Andres Albanese

Distributed registration and key distribution (DiRK)

This paper proposes a technique that can be used in a conferencing system to handle participants registration and key distribution in a decentralized and distributed way. The technique is named DiRK, an acronym derived from Distributed Registration and Key distribution. The basic idea of DiRK is to distinguish between active and passive participants in a particular conference session, and to have the active participants assist the session holder to register participants and distribute session keys accordingly. As an exemplary application, the paper also addresses the use of DiRK in the context of multimedia conferencing over the Internet Multicast Backbone (MBone).

PET - priority encoding transmission

With the explosion of information highways, network heterogeneity becomes a major issue. It is a challenge to write universal multimedia applications that run over interconnected packet networks with many subnetworks of unevenly distributed resources (processing, bandwidth, storage, and congestion control policies, etc.). Applications generate bursty traffic in today’s packet networks, causing unavoidable congestion, delays and losses. Thus, for applications such as real-time mutimedia, it is desirable for information to be compressed and prioritized so that the application can degrade gracefully under adverse network conditions.

Adaptable-bit-rate video services on DQDB access networks

Managing the bandwidth resource for an adaptable-bit-rate video service (in a MAN environment) provisioned with DQDB (distributed-queue dual-bus) access networks is the main objective of this work. Use is made of the bandwidth balancing (BWB) scheme to perform dynamic bandwidth allocation in addition to improving the fairness of the DQDB protocol. The steady-state average throughput measured at each station is directly proportional to its BWB modular value. Thus, the BWB modular value it the only control parameter required; no other overhead is necessary. The channel utilization can be nearly 100% when stations are overloaded. The transition of bandwidth reallocation makes the adaptable-bit-rate video codecs more feasible. Simulation examples are presented, and the relevant analytical formulae are derived.<<ETX>>

Information dispersal to improve quality of service on the Internet

Applications rely on network transmission services like dedicated ISDN or ATM to provide QoS guarantees for audio and video multimedia data in reasonable quality. This paper describes information dispersal as an alternative method to introduce robustness in error-sensitive and time-constrained when they use best-effort networks like the global Internet. We developed an experimental IP telephony application where the source audio stream is split and passed simultaneously to multiple, different Internet Service Providers. Before sending, the stream is protected with redundant data against eventual losses by an erasure-resilient FEC scheme utilizing a maximum distance separable code. This method assumes that routing paths are mutually independent. Extensive measurements were taken for voice transmission between two computers located on different continents and connected over the public Internet by using four different ISPs. The results show the increased robustness of the generated stream against uncorrelated burst delays and loses. It takes advantage of sharing the original and redundant data among all available connections.

Adaptive bandwidth balancing on DQDB networks

The bandwidth balancing (BWB) scheme has been used on distributed queue dual bus (DQDB) networks to improve the fairness of bandwidth allocation. Flexible dynamic bandwidth allocation can be achieved by using nonuniform BWB modular values. However, the local load condition in each station is ignored. The authors change the BWB scheme to be adaptive based on the local traffic intensity in each station. No additional hardware is required except a simple queue length monitor. The fairness of access delay time for heavily loaded networks is improved, while the original static BWB scheme remains more effective for lower load levels. The transient time for reaching throughput steady state is reduced at the cost of some overshooting. Variations of adaptive BWB schemes are discussed and analyzed numerically.<<ETX>>

Emulation of traffic congestion on ATM gigabit networks

The deployment of gigabit networks and broadband services has started to support multimedia applications; however, these gigabit networks are rarely saturate since only a few applications are able to stress the network. We consider a future scenario where the use of multimedia applications, such as audio and video teleconferencing in a multi-user environment, is expected to grow rapidly. Therefore, both customers and network providers need to foresee the performance and behavior of the network and applications in this scenario. From the customer’s point of view, it is important to develop procedures to perform traffic measurements and to be able to test the local ATM equipment. In this paper we propose a method for introducing heavy load into an ATM switch and at the User Network Interface (UNI) to study the performance and forecast evolved scenarios. In the experiments we used local equipment (ATM switch and workstations), local network management applications and diagnostics software. The emulated load is generated in a workstation, introduced into the ATM switch and intensified by replicating and re-circulating the cells. The method presented is an easy and affordable way to test performance and an alternative to traffic modeling. Several experiments have been performed and the measurements obtained are presented.