Showing papers on "Routing table published in 2010"

Symbiotic routing in future data centers

Abstract: Building distributed applications that run in data centers is hard. The CamCube project explores the design of a shipping container sized data center with the goal of building an easier platform on which to build these applications. CamCube replaces the traditional switch-based network with a 3D torus topology, with each server directly connected to six other servers. As in other proposals, e.g. DCell and BCube, multi-hop routing in CamCube requires servers to participate in packet forwarding. To date, as in existing data centers, these approaches have all provided a single routing protocol for the applications.In this paper we explore if allowing applications to implement their own routing services is advantageous, and if we can support it efficiently. This is based on the observation that, due to the flexibility offered by the CamCube API, many applications implemented their own routing protocol in order to achieve specific application-level characteristics, such as trading off higher-latency for better path convergence. Using large-scale simulations we demonstrate the benefits and network-level impact of running multiple routing protocols. We demonstrate that applications are more efficient and do not generate additional control traffic overhead. This motivates us to design an extended routing service allowing easy implementation of application-specific routing protocols on CamCube. Finally, we demonstrate that the additional performance overhead incurred when using the extended routing service on a prototype CamCube is very low.

Routing for disruption tolerant networks: taxonomy and design

Abstract: Communication networks, whether they are wired or wireless, have traditionally been assumed to be connected at least most of the time. However, emerging applications such as emergency response, special operations, smart environments, VANETs, etc. coupled with node heterogeneity and volatile links (e.g. due to wireless propagation phenomena and node mobility) will likely change the typical conditions under which networks operate. In fact, in such scenarios, networks may be mostly disconnected, i.e., most of the time, end-to-end paths connecting every node pair do not exist. To cope with frequent, long-lived disconnections, opportunistic routing techniques have been proposed in which, at every hop, a node decides whether it should forward or store-and-carry a message. Despite a growing number of such proposals, there still exists little consensus on the most suitable routing algorithm(s) in this context. One of the reasons is the large diversity of emerging wireless applications and networks exhibiting such "episodic" connectivity. These networks often have very different characteristics and requirements, making it very difficult, if not impossible, to design a routing solution that fits all. In this paper, we first break up existing routing strategies into a small number of common and tunable routing modules (e.g. message replication, coding, etc.), and then show how and when a given routing module should be used, depending on the set of network characteristics exhibited by the wireless application. We further attempt to create a taxonomy for intermittently connected networks. We try to identify generic network characteristics that are relevant to the routing process (e.g., network density, node heterogeneity, mobility patterns) and dissect different "challenged" wireless networks or applications based on these characteristics. Our goal is to identify a set of useful design guidelines that will enable one to choose an appropriate routing protocol for the application or network in hand. Finally, to demonstrate the utility of our approach, we take up some case studies of challenged wireless networks, and validate some of our routing design principles using simulations.

GeoDTN+Nav: Geographic DTN Routing with Navigator Prediction for Urban Vehicular Environments

Abstract: Position-based routing has proven to be well suited for highly dynamic environment such as Vehicular Ad Hoc Networks (VANET) due to its simplicity. Greedy Perimeter Stateless Routing (GPSR) and Greedy Perimeter Coordinator Routing (GPCR) both use greedy algorithms to forward packets by selecting relays with the best progress towards the destination or use a recovery mode in case such solutions fail. These protocols could forward packets efficiently given that the underlying network is fully connected. However, the dynamic nature of vehicular network, such as vehicle density, traffic pattern, and radio obstacles could create unconnected networks partitions. To this end, we propose GeoDTN+Nav, a hybrid geographic routing solution enhancing the standard greedy and recovery modes exploiting the vehicular mobility and on-board vehicular navigation systems to efficiently deliver packets even in partitioned networks. GeoDTN+Nav outperforms standard geographic routing protocols such as GPSR and GPCR because it is able to estimate network partitions and then improves partitions reachability by using a store-carry-forward procedure when necessary. We propose a virtual navigation interface (VNI) to provide generalized route information to optimize such forwarding procedure. We finally evaluate the benefit of our approach first analytically and then with simulations. By using delay tolerant forwarding in sparse networks, GeoDTN+Nav greatly increases the packet delivery ratio of geographic routing protocols and provides comparable routing delay to benchmark DTN algorithms.

