Most of the QoS routing schemes proposed so far require periodic exchange of QoS state information among routers, imposing both communication overhead on the network and processing overhead on core routers. Furthermore, stale QoS state information causes the performance of these QoS routing schemes to degrade drastically. In order to circumvent these problems, we focus on localized QoS routing schemes where the edge routers make routing decisions using only local information and thus reducing the overhead at core routers. We first describe virtual capacity based routing (vcr), a theoretical scheme based on the notion of virtual capacity of a route. We then propose proportional sticky routing, an easily realizable approximation of vcr and analyze its performance. We demonstrate through extensive simulations that adaptive proportional routing is indeed a viable alternative to the global QoS routing approach.

Most of the QoS routing schemes proposed so far require periodic exchange of QoS state information among routers, imposing both communication overhead on the network and processing overhead on core routers. Furthermore, stale QoS state information causes the performance of these QoS routing schemes to degrade drastically. In order to circumvent these problems, we focus on localized QoS routing schemes where the edge routers make routing decisions using only "local" information and thus reducing the overhead at core routers. We first describe virtual capacity-based routing (VCR), a theoretical scheme based on the notion of virtual capacity of a route. We then propose proportional sticky routing (PSR), an easily realizable approximation of VCR and analyze its performance. We demonstrate through extensive simulations that adaptive proportional routing is indeed a viable alternative to the global QoS routing approach.

The successful operation of mission critical systems requires a sophisticated control network which provides for the real-time delivery of data from a very large number of diverse sources such as sensors, audio/video surveillance, computational sources, etc., as well as remote monitoring and diagnosis sources. It is expected that many of the traffic sources will be in the form of periodic sources with real-time requirements. In this study, we propose fast scheduling algorithms for multiplexing periodic source flows with real-time delivery requirements. We assume a single switch environment with periodic source flows being supported over a constant bit rate (CBR) type circuit. We undertake a systematic study beginning from the simplest scenario where all traffic flows consist of data frames of the same size and with the same real-time delay requirement. In this case, we prove that the FCFS algorithm is optimal. We conclude with the most difficult case of examining CBR flows of variable bandwidth requirements and variable delay requirements. Algorithms and analysis are presented for all the cases. The simulation results show the substantial performance gains provided by the proposed algorithms.

Video delivery from a server to a client across a network is an important component of many multimedia applications. While delivering a video stream across a resource constrained network, loss of frames may be unavoidable. Under such circumstances, it is desirable to find a server transmission schedule that can efficiently utilize the network resources while maximizing the perceived quality-of-service (QoS) at the client. To address this issue, we introduce the notion of selective frame discard at the server and formulate the optimal selective frame discard problem using a QoS based cost function. Given network bandwidth and client buffer constraints, we develop an O(N log N) algorithm to find the minimum number of frames that must be discarded in order to meet these constraints. The correctness of the algorithm is also formally established. Since the computational complexity of the optimal algorithm for solving the optimal selective frame discard problem is prohibitively high in general, we also develop several efficient heuristic algorithms for selective frame discard. These algorithms are evaluated using JPEG video traces.

The paper examines the efficient layout of virtual paths (VPs) in an ATM network. The ATM network consists of ATM switches and their attached network end users, which may be gateways, routers, and hosts. The physical topology, the offered traffic, and call setup matrices of the network end users are assumed to be given. The problem is formulated as a flow-based optimization problem. A heuristic approach is presented which (i) establishes VPs according to physical network-specific and application-specific constraints and a cost function, (ii) provides multipaths between each source destination user pair to minimize the cell blocking probability and to increase network resilience, and (iii) uses a novel VP combining process which is guaranteed to always satisfy the switching constraints. Simulation results are presented for the proposed VP planning policy. Guidelines for the design of robust VP layouts and the efficient establishment of VCs are also presented.>