Abstract

GARCIA-HERNANDEZ, J.  and  GHANBARL, M.. Measurement of ATM layer quality of service parameters using OAM cells. J. appl. res. technol [online]. 2004, vol.2, n.2, pp.151-160. ISSN 2448-6736.

The measurement of the quality of service in ATM* networks involves the activation of the ATM layer management OAM functions. Once an ATM connection is set up, in-service performance monitoring based on OAM cells can be used to measure and estimate the ATM layer QoS parameters. In-service measurement of ATM layer QoS parameters such as cell delay variation, cell transfer delay, cell loss ratio, etc., is necessary to verify on one hand, if the network is meeting the requested QoS and on the other hand, if the users are receiving their promised QoS. Congestion conditions in ATM switches may cause gradual deteriorations in the quality of virtual paths or virtual channel connections in an ATM network. QoS measurement using OAM cells can accurately measure the overall quality of monitored ATM layer QoS parameters in order to detect such deteriorations before the service quality has dropped bellow an acceptable level. Several factors such as network load, congestion, bottlenecks, and increments in network load may affect the cell delay variation of video transmissions in an ATM network. In this work, several ATM layer QoS parameters have been measured on a VBR video source using OAM cells. The simulation results obtained show that with low network loads, the contribution of each individual ATM switch to the local and to the end-to-end cdv is not significant. In the presence of a bottleneck switch, the cdv presented by this switch becomes the dominant one at both local and end-to-end sides. When the network load is between 0.5 and 0.6, small increments in network load do not alter the buffer performance of the non-congested ATM switches, and low values of CDV can be obtained. In contrast, it was found that there is a critical load between 0.65 and 0.7 where small increments in network load may force the cdv to grow abruptly.

Keywords : Operation and Maintenance; Cell Delay Variation; Variable Bit Rate; Quality of Service.