Adaptation of UBR service category to HFC networks

This paper presents an algorithm to make the adaptation of the UBR service category to the operation on HFC (hybrid fibre coax) networks. The adaptation is based on the ERICA load computations for the ABR service category, with some modifications. ABR and UBR data streams are considered with equal priorities, and the set of all UBR active sources share an amount of bandwidth that is equal to the total bandwidth that an equal number of unconstrained ABR sources would have with the ERICA algorithm. This amount of bandwidth is totally dedicated to transmit UBR messages, and a service discipline is used to schedule the transmission of the messages. In the context of the choice of an appropriate service discipline, a new service discipline is proposed (named TDQ-transmission delay queueing). Its principle of operation is to schedule the message that has the lowest value of the ratio T/sub t//(T/sub t/+T/sub w/), where T/sub t/ is the expected transmission time of the message, and T/sub w/ is the time that the message has already waited for transmission. As shown by simulations, this procedure reduces substantially the standard deviation of the waiting times of the messages, achieving lower values than those of other service disciplines, namely SCFQ, W2FQ+, and WFQ. Simulations also indicate that TDQ has very low delay bounds, because maximum delays obtained were the lowest, as low of those of W2FQ+ and lower than those of WFQ and of SCFQ. The new service discipline does not offer protection and therefore fairness, but it can be associated with ether mechanisms in order to provide them.