OpenFlow Switching: Data Plane Performance

Abstract: OpenFlow is an open standard that can be implemented in Ethernet switches, routers and wireless access points (AP). In the OpenFlow framework, packet forwarding (data plane) and routing decisions (control plane) run on different devices. OpenFlow switches are in charge of packet forwarding, whereas a controller set up switch forwarding table on a per-flow basis, to enable flow isolation and resource slicing. We focus on the data path and analyze the OpenFlow implementation in Linux based PCs. We compare OpenFlow switching, layer-2 Ethernet switching and layer-3 IP routing performance. Forwarding throughput and packet latency in underloaded and overloaded conditions are analyzed, with different traffic patterns. System scalability is analyzed using different forwarding table sizes, and fairness in resource distribution is measured.

Energy-aware routing in data center network

Abstract: The goal of data center network is to interconnect the massive number of data center servers, and provide efficient and fault-tolerant routing service to upper-layer applications. To overcome the problem of tree architecture in current practice, many new network architectures are proposed, represented by Fat-Tree, BCube, and etc. A consistent theme in these new architectures is that a large number of network devices are used to achieve 1:1 oversubscription ratio. However, at most time, data center traffic is far below the peak value. The idle network devices will waste significant amount of energy, which is now a headache for many data center owners.In this paper, we discuss how to save energy consumption in high-density data center networks in a routing perspective. We call this kind of routing energy-aware routing. The key idea is to use as few network devices to provide the routing service as possible, with no/little sacrifice on the network performance. Meanwhile, the idle network devices can be shutdown or put into sleep mode for energy saving. We establish the model of energy-aware routing in data center network, and design a heuristic algorithm to achieve the idea. Our simulation in typical data center networks shows that energy-aware routing can effectively save power consumed by network devices.

Replication routing in DTNs: a resource allocation approach

Abstract: Routing protocols for disruption-tolerant networks (DTNs) use a variety of mechanisms, including discovering the meeting probabilities among nodes, packet replication, and network coding. The primary focus of these mechanisms is to increase the likelihood of finding a path with limited information, and so these approaches have only an incidental effect on such routing metrics as maximum or average delivery delay. In this paper, we present rapid, an intentional DTN routing protocol that can optimize a specific routing metric such as the worst-case delivery delay or the fraction of packets that are delivered within a deadline. The key insight is to treat DTN routing as a resource allocation problem that translates the routing metric into per-packet utilities that determine how packets should be replicated in the system. We evaluate rapid rigorously through a prototype deployed over a vehicular DTN testbed of 40 buses and simulations based on real traces. To our knowledge, this is the first paper to report on a routing protocol deployed on a real outdoor DTN. Our results suggest that rapid significantly outperforms existing routing protocols for several metrics. We also show empirically that for small loads, RAPID is within 10% of the optimal performance.

Energy-Efficient Beaconless Geographic Routing in Wireless Sensor Networks

Abstract: Geographic routing is an attractive localized routing scheme for wireless sensor networks (WSNs) due to its desirable scalability and efficiency. Maintaining neighborhood information for packet forwarding can achieve a high efficiency in geographic routing, but may not be appropriate for WSNs in highly dynamic scenarios where network topology changes frequently due to nodes mobility and availability. We propose a novel online routing scheme, called Energy-efficient Beaconless Geographic Routing (EBGR), which can provide loop-free, fully stateless, energy-efficient sensor-to-sink routing at a low communication overhead without the help of prior neighborhood knowledge. In EBGR, each node first calculates its ideal next-hop relay position on the straight line toward the sink based on the energy-optimal forwarding distance, and each forwarder selects the neighbor closest to its ideal next-hop relay position as the next-hop relay using the Request-To-Send/Clear-To-Send (RTS/CTS) handshaking mechanism. We establish the lower and upper bounds on hop count and the upper bound on energy consumption under EBGR for sensor-to-sink routing, assuming no packet loss and no failures in greedy forwarding. Moreover, we demonstrate that the expected total energy consumption along a route toward the sink under EBGR approaches to the lower bound with the increase of node deployment density. We also extend EBGR to lossy sensor networks to provide energy-efficient routing in the presence of unreliable communication links. Simulation results show that our scheme significantly outperforms existing protocols in wireless sensor networks with highly dynamic network topologies.

Systems and Methods for Fractional Routing Redundancy

Abstract: Systems and methods for fractional routing are described. An exemplary method may include receiving, by a first router, data information regarding routing by a first portion of a third router, receiving, by a second router, data information regarding routing by a second portion of a third router, wherein the data information regarding routing by the first portion and data information regarding routing by the second portion is not the same, routing, by the first router, data associated with the routing by the first portion of the third router, and routing by the second router, data associated with the routing by the second portion of the third router.

