The paper presents a topology-agnostic greedy protocol for network-on-chip routing. The proposed routing algorithm can tolerate any number of permanent faults, and is proven to be deadlock-free. We introduce a specialized variant of the algorithm, which is optimized for 2D mesh networks, both flat and wireless. The adaptiveness and minimality of several variants this algorithm are analyzed through graph-based simulations.
A first category of algorithms employ face routing based techniques to find paths around areas with faulty components. Maze routing is an important example of these techniques @cite_10 . An important advantage of such methods is that recent information on the status of each link node is required only by its neighbouring nodes, thus resulting in a low reconfiguration overhead. Furthermore, these methods provide full fault coverage: a route will be found whenever a path from a source node to its destination exists. The main disadvantage is that these methods are limited to planar graph topologies and cannot easily be extended to other topologies, such as 3D NoCs, wireless NoCs or a torus topology. Additionally, when a packet encounters an area with faulty components, the lack of information on the shape of this area may result in the message being routed along the border in a suboptimal direction, thus significantly increasing the path length.
@cite_10
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It was recently reported that all known face and combined greedy-face routing variants cannot guarantee message delivery in arbitrary undirected planar graphs. The purpose of this article is to clarify that this is not the truth in general. We show that specifically in relative neighborhood and Gabriel graphs recovery from a greedy routing failure is always possible without changing between any adjacent faces. Guaranteed delivery then follows from guaranteed recovery while traversing the very first face. In arbitrary graphs, however, a proper face selection mechanism is of importance since recovery from a greedy routing failure may require visiting a sequence of faces before greedy routing can be restarted again. A prominent approach is to visit a sequence of faces which are intersected by the line connecting the source and destination node. Whenever encountering an edge which is intersecting with this line, the critical part is to decide if face traversal has to change to the next adjacent one or not. Failures may occur from incorporating face routing procedures that force to change the traversed face at each intersection. Recently observed routing failures which were produced by the GPSR protocol in arbitrary planar graphs result from incorporating such a face routing variant. They cannot be constructed by the well known GFG algorithm which does not force changing the face anytime. Beside methods which visit the faces intersected by the source destination line, we discuss face routing variants which simply restart face routing whenever the next face has to be explored. We give the first complete and formal proofs that several proposed face routing, and combined greedyface routing schemes do guarantee delivery in specific graph classes or even any arbitrary planar graphs. We also discuss the reasons why other methods may fail to deliver a message or even end up in a loop. An important technique for discovering routes between two nodes in an ad-hoc network involves applying the face routing algorithm on a planar spanner of the network. Face routing guarantees message delivery in networks that contains large holes, where greedy algorithms fail. Existing techniques for constructing a suitable planar subgraph involve local tests that eliminate crossings between existing links by deleting some links. They do not test whether the deleted links actually create some crossings and some of the links are deleted needlessly. As a result, some of the routes found in face routing will have an unnecessarily large number of hops from source to destination. We consider a new local test for preprocessing a wireless network that produces a planar subgraph. The test is relatively simple, requires low overhead and does not eliminate existing links unless it is needed to eliminate a crossing, thus reducing overhead associated with multiple hops. This paper introduces a new, practical routing algorithm, Maze-routing, to tolerate faults in network-on-chips. The algorithm is the first to provide all of the following properties at the same time: 1) fully-distributed with no centralized component, 2) guaranteed delivery (it guarantees to deliver packets when a path exists between nodes, or otherwise indicate that destination is unreachable, while being deadlock and livelock free), 3) low area cost, 4) low reconfiguration overhead upon a fault. To achieve all these properties, we propose Maze-routing, a new variant of face routing in on-chip networks and make use of deflections in routing. Our evaluations show that Maze-routing has 16X less area overhead than other algorithms that provide guaranteed delivery. Our Maze-routing algorithm is also high performance: for example, when up to 5 links are broken, it provides 50 higher saturation throughput compared to the state-of-the-art. This paper is meant to be an illustration of the use of stochastic geometry for analyzing the performance of routing in large wireless ad hoc (mobile or mesh) networks. In classical routing strategies used in such networks, packets are transmitted on a pre-defined route that is usually obtained by a shortest-path routing protocol. In this paper we review some recent ideas concerning a new routing technique which is opportunistic in the sense that each packet at each hop on its (specific) route from an origin to a destination takes advantage of the actual pattern of nodes that captured its recent (re)transmission in order to choose the next relay. The paper focuses both on the distributed algorithms allowing such a routing technique to work and on the evaluation of the gain in performance it brings compared to classical mechanisms. On the algorithmic side, we show that it is possible to implement this opportunistic technique in such a way that the current transmitter of a given packet does not need to know its next relay a priori, but the nodes that capture this transmission (if any) perform a self-selection procedure to choose the packet relay node and acknowledge the transmitter. We also show that this routing technique works well with various medium access protocols (such as Aloha, CSMA, TDMA). Finally, we show that the above relay self-selection procedure can be optimized in the sense that it is the node that optimizes some given utility criterion (e.g. minimize the remaining distance to the final destination), which is chosen as the relay. The performance evaluation part is based on stochastic geometry and combines simulation as analytical models. The main result is that such opportunistic schemes very significantly outperform classical routing schemes when properly optimized and provided at least a small number of nodes in the network know their geographical positions exactly.