There is provided a transmission system which realizes more flexible resource allocation. A resource management means 12, upon receipt of a resource allocation request including a minimum bandwidth and a maximum bandwidth, reduces allocated resources stored in an allocated-resource request table 13 to the corresponding minimum bandwidths. As such, the request is accepted with higher probability. When releasing an allocated resource, the resource management means 12 increases the allocated-resources of the allocated-resource requests to bandwidths within a range of the corresponding maximum bandwidths. Accordingly, the resources are utilized more effectively. When releasing the resource, the resource management means 12 notifies, by broadcast, all the communication apparatuses that free resources are increased. Thus, for the communication apparatus whose request has been rejected, the resource is allocatable.

Transmission system, bandwidth management apparatus, and bandwidth management method

Abstract In this paper, we present a comparison of two strategies which have recently been proposed for bandwidth allocation in Distributed Queue Dual Bus subnetworks of a Metropolitan Area Network. We study packet delays for connection oriented variable bit rate (VBR) traffic such as real-time data and compressed voice and video. It turns out that the Guaranteed Bandwidth Protocol is an excellent candidate for Connection Oriented Data Service in DQDB where support of delay sensitive VBR traffic is a major concern. In contrast to this, a modified version of the bandwidth balancing mechanism suffers from slow convergence to the desired bandwidth allocation. Additionally, it suffers from problems for network management.

Connection Oriented Data Service in DQDB.

The DQDB standard accepted by the IEEE Standards Board in 1990 is incomplete in the sense that it does not specify details of isochronous service and connection oriented data service. In this paper, we discuss the performance of a protocol which has been studied in all meetings of IEEE 802.6 since 1991. The Guaranteed Bandwidth (GBW) protocol for Connection Oriented Data Service turns out to be a very promising candidate for variable bit rate communication with predictable bandwidth requirements.

Connection oriented data service in DQDB

With the advent of multimedia communication services, transport of real-time traffic over metropolitan area networks (MANs) is becoming an important problem. We present a novel reservation arbitrated (RA) access protocol for multiplexing variable bit rate isochronous (VBRI) traffic such as packet voice and video over dual bus MANs in general and IEEE 802.6 MANs in particular. In combination with a cyclic release mechanism, RA access allows variable bit rate traffic sources (VBRSs) to capture and reserve some isochronous channels on a bandwidth on demand basis in a round robin fashion. For a reasonable bus length suitable for metropolitan coverage, it is possible to select operation parameters which enable contention free access in the reservation process. Bandwidth utilization can be further improved by employing a movable boundary option to efficiently integrate VBRI traffic with other traffic. System performances including packet loss ratio, packet delay, delay jitter, probability distribution of consecutive packet loss and channel utilization are analyzed by both theoretical computations and computer simulations for voice, video conference and motion video traffic. Results indicate that the protocol is fair and provides a nearly isochronous transport service while ensuring efficient bandwidth utilization, yielding substantial capacity improvements over pre-arbitrated (PA) access. Compared to queue-arbitrated (QA) access, RA access not only provides variable bit rate isochronous channels but also allows VBRSs to adapt to the reserved bandwidth during network congestion so that performance degradation can be minimized. RA access complements existing PA and QA access methods in 802.6 MANs to provide a complete traffic transport solution for all types of BISDN services.

Reservation arbitrated access—a bandwidth on demand protocol for multiplexing variable bit rate isochronous traffic over dual bus metropolitan area networks

Scheduling in a network is different from scheduling in a centralised environment where all resource requests are immediately known to the centralised scheduler. In metropolitan or wide area networks communication delays can be long and scheduling has to be carried out in parallel by distributed nodes with partial or delayed information. The extended DQDB protocol proposed by Budrikis for the accommodation of connection oriented time critical services, tries to augment the degree of resource utilisation of a dual bus shared medium network while meeting the quality of service requirements. The performance of the extended DQDB protocol will be compared to the performance of the queueing discipline the protocol tries to implement. We study the impact of internode distance and loading conditions on access delay distribution and demonstrate the effect of the presence of low priority traffic on the high priority traffic delays. These measurements are performed on a simplified centralised queueing model and on a detailed simulation model for the DQDB and the discrepancies between target and reality are discussed. >

Performance evaluation of the extended distributed queueing protocol for MAN

The distributed queue dual bus (DQDB) standard accepted by the IEEE Standards Board in 1990 is incomplete in the sense that it does not specify details of isochronous service and connection oriented data service. The authors discuss the performance of a protocol which has been studied in all meetings of IEEE 802.6 since 1991. The guaranteed bandwidth (GBW) protocol for connection oriented data service is a very promising candidate for variable bit rate communication with predictable bandwidth requirements. Simulation results of the GBW protocol are presented for various traffic scenarios. >

G. Werschmann

Papers

Connection oriented data service in DQDB simulation studies of the guaranteed bandwidth protocol