Survey of various routing approaches based on quality-of-service (QoS) criteria in MANET

Now a day, Mobile Adhoc Networks (MANET) gained a lot of popularity in the research community. People realized that there is a commercial value in MANETs with the successful solutions of the most basic but important problems in network layer. Mostly all the applications that attracted interest in traditional wired networks (e.g. Audio/Video Transfer, Video Conferencing, Watching Online Movies/Sports, Camera-enabled Messenger, Online Gaming etc.) would attract interest for MANETs as well. Since real-time multimedia communications will be common in MANETs, there has been an increasing motivation on the introduction of QoS in such networks. But, many characteristics of MANETs make QoS provisioning a difficult problem. In MANETs, providing QoS guarantees is very difficult and challenging than in traditional wired networks, mainly due to multihop communications, contention for channel access, node mobility and a lack of central coordination. However, in the last few years, much research attention has focused on providing QoS guarantees in MANET routing protocols. QoS routing protocol/mechanism is key issue in provision of QoS in MANETs. There are number of QoS routing approaches have been proposed in literature, focusing on different QoS metrics but no particular protocol/mechanism provides overall solution. There are some major open research issues in this area such as QoS metric selection and cost function design, Multi-class traffic, Scheduling mechanism at source, Packet prioritization for control messages, QoS routing that allows preemption, and QoS in Heterogeneous networks. There are still many open questions that must be solved to improve the performance of QoS-aware routing protocols such as bandwidth/delay estimation, route discovery, resource reservation, route maintenance, cross-layer design, energy consumption, multicast QoS routing etc.