A Survey of Routing Protocols that Support QoS in Mobile Ad Hoc Networks <s> QoS-aware Routing Based on Bandwidth Estimation <s> Early simulation experience with wireless ad hoc networks suggests that their capacity can be surprisingly low, due to the requirement that nodes forward each others' packets. The achievable capacity depends on network size, traffic patterns, and detailed local radio interactions. This paper examines these factors alone and in combination, using simulation and analysis from first principles. Our results include both specific constants and general scaling relationships helpful in understanding the limitations of wireless ad hoc networks. We examine interactions of the 802.11 MAC and ad hoc forwarding and the effect on capacity for several simple configurations and traffic patterns. While 802.11 discovers reasonably good schedules, we nonetheless observe capacities markedly less than optimal for very simple chain and lattice networks with very regular traffic patterns. We validate some simulation results with experiments. We also show that the traffic pattern determines whether an ad hoc network's per node capacity will scale to large networks. In particular, we show that for total capacity to scale up with network size the average distance between source and destination nodes must remain small as the network grows. Non-local traffic-patterns in which this average distance grows with the network size result in a rapid decrease of per node capacity. Thus the question “Are large ad hoc networks feasible?” reduces to a question about the likely locality of communication in such networks. <s> BIB001 </s> A Survey of Routing Protocols that Support QoS in Mobile Ad Hoc Networks <s> QoS-aware Routing Based on Bandwidth Estimation <s> Routing protocols for mobile ad hoc networks (MANETs) have been explored extensively in recent years. Much of this work is targeted at finding a feasible route from a source to a destination without considering current network traffic or application requirements. Therefore, the network may easily become overloaded with too much traffic and the application has no way to improve its performance under a given network traffic condition. While this may be acceptable for data transfer, many real-time applications require quality-of-service (QoS) support from the network. We believe that such QoS support can be achieved by either finding a route to satisfy the application requirements or offering network feedback to the application when the requirements cannot be met. We propose a QoS-aware routing protocol that incorporates an admission control scheme and a feedback scheme to meet the QoS requirements of real-time applications. The novel part of this QoS-aware routing protocol is the use of the approximate bandwidth estimation to react to network traffic. Our approach implements these schemes by using two bandwidth estimation methods to find the residual bandwidth available at each node to support new streams. We simulate our QoS-aware routing protocol for nodes running the IEEE 802.11 medium access control. Results of our experiments show that the packet delivery ratio increases greatly, and packet delay and energy dissipation decrease significantly, while the overall end-to-end throughput is not impacted, compared with routing protocols that do not provide QoS support. <s> BIB002
QoS-aware Routing based on Bandwidth Estimation (BEQR) BIB002 , a reactive routing protocol based on ad-hoc on demand distance vector (AODV), incorporates adaptive feedback and admission control by estimating the available bandwidth at each host during route discovery. BEQR supports both call admission and adaptive feedback to the source node. Bandwidth estimation is a crucial step in both the admission and adaptive feedback approaches in BEQR. BEQR presents two ways for nodes to estimate their residual bandwidth -Listen bandwidth estimation and Hello bandwidth estimation. Using the Listen bandwidth estimation method, hosts monitor their traffic flows and evaluate the ratio of free time and busy time to determine the available bandwidth. Using the Hello bandwidth estimation method, hosts disseminate their available bandwidth information to their neighbors through periodic Hello messages. Every host caches its twohop neighbors' bandwidth information. Therefore, each host determines its available bandwidth locally by comparing the raw channel bandwidth with the cached used bandwidth. The performance of BEQR using the Listen bandwidth estimation method is better in terms of overhead; whereas, the performance of BEQR using the Hello bandwidth estimation method is better in terms of the ability to quickly release bandwidth when routes fail. Route discovery in BEQR varies under different requirements. To perform call admission, source nodes put the requested bandwidth information in the route request (RREQ) packet header, and the hosts who receive the RREQ check their available bandwidth. If sufficient bandwidth is available, the intermediate nodes relay the RREQ packet; otherwise, they discard it. When the destination host receives a RREQ packet, it estimates the flow contention (i.e., the inter-flow interference caused by nearby nodes servicing different flows contending for channel access at the same time) BIB001 among the hops that will participate in the transmission of data for this new flow and then makes a final decision on flow call admission. If the flow is admitted, the destination sends a route reply (RREP) packet to the source using the reverse route taken by the RREQ packet. To perform adaptive feedback, the RREQ packet again carries the requested bandwidth. Intermediate hosts update the requested bandwidth value if their available bandwidth is less than the value recorded in the RREQ packet. The destination host makes a final adjustment to cover the bandwidth deduction caused by flow self-contention (i.e., the intra-flow interference caused by multiple nodes on the route servicing this flow contending for channel access at the same time), and it sends back a RREP with the admissible sending rate that can be supported by the route using the reverse route taken by the RREQ packet. Although bandwidth is not explicitly reserved during route discovery, soft bandwidth reservation automatically is made by monitoring network traffic, which aids in performing admission control and adaptive feedback. Route maintenance in BEQR is similar to AODV in that an error message, initiated by the host who cannot receive a Hello message from a downlink neighbor for a certain period, is forwarded back to the I 