Wireless network is a collection of hosts forming a network on the fly, using a fixed infrastructure. But Ad-hoc Wireless network is a collection of mobile hosts forming a network in the air, without using a fixed infrastructure. Some features of Ad-hoc Wireless network are lack of central coordination, mobility of hosts, dynamically varying network topology, and limited availability of resources make. There are so many solutions available to manage these features to provide better results. In this paper, we describe the various QoS for Ad-hoc Wireless network and review some of the QoS solutions proposed. Ad hoc wireless networks are baseless configurations, without any fixed infrastructure, self organizing networks formed by a set of mobile hosts connected through wireless links. These networks can be formed in the air, without requiring any fixed infrastructure. As these are infrastructure-less networks, each node should work as a router. As a router, the mobile host represents an intermediate node which forwards traffic on behalf of other nodes. If the destination node is not within the transmission range of the source node, the source node takes help of the intermediate nodes to communicate with the destination node.
[...] The QoS routing protocol should respond quickly in case of path breaks and re compute the broken path or bypass the broken link without degrading the level of QoS Ticket-based QoS routing protocol: Ticket-based QoS routing is a distributed QoS routing protocol for Ad-hoc Wireless Networks. It can tolerate imprecise state information during QoS route computation and exhibits good performance even when the degree of imprecision is high. The basic idea of the ticket-based probing protocol is that the source node issues a certain number of tickets and sends these tickets in probe packets for finding a QoS feasible path. [...]
[...] The hybrid approach incorporates features of both the table-driven and the on-demand approaches. MAC layer solutions The MAC protocol determines which node should transmit next on the broadcast channel when several nodes are competing for transmission on that channel. Some of the MAC protocols that provide QoS support for applications in Ad-hoc Wireless Networks are described below Cluster TDMA In bandwidth constrained Ad-hoc Wireless Networks, the limited resources available need to be managed efficiently. To achieve this goal, a dynamic clustering scheme is used in cluster TDMA. [...]
[...] The end-to-end delay for a packet depends on several factors such as, the size of the packet, current traffic load in the network, scheduling policy and processing capability of intermediate nodes, and capacity of links. As the delay prediction mechanism does not take into consideration some of the above factors, the predictions made by the location prediction mechanism may not be accurate, resulting in QoS violations for the real-time traffic Trigger based distributed QoS routing protocol: The trigger-based (on-demand) distributed QoS routing protocol was proposed by De et al. [...]
[...] The delay incurred in re-establishing a QoS session may cause some of the packets belonging to that session to miss their delay targets, which is not acceptable for applications that have stringent QoS requirements Imprecise state information: In most cases, the nodes in an ad hoc wireless network maintain both the link-specific state information and flow-specific state information. The link-specific state information includes bandwidth, delay, delay jitter, loss rate, error rate, stability, cost, and distance values for each link. The flow specific information includes session ID, source address, destination address, and QoS requirements of the flow (such as maximum bandwidth requirement, minimum bandwidth requirement, maximum delay, and maximum delay jitter). [...]
[...] Formation of clusters and selection of cluster-heads is done in a distributed manner. Clustering algorithms split the nodes into clusters such that they are interconnected and cover all the nodes. Three such algorithms used are, lowest-ID algorithm, highest degree (degree refers to number of neighbors which are within transmission range of a node) algorithm, and least cluster change (LCC) algorithm. In lowest-ID algorithm, a node becomes a cluster-head if it has the lowest ID among all its neighbors. In the highestdegree algorithm, a node with a degree greater than the degrees of all its neighbors becomes the cluster-head. [...]
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