A highly reliable multi-path routing scheme forad hocwireless networks

Fei Dai, Jie Wu*
2005 International Journal of Parallel, Emergent and Distributed Systems  
This paper presents a new routing scheme for ad hoc wireless networks that provides fresh routing information along active routes with affordable cost. The proposed routing mechanism, called proactive route maintenance (PRM), is used to replace the naive route mechanism in existing reactive (on-demand) routing protocols to enhance route reliability and reduce the frequency of expensive route discoveries. The assumption behind PRM is the communication locality in ad hoc wireless networks. That
more » ... , most data packets are transported along a few active routes. Data packets are forwarded via multiple optimal paths to meet certain QoS requirements, such as fault tolerance and load balance. Routing information is disseminated along active routes and advertised only by active nodes that forward data packets. Alternative paths are dynamically discovered and maintained by active nodes and their 1-hop neighbors (called passive nodes). The routing overhead in passive nodes is light. PRM maintains reliable end-to-end connections even in dynamic networks with relatively low overhead, and has the desirable properties including high delivery ratio, low latency, fair load distribution, self-healing and self-optimization. -15 allocation mechanism. Nevertheless, soft QoS routing is still possible, where the long-term statistic value of theses QoS metrics are enhanced for smooth communication. Routing in ad hoc networks is difficult for two reasons: Highly dynamic network topology and limited scarce bandwidth and energy resources. A perfect routing protocol would be providing accurate routing information when needed, while wasting no network resource in maintaining inactive routes. Ad hoc routing protocols are either proactive or reactive. Proactive protocols like DSDV [16] periodically disseminate routing information over the entire network regardless of neediness and suffer from high overhead. Reactive (i.e. ondemand) protocols such as DSR [9] and AODV [17] do not update routing information unless a new path is requested (route discovery) or an old path is broken (route recovery). Route discovery and recovery are usually conducted via network-wide flooding of route query (RREQ) packets, which causes route setup delay and high cost. Hybrid protocols like ZRP [6] use proactive approaches in small regions called zones and reactive approaches outside the local zones. However, the size of the zone is either too small to provide fresh information for an active route, or too large to be cost-effective. Multipath routing has been used in wired networks to improve throughput, fault tolerance and load balance. Due to the inter-route interference in wireless transmissions, multipath routing is less effective in achieving high throughput. Nevertheless, its abilities to provide multiple alternative paths and improve the distribution of communication loads are desirable for ad hoc networks, where wireless links fail frequently and mobile hosts suffer from limited power. In most existing multipath schemes for ad hoc networks [11 -13,15,21], multiple paths are divided into primary (i.e. active) paths that actually forward data packets, and backup paths that are activated only after active paths fail. Usually, a shortest path serves as the primary path, and others become backup paths. However, without maintenance, the backup paths may fail without alert, and cause longer delay and more packet losses. Simultaneously forwarding data packets via all paths can detect path failures promptly and achieve better load distribution. But this also causes out-of-order delivery and data transmission along non-optimal paths. This paper proposes a hybrid routing protocol that maintains robust multipath routes with relatively low overhead. This protocol uses the same route discovery mechanism as in reactive protocols, but the maintenance of the active routes is proactive, which adapts well to the highly dynamic networks, and reduces the frequency of route recoveries. The proposed proactive route maintenance (PRM) mechanism provides fresh routing information at where it is needed with affordable cost. PRM maintains a mesh containing multiple overlapping optimal and sub-optimal paths from the source to destination. All optimal paths are active. A data packet can travel to the destination via a randomly selected path. Sub-optimal paths serve as off-line backups, which are activated after all optimal paths have failed. As this mesh-structure is self-healing and self-optimizing, most link failures can be tolerated without causing route failure or non-optimal routing. PRM is a distributed routing scheme. A freshness-based mechanism similar to those in DSDV and AODV is used to ensure loop freedom. PRM can be used for soft QoS routing, where a multipath route is automatically adjusted to meet certain QoS requirements. In the case of a single path failure, the data traffic can switch to alternative paths to avoid packet losses. The automatic repair mechanism reduces the frequency of route recoveries, which also reduces the overall delay and delay-jitter. The traffic load of a connection is distributed to multiple paths, which lower the chance of
doi:10.1080/17445760500095035 fatcat:ejylzvxdkbgoxoi7uqz2u2xgoi