User-network oriented call control and traffic management in B-ISDNs.
Thesis DisciplineElectrical Engineering
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
This thesis presents a framework for call control and traffic management in B-ISDNs. Unlike the conventional focus on network capabilities, this thesis proposes a novel user-network oriented approach. This approach allows user terminals to perform control functions and to make use of service-specific information, such as the nature of calls and the nature of information within connections of the calls, in order to reduce call establishment delay and to minimise the bandwidth required by the connections. With B-ISDNs being expected to support general multiparty multimedia calls, a call control scheme is required to process such calls, and to establish and to manage the association among the parties (users) and the connections associated with each call. To this end, a hierarchical call control structure is proposed in this thesis. The structure allows the control functions to be carried out either by the network or by the user terminals depending on the level of terminal intelligence. The details of the call control structure along with the required signalling protocol are described. Examples of both simple and complex call establishments are provided in order to illustrate the proposed call control. Within each connection of a call, cell loss priority (CLP) can be used to identify cells having different loss probability requirements. Users can use CLP for tagging cells containing less essential information. Furthermore, we propose the possibility for users to police their traffic appropriately and to selectively tag any excess cells, considered expendable or else protected by end-to-end error recovery schemes, as being low priority; this avoids indiscriminate cell losses that would be caused by network usage of CLP. Not all connections will allow tagging of cells. Therefore, based on the existence or absence of pretagged or low priority cells in a connection, we can distinguish two classes of connections, namely connections without pretagged cells (the class of pure connections) and connections with pretagged cells (the class of mixed connections). The traffic management framework for pure connections is very well established, but this is not the case for mixed connections. Therefore it is of the interest in this thesis to present a traffic management framework for mixed connections, which includes connection admission control, usage parameter control, as well as buffer management and scheduling policy. Connection admission control algorithms, based upon a virtual bandwidth concept, involve a search for an equivalent bandwidth required by a connection. With mixed connections, there are two different QoS requirements. Existing methods which satisfy both requirements are either specific to some services, or time consuming, due to the required separate search for sufficient bandwidth to satisfy each QoS requirement. Considering these drawbacks, we propose two bandwidth allocation schemes in a homogeneous traffic environment and one scheme in a heterogeneous traffic environment. The methods require a single search for bandwidth and fully exploit the statistical dependency between the high and low priority traffic, and, as the result, allocate smaller bandwidth than previously proposed methods. After a connection has been admitted, a usage parameter control or policing algorithm is required, to monitor and to control the traffic within the connection during the information transfer phase, in order to ensure that the negotiated traffic parameters are not exceeded. The leaky bucket algorithm is the basis for the most popular policing schemes. In order to make sense of the large number of leaky bucket schemes, two classifications are proposed. Most of the schemes cannot take into account the presence of pretagged cells in mixed connections. Therefore, in order to overcome this drawback, we propose four modifications to the original leaky bucket scheme. Comparative studies based on both analytical and simulation techniques show that the newly proposed leaky bucket schemes can offer better quality of service for high priority traffic than earlier proposed leaky bucket schemes. The convergence within a network of high priority cells in pure connections and both high and low priority cells in mixed connections can lead to the interference between the cells in the sense that overload of low priority cells in a mixed connection can degrade not only the QoS of other mixed connections but also the QoS of pure connections. Therefore it is necessary for the network to implement a buffer management scheme to minimise such interference, while simultaneously trying to maximise the utilisation of network resources. A new buffer policy, called dual queues with limited cyclic service (DQCS), is developed and shown to achieve both objectives by both discrete-time performance analysis and simulation. The thesis concludes with proposals of some novel schemes for further study in order to develop an overall call control and traffic management framework for B-ISDNs.