Integrated services digital networks

Multimedia applications incorporate the use of more than one type of media, i.e., voice, video, data, text and image. With the advances in high-speed communication, the ability to transmit multimedia is becoming widely available. One of the means of transport for multimedia in distributed networks is Broadband Integrated Services Digital Network (B-ISDN). B-ISDN supports the transport of large volumes of data with a low error rate. It also handles the burstiness of multimedia traffic by providing dynamic bandwidth allocation. When multimedia is requested for transport in a distributed network, different Quality of Service (QOS) may be required for each type of media. For example, video can withstand more errors than voice. In order to provide, the most efficient form of transfer, different QOS media are sent using different channels. By using different channels for transport, jitter can impose skews on the temporal relations between the media. Jitter is caused by errors and buffering delays. Since B-ISDN uses Asynchronous Transfer Mode (ATM) as its transfer mode, the jitter that is incurred can be assumed to be bounded if traffic management principles such as admission control and resource reservation are employed. Another network that can assume bounded buffering is the 16 Mbps token-ring LAN when the LAN Server (LS) Ultimedia(TM) software is applied over the OS/2 LAN Server(TM) (using OS/2(TM)). LS Ultimedia(TM) reserves critical resources such as disk, server processor, and network resources for multimedia use. In addition, it also enforces admission control(1). Since jitter is bounded on the networks chosen, buffers can be used to realign the temporal relations in the media. This dissertation presents a solution to this problem by proposing a Feedback-based Multimedia Synchronization Technique (FMST) to correct and compensate for the jitter that is incurred when media are received over high speed communication channels and played back in real time. FMST has been implemented at the session layer for the playback of the streams. A personal computer was used to perform their synchronized playback from a 16 Mbps token-ring and from a simulated B-ISDN network.

This dissertation proposes YACAD (Yet Another Congestion Avoidance Design for ATM-based Networks), a congestion prevention model that includes admission control, traffic shaping, and link-by-link flow control for ATM-based networks. Network traffic in this model is composed of real-time traffic and data traffic. As real-time traffic is delay-sensitive and connection-oriented, its call acceptance is based upon the effective bandwidth at all nodes. Effective bandwidth is defined as a vector of bandwidth and maximum node delay. As data traffic can be either connection-oriented or connectionless, it is subject to link-by-link flow control based on a criterion known as effective buffer which is defined as a scalar of buffer size. Data traffic is not delay-sensitive but is loss-sensitive. Traffic shaping is imposed on real-time traffic to ensure a smooth inflow of real-time cells. YACAD also allocates a large buffer (fat bucket) to data traffic to accommodate sudden long bursts of data cells. Absence of data cell loss is a major feature of YACAD. Two simulation studies on the performance of the model are conducted. Analyses of the simulation results show that the proposed congestion avoidance model can achieve congestion-free networking and bounded network delays for real-time traffic at high levels of channel utilization. The maximum buffer requirements for loss-free cell delivery for data traffic, and the cell loss probabilities for real-time traffic are also obtained. In addition, results of performance comparisons to other similar models have shown that YACAD outperforms several other leaky-bucket based congestion control methods in terms of cell loss probability for real-time traffic. The simulation source program has also been verified using existing queueing theories, and the Paired-t Confidence Interval method with satisfactory results at 99% confidence level.

In order to guarantee a committed Quality of Service (QoS) to the users of a Broadband Integrated Services Digital Network (B-ISDN), preventive congestion control becomes critical, and is implemented through Call Acceptance Control (CAC) and Usage Parameter Control (UPC) functions. Currently, Asynchronous Transfer Mode (ATM) cells are equipped with a 1-bit Cell Loss Priority (CLP) field, which can be used for service-oriented and/or UPC marking. This creates a conflict, since these two marking approaches may have contradicting objectives, and are designed to operate independently. Moreover, by admitting excessive cells as marked traffic, this group is allowed to grow uncontrollably, thereby jeopardizing the QoS committed to other marked cells. This dissertation presents a solution to these problems by proposing a new 4-class priority strategy that unifies the two marking approaches, and is based on a 2-bit CLP field. The impacts of the new priority scheme are triple-fold: (I) For the UPC, a new scheme, the Forgiving Leaky Bucket (FLB), not only carries priorities through subnetwork boundaries, but also has the power of unmarking, i.e. forgiving, previously marked cells, depending on the bandwidth availability in the entering subnetwork. Forgiving will correct access-point bias, a phenomenon observed in internetworked ATM subnetworks of different congestion conditions. (II) At ATM switching nodes, a new space priority scheme is based on a hybrid of the Nested Threshold, and Push-Out cell discarding methods. This scheme is designed for the 4-class priority strategy, and improves the quality of the low priority traffic. (III) In interfacing High Speed Local Area Networks and Metropolitan Area Networks, idle bandwidth due to STM multiplexing is utilized to carry marked excessive cells of connection-oriented variable bit rate traffic, in addition to the service-oriented marking performed at transmitting stations. The resulting stream is then carried through internetworking points, subject to FLB adjustments. As a result, the STM and ATM subnetworks will support a uniform end-to-end priority strategy, essential for a B-ISDN. The proposed impacts are analyzed and compared with conventional implementations, and future directions are indicated.