Comparison of Wireless Token Ring Protocol with IEEE 802.11 261 Comparison of Wireless Token Ring Protocol with IEEE 802.11 ˠ˴˹˴ ˘˺˸, ˗˾˸ ˟˸˸, ˥˶˻˼˴ ˗˴˴, ˝˸˹˹ ˞, ˔˽ P˼, ˥˴˽˴ ˦˸˺˴, P˴˼ ˩˴˴˼y˴ ˗˸˴˸ ˹ ˘˿˸˶˼˶˴˿ ˘˺˼˸˸˼˺ ˴˷ ˖˸ ˦˶˼˸˶˸ ˨˼˸˼y ˹ ˖˴˿˼˹˼˴, ˕˸˾˸˿˸y {˸˺˸, ˷˾˸, ˽˾, ˴˽, ˸˺˴, ˴˴˼y˴}˓˸˸˶.˵˸˾˸˿˸y.˸˷, ˷˴˴˓˴˻.˵˸˾˸˿˸y.˸˷ Abstract Wireless Token Ring Protocol (WTRP) is a medium access control (MAC) protocol for wireless networks. The MAC protocol through which mobile stations can share a common broadcast channel is essential in wireless networks. In a IEEE 802.11 network, the contention among stations is not homogeneous due to the existence of hidden terminals, partially connected network topology, and random access. Consequently, quality of service (QoS) is not provided. WTRP supports guaranteed QoS in terms of bounded latency and reserved bandwidth which are crucial real time constraints of the applications. WTRP is efficient in the sense that it reduces the number of retransmissions due to collisions. It is fair in the sense that each station use the channel for equal amount of time. The stations take turn to transmit and are forced to give up the right to transmit after transmitting for a specified amount of time. It is a distributed protocol that supports many topologies since not all stations need to be connected to each other or to a central station. WTRP is robust against single node failure. WTRP recovers gracefully from multiple simultaneous faults. WTRP has applications to inter-access point coordination in ITS DSRC, safety-critical vehicle-to-vehicle networking, home networking and provides extensions to sensor networks and Mobile IP. Keywords: Medium Access Control, Wireless Token Ring Protocol, IEEE802.11, IEEE802.4, Quality of Service, Intelligent Transportation Systems, Automated Highway Project, Mission Critical Systems, Home Networking. 1 Introduction Wireless Token Ring Protocol (WTRP) is a medium-access-control (MAC) protocol for applications running on wireless ad-hoc networks that provide quality of service. In ad hoc networks, participating stations can join or leave at any moment in time. This implies a dynamic topology. The MAC protocol through which mobile stations can share a common broadcast channel is essential in an ad-hoc network. Due to the existence of hidden terminals and partially connected network topology, contention among stations in an ad-hoc network is not homogeneous. Some stations can suffer severe throughput degradation in access to the shared channel when load of the channel is high, which also results in unbounded medium access time for the stations. This challenge is addressed as quality of service (QoS) in a communication network. In networks, QoS efforts have focused on network layer queuing and routing techniques [4,5]. In an unreliable medium such as wireless, providing QoS at the network layer using queuing and routing techniques is not sufficient. QoS must also be addressed at the data-link layer. The IEEE 802.11 [6] in PCF (Point Coordination Function) mode, the HiperLAN [16], and Bluetooth [17] achieve bounded latency by having a central station poll the slave stations. Most academic research has focused on this centralized approach [8,7]. The centralized approach is suitable for networks where only the last hop is wireless. In the centralized approach, the network is managed centrally from a central station. The Wireless Token Ring Protocol (WTRP) discussed in this paper is a distributed medium access control protocol for ad-hoc networks. Its advantages are robustness against single node failure, and support for flexible topologies, in which nodes can be partially connected and not all nodes need to have a connection with a master. Current wireless distributed MAC protocols such as the IEEE 802.11 (Distributed Coordination Function (DCF) mode) and the ETSI HIPERLAN do not provide QoS guarantees that are required by some applications. In particular, medium is not shared fairly among stations and medium-access time can be arbitrarily long [11,12]. As in the IEEE 802.4 [3] standards, WTRP is designed to recover from multiple simultaneous failures. One of the biggest challenges that the WTRP overcomes is partial connectivity. To overcome the problem of partial connectivity, management, special tokens, additional fields in the tokens, and new timers are added to WTRP. When a node joins a ring, it is required that the joining node be connected to the prospective predecessor and the successor. The joining node obtains this information by looking up its connectivity table. When a node leaves a ring, the predecessor of the leaving node finds the next available node to close the ring by looking up its connectivity table. Partial connectivity also affects the multiple token