Stateless, affinity-preserving load balancing

Abstract: The invention relates to an architecture that facilitates load balancing among a plurality of hosts and preserve session affinity to a given host. An incoming stream of data packets that include packet sessions is input to one or more forwarding mechanisms for forwarding to one or more hosts. The forwarders generate a routing function that takes into consideration host availability, and distributes session packets according to the routing function. A session is distributed to the same host to preserve session affinity. When host availability changes, a new routing function is generated, such that any new session is routed according to the new routing function and existing sessions are routed according to the old routing function. When the old routing function becomes irrelevant, it is phased out. An optimization utilizes a maximally backward compatible hash function to minimize the differences between the old and new routing functions.

A tutorial on column generation and branch-and-price for vehicle routing problems

Abstract: This paper provides a tutorial on column generation and branch-and-price for vehicle routing problems. The main principles and the basic theory of the methods are first outlined. Some additional issues, including reinforcement of the relaxation or stabilization, complete the paper. For the sake of simplicity, this material is illustrated with the case of the vehicle routing problem with time windows.

Backpressure-based routing protocol for DTNs

Abstract: In this paper we consider an alternative, highly agile In this paper we consider an alternative, highly agile approach called backpressure routing for Delay Tolerant Networks (DTN), in which routing and forwarding decisions are made on a per-packet basis. Using information about queue backlogs, random walk and data packet scheduling nodes can make packet routing and forwarding decisions without the notion of end-to-end routes. To the best of our knowledge, this is the first ever implementation of dynamic backpressure routing in DTNs. Simulation results show that the proposed approach has advantages in terms of DTN networks.

Data center network system and packet forwarding method thereof

Abstract: A data center network system and a packet forwarding method are provided. The data center network includes a management server and a plurality of machines containing physical machines and virtual machines. The management server configures a logical media access control (MAC) address for each of the machines, wherein most significant bytes of each of the logical MAC addresses are set as 0. When a data packet is about to be sent from a physical machine, the physical machine executes an encapsulation procedure on the data packet for forwarding the data packet to an intermediate node between a transmitter and a receiver of the data packet, and the intermediate node executes a decapsulation procedure on the data packet for forwarding the data packet to the true receiver. Accordingly, the number of virtual machines exposed to the forwarding table of Ethernet switches can be effectively reduced.

DTN routing in body sensor networks with dynamic postural partitioning

Abstract: This paper presents novel store-and-forward packet routing algorithms for Wireless Body Area Networks (WBAN) with frequent postural partitioning. A prototype WBAN has been constructed for experimentally characterizing on-body topology disconnections in the presence of ultra short range radio links, unpredictable RF attenuation, and human postural mobility. On-body DTN routing protocols are then developed using a stochastic link cost formulation, capturing multi-scale topological localities in human postural movements. Performance of the proposed protocols are evaluated experimentally and via simulation, and are compared with a number of existing single-copy DTN routing protocols and an on-body packet flooding mechanism that serves as a performance benchmark with delay lower-bound. It is shown that via multi-scale modeling of the spatio-temporal locality of on-body link disconnection patterns, the proposed algorithms can provide better routing performance compared to a number of existing probabilistic, opportunistic, and utility-based DTN routing protocols in the literature.

Whanau: a sybil-proof distributed hash table

Abstract: Whanau is a novel routing protocol for distributed hash tables (DHTs) that is efficient and strongly resistant to the Sybil attack. Whanau uses the social connections between users to build routing tables that enable Sybil-resistant lookups. The number of Sybils in the social network does not affect the protocol's performance, but links between honest users and Sybils do.When there are n well-connected honest nodes, Whanau can tolerate up to O(n/ log n) such "attack edges". This means that an adversary must convince a large fraction of the honest users to make a social connection with the adversary's Sybils before any lookups will fail.Whanau uses ideas from structured DHTs to build routing tables that contain O(√n log n) entries per node. It introduces the idea of layered identifiers to counter clustering attacks, a class of Sybil attacks challenging for previous DHTs to handle. Using the constructed tables, lookups provably take constant time. Simulation results, using social network graphs from LiveJournal, Flickr, YouTube, and DBLP, confirm the analytic results. Experimental results on PlanetLab confirmthat the protocol can handle modest churn.

Method and system for extending routing domain to non-routing end stations

Abstract: A system is provided for facilitating assignment of a virtual routing node identifier to a non-routing node. During operation, the system assigns to a non-routing node coupled to a switch a virtual routing node identifier unique to the non-routing node. In addition, the system communicates reachability information corresponding to the virtual routing node identifier to other switches in the network.

