In a typical slotted bus-based optical metropolitan network, the position of access node on the networkpsilas bus have a large impact on the network performance. We refer to this problem in data transmission as the unfairness property. In fact, the first nodes on the bus have priority over downstream nodes. Another factor which has a significant impact on the network performance is the choice of Timer value, which is used to create the fixed-size optical packet. An unsuitable choice of Timer values may lead to wasted network bandwidth. Indeed, small Timer values generate optical packets with very low filling ratios; while a very big Timer value leads to excessive packet creation delays (and therefore high access delays) when the arrival rate of electronic client packets becomes low. In this paper, we investigate the impact of Timer values on the network performance by simulating the slotted bus-based network that supports multi-service. In this context, we are interested in two study cases: with and without quality of service (QoS) Upgrade mechanism. Additionally, we will show that the slotted bus-based network with QoS Upgrade can improve the network performance, in terms of mean access delay and loss ratio of electronics packets clients, compared with unslotted bus-based network that supports variable-size optical packets