We propose to study end to end delays in slotted optical MAN (Metropolitan Area Networks) ring networks. Edge nodes interconnect the fibre of the MAN and the client layer. We propose a mechanism based on IP traffic aggregations with QoS requirements in order to build optical packets. IP packet aggregation is performed in a loop manner by always beginning the aggregation cycle with the highest priority class. In order to overcome the drawbacks of the strict priority discipline, an algorithm depicting a probabilistic priority discipline is presented. The aggregation technique leads to increasing the filling ratio of an optical packet, and consequently, the bandwidth efficiency of an optical network. We present an analytical model in order to evaluate the performance of the aggregation mechanism. Secondly, we study the performance of the optical MAN ring with different packet formats. The MAC protocol is based on the ''empty slot'' procedure. Different queueing models based on the GI/G/1 queues with server interruptions are presented in order to compute mean packet delays according to the rank nodes.