CORE: a coding-aware opportunistic routing mechanism for wireless mesh networks [Accepted from Open Call]

Abstract: Opportunistic routing is a new routing paradigm that takes advantage of the broadcast characteristic of a wireless channel for data delivery in a wireless mesh network. Network coding has recently emerged as a new coding paradigm that can significantly improve the throughput performance of a WMN. In this article we explore the combination of opportunistic routing and network coding for improving the performance of a WMN. We first review existing opportunistic routing and coding-aware routing protocols, respectively, classify these protocols based on different criteria, and discuss their merits and drawbacks. We then propose a coding-aware opportunistic routing mechanism that combines hop-by-hop opportunistic forwarding and localized inter-flow network coding for improving the throughput performance of a WMN. Through opportunistic forwarding, CORE allows the next-hop node with the most coding gain to continue the packet forwarding. Through localized network coding, CORE attempts to maximize the number of packets that can be carried in a single transmission. Simulation results show that CORE can significantly improve the throughput performance of a WMN as compared with existing protocols.

Optimized InfiniBand TM fat-tree routing for shift all-to-all communication patterns

Abstract: Clustered systems have become a dominant architecture of scalable high-performance super computers. In these large-scale computers, the network performance and scalability is as critical as the compute-nodes speed. InfiniBandTM has become a commodity networking solution supporting the stringent latency, bandwidth and scalability requirements of these clusters. The network performance is also affected by its topology, packet routing and the communication patterns the distributed application exercises. Fat-trees are the topology structures used for constructing most large clusters as they are scalable, maintain cross-bisectional-bandwidth (CBB), and are practical to build using fixed-arity switches. In this paper, we propose a fat-tree routing algorithm that provides a congestion-free, all-to-all shift pattern leveraging on the InfiniBandTM static routing capability. The algorithm supports partially populated fat-trees built with switches of arbitrary number of ports and CBB ratios. To evaluate the proposed algorithm, detailed switch and host simulation models were developed and multiple fabric topologies were run. The results of these simulations as well as measurements on real clusters show an improvement in all-to-all delay by avoiding congestion on the fabric. Copyright © 2009 John Wiley & Sons, Ltd. The paper was presented in the International Super Computer 2007 conference in Dresden Germany.

On the Aggregatability of Router Forwarding Tables

Abstract: The rapid growth of global routing tables has raised concerns among many Internet Service Providers. The most immediate concern regarding routing scalability is the size of the Forwarding Information Base (FIB), which seems to be growing at a faster pace than router hardware can support. This paper focuses on one potential solution to this problem - FIB aggregation, i.e., aggregating FIB entries without affecting the forwarding paths taken by data traffic. Compared with alternative solutions to the routing scalability problem, FIB aggregation is particularly appealing because it is a purely local software optimization limited within a router, requiring no changes to routing protocols or router hardware. To understand the feasibility of using FIB aggregation to extend router lifetime, we present several FIB aggregation algorithms and evaluate their performance using routing tables and updates from tens of networks. We find that FIB aggregation can reduce the FIB table size by as much as 70% with small computational overhead. We also show that the computational overhead can be controlled through various mechanisms.

Addressing Manufacturing Challenges with Cost-Efficient Fault Tolerant Routing

Abstract: The high-performance computing domain is enriching with the inclusion of Networks-on-chip (NoCs) as a key component of many-core (CMPs or MPSoCs) architectures. NoCs face the communication scalability challenge while meeting tight power, area and latency constraints. Designers must address new challenges that were not present before. Defective components, the enhancement of application-level parallelism or power-aware techniques may break topology regularity, thus, efficient routing becomes a challenge.In this paper, uLBDR (Universal Logic-Based Distributed Routing) is proposed as an efficient logic-based mechanism that adapts to any irregular topology derived from 2D meshes, being an alternative to the use of routing tables (either at routers or at end-nodes). uLBDR requires a small set of configuration bits, thus being more practical than large routing tables implemented in memories. Several implementations of uLBDR are presented highlighting the trade-off between routing cost and coverage. The alternatives span from the previously proposed LBDR approach (with 30\% of coverage) to the uLBDR mechanism achieving full coverage. This comes with a small performance cost, thus exhibiting the trade-off between fault tolerance and performance.

