Flow control for the available bit rate service in asynchronous transfer mode networks
The goal of this thesis is the development and performance analysis of a flow control algorithm for the ABR (Available Bit Rate) service category in ATM (Asynchronous Transfer Mode) networks. ATM is a connection-oriented multiplexing and switching technique, that was developed for broadband-ISDN to transport data and multimedia streams with high bandwidth requirements in one integrated network. In ATM networks data is sent in packets of fixed size, called ATM cells, and Quality of Service (QoS) parameters are guaranteed for each individual connection. Since ATM networks have to support different applications, the ATM Forum (an association of manufacturers, network operators, users, and research institutes) has defined several service categories in its Traffic Management Specification. The ABR (Available Bit Rate) service category allows the use of remaining link bandwidth left unused by other service categories of higher priority. Another advantage of the ABR service is the guarantee of a minimum transmission rate per connection together with a low cell loss rate without the need for a specification of the ABR traffic characteristics. This makes ABR an attractive service category and an important feature of ATM networks. The ABR service category uses a flow control mechanism to adapt the transmission rate of ABR sources to the varying bandwidth left unused. For this, an end-to-end feedback control loop is established, providing information on the current condition of the network nodes (ATM switches) and the allowed transmission rate to the ABR source. If the Virtual Source / Virtual Destination (VS/VD) technique is used at an ATM switch along the network path from the ABR sender to the receiver, this flow control loop is split into two separate segments. The VS/VD switch is acting as an ABR destination for the upstream loop and as an ABR source for the downstream loop. The VS/VD technique offers the advantages of shortening the control loop and the feedback delay as well as controlling the individual ABR transmission rate inside of subnets, where VS/VD switches are located at the boundaries. This thesis meets the challenge of developing a novel VS/VD algorithm with the help of linear control theory. Existing works either do not address the special structure and tasks of VS/VD switches in their analytical analysis or use only heuristics and trial and error approaches for the VS/VD switch algorithm design. With the help of mathematical techniques it was possible to target important performance objectives, like stability and robustness, already during the design process of the novel VS/VD switch algorithm. A fair allocation of the ABR capacity to the ABR connections as well as an effective control of the VS/VD switch queue lengths were targeted as major performance objectives during the design of the algorithm. Beside the analytical performance evaluation an extensive analysis using simulations was performed. With the help of discrete event simulations various performance metrics for different network topologies, source configurations, and load conditions were investigated. From the analytical and simulation results it could be concluded that the newly developed VS/VD flow control algorithm does fully meet the defined performance requirements. It can be concluded that in this thesis a novel, simple ABR flow control algorithm based on linear control theory and tailored for VS/VD switches has been developed. The algorithm offers a fair, stable, and robust control of ABR sources including stable queue levels at the VS/VD switch and hence leading to a high throughput for ABR connections and an efficient utilization of the complete available bandwidth.
info:eu-repo/classification/ddc/004, Informatik, Telekommunikationsnetz, ATM, Dienstgüte, Bitrate, Kontrollfluss, Leistungsbewertung
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