp. 326-339, April 2004. (Journal extension of [1])
  6. S. Wang, Z. Mai, W. Magnussen, D. Xuan, and W. Zhao, "Implementation of QoS-Provisioning System for Voice over IP," in Proc. IEEE Real-Time Technology and Applications Symposium (RTAS), December 2002.
  7. S. Wang, Z. Mai, D. Xuan, and W. Zhao, "Design and Implementation of QoS-Provisioning System for Voice over IP," in IEEE Transactions on Parallel and Distributed Systems (TPDS), Vol. 17, No. 3, pp. 276-288, March 2006. (Journal extension of [6])

Wireless Networks

The convenience of wireless communications has led to a growing use of wireless networks for both civilian and mission critical applications, many of which require delay-guaranteed communications. Wireless networks, however, are substantially different from their wired counterparts, and technologies developed for wired networks cannot be directly applicable.

The statistical nature of service provided by wireless links inherently precludes deterministic delay guarantees. Instead, we provided statistical delay-guaranteed services in wireless networks. We proposed a virtual traffic model, which assumed that some virtual traffic flows exist in addition to real ones. These virtual ones would consume the full unavailable bandwidth of wireless links and be assigned a strictly highest priority during scheduling. We observed that packet delays for real traffic in the original system were identical to delays in this virtual-traffic model. With this virtual traffic model, we could directly apply the utilization-based delay guarantee technique we developed in wired networks before to provide statistical delay-guaranteed services in wireless networks.

  1. S. Wang, R. Nathuji, R. Bettati, and W. Zhao, "Providing Statistical Delay Guarantees in Wireless Networks," in Proc. IEEE International Conference on Distributed Computing Systems (ICDCS), March 2004.
  2. S. Wang, R. Nathuji, R. Bettati and W. Zhao, "Real-Time Guarantees in Wireless Networks," in Resource Management in Wireless Networking, Mihaela Cardei, Ionut Cardei and Ding-Zhu Du (Eds.), Kluwer Academic Publishers, January 2005.

Component-based Systems

Component-based systems now serve as an important platform for developing a new generation of computer software. Reusability is a key factor that contributes to the great success of component technology. The reuse of components can lead to shortened software development cycles and reduced software development costs. However, all component models lack consideration for reusability of components in extending to provide delay-guaranteed services.

We developed a real-time component-based system that maintains the reusability of components while providing delay-guaranteed services. In the component architecture, we augmented the functional interfaces and context dependencies with contractually specified temporal interfaces and explicit time-related context dependencies, and made each component become what we call a “real-time component”. We built a component-based resource overlay, which was composed of resource overlay nodes – real-time components, to isolate the underlying resource management from applications. From the perspective of an application designer, the resource unit is a virtual resource (i.e., a real-time component) instead of the underlying resource. Based on component-based resource overlay, we could apply the utilization-based delay guarantee technique to efficiently and effectively provide delay-guaranteed services while maintaining the reusability feature.

  1. S. Wang, S. Rho, R. Bettati, and W. Zhao, "Toward Real-Time Component-based Systems," in Proc. IEEE International Real-time Systems Symposium (RTSS) Work-In-Progress Session, December 2004.
  2. S. Wang, S. Rho, Z. Mai, R. Bettati, and W. Zhao, "Real-Time Component-based Systems," in Proc. IEEE Real-Time and Embedded Technology and Applications Symposium (RTAS), March 2005.

Thermal-aware Systems


As power density in processors has increased exponentially in recent years, processors are prone to overheating caused by the large energy consumption. Temperature is becoming one of the big concerns in system design. Naturally, power management plays a key role in maintaining temperature. However, the majority of the literature focuses on power management for the purpose of saving energy, not for maintaining safe temperature levels. While energy and temperature are closely related, power control mechanisms and temperature control mechanisms are quite different. This is due to the fact that energy-aware techniques focus on dealing with the average energy consumption while temperature-aware ones focus on handling peak energy consumption.

We are interested in thermal-aware real-time systems, which have two major constraints: the delay constraint for jobs and the temperature constraint for the processor. Dynamic speed scaling is one of the major techniques for power management, which can control the power in the processor by dynamically changing the speed of the processor. Dynamic speed scaling allows for a trade-off between the performance metrics of delay and temperature in temperature-constrained real-time systems: to meet the delay constraint, we run the processor at a higher speed; to maintain the safe temperature levels, we run the process at a lower speed. In our research, we aim to investigate this trade-off under different dynamic speed scaling techniques.
  1. S. Wang and R. Bettati, "Reactive Speed Control in Temperature-Constrained Real-Time Systems," Best Paper Award, in Proc. Euromicro Conference on Real-Time Systems (ECRTS), July 2006.
  2. S. Wang and R. Bettati, "Reactive Speed Control in Temperature-Constrained Real-Time Systems," to appear in a special issue in the Real-Time Systems Journal (RTSJ), selected by ECRTS 2006 on May 2006. (Journal extension of [1])
  3. S. Wang and R. Bettati, "Delay Analysis in Temperature-Constrained Hard Real-Time Systems with General Task Arrivals," in Proc. IEEE Real-Time Systems Symposium (RTSS), December 2006. Technical Report, tamu-cs-tr-2006-5-3.