Method and system for guaranteed end-to-end data flows in a local networking domain

Abstract: A local manager in a local networking domain may configure, in conjunction with one or more switching devices, a plurality of network and/or switching devices to establish guaranteed end-to-end data flows in the local networking domain for servicing applications and/or processes running in the network devices. The network devices supporting or using guaranteed end-to-end data flows may determine data flow requirements for each serviced application, and may communicate the determined data flow requirements to switching devices supporting the local manager, for configuring the guaranteed end-to-end data flows. Data flow requirements may comprise bandwidth, quality of service (QoS), security, and/or service level agreement (SLA) related parameters. The network devices may allocate networking resources to guarantee the end-to-end data flow for each application running in each network device. Data flow routing tables maybe maintained and/or updated based on use of existing guaranteed end-to-end data flows.

A power-efficient all-optical on-chip interconnect using wavelength-based oblivious routing

Abstract: We present an all-optical approach to constructing data networks on chip that combines the following key features: (1) Wavelength-based routing, where the route followed by a packet depends solely on the wavelength of its carrier signal, and not on information either contained in the packet or traveling along with it. (2) Oblivious routing, by which the wavelength (and thus the route) employed to connect a source-destination pair is invariant for that pair, and does not depend on ongoing transmissions by other nodes, thereby simplifying design and operation. And (3) passive optical wavelength routers, whose routing pattern is set at design time, which allows for area and power optimizations not generally available to solutions that use dynamic routing. Compared to prior proposals, our evaluation shows that our solution is significantly more power efficient at a similar level of performance.

Unified cache and peer-to-peer method and apparatus for streaming media in wireless mesh networks

Abstract: A method and apparatus are described including receiving a route request message to establish a streaming route, determining a cost of a reverse route and traffic load introduced by the requested streaming route, discarding the route request message if one of wireless interference constraints for the requested streaming route cannot be satisfied and quality of service requirements for the requested streaming route cannot be satisfied, pre-admitting the route request message if wireless interference constraints for the requested streaming route can be satisfied and if quality of service requirements for the requested streaming route can be satisfied, adding a routing table entry responsive to the pre-admission, admitting the requested streaming route, updating the routing table and transmitting a route reply message to an originator if requested content is cached, updating the route request message and forwarding the updated route request message if the requested content is not cached, receiving a route reply message and deleting the pre-admitted routing table entry if a time has expired.

Decentralized Coding Algorithms for Distributed Storage in Wireless Sensor Networks

Abstract: We consider large-scale wireless sensor networks with n nodes, out of which k are in possession, (e.g., have sensed or collected in some other way) k information packets. In the scenarios in which network nodes are vulnerable because of, for example, limited energy or a hostile environment, it is desirable to disseminate the acquired information throughout the network so that each of the n nodes stores one (possibly coded) packet so that the original k source packets can be recovered, locally and in a computationally simple way from any k(1 + ?) nodes for some small ? > 0. We develop decentralized Fountain codes based algorithms to solve this problem. Unlike all previously developed schemes, our algorithms are truly distributed, that is, nodes do not know n, k or connectivity in the network, except in their own neighborhoods, and they do not maintain any routing tables.

A reconfigurable fault-tolerant deflection routing algorithm based on reinforcement learning for network-on-chip

Abstract: We propose a reconfigurable fault-tolerant deflection routing algorithm (FTDR) based on reinforcement learning for NoC. The algorithm reconfigures the routing table through a kind of reinforcement learning---Q-learning using 2-hop fault information. It is topology-agnostic and insensitive to the shape of the fault region. In order to reduce the routing table size, we also propose a hierarchical Q-learning based deflection routing algorithm (FTDR-H) with area reduction up to 27% for a switch in an 8 x 8 mesh compared to the original FTDR. Experimental results show that in the presence of faults, FTDR and FTDR-H are better than other fault-tolerant deflection routing algorithms and a turn model based fault-tolerant routing algorithm.

Trust Management for Encounter-Based Routing in Delay Tolerant Networks

Abstract: We propose and analyze a class of trust management protocols for encounter-based routing in delay tolerant networks (DTNs). The underlying idea is to incorporate trust evaluation in the routing protocol, considering not only quality-of-service (QoS) trust properties (connectivity) but also social trust properties (honesty and unselfishness) to evaluate other nodes encountered. Two versions of trust management protocols are considered: an equal-weight QoS and social trust management protocol (called trust-based routing) and a QoS only trust management protocol (called connectivity-based routing). By utilizing a stochastic Petri net model describing a DTN behavior, we analyze the performance characteristics of these two routing protocols in terms of message delivery ratio, latency, and message overhead. We also perform a comparative performance analysis with epidemic routing for a DTN consisting of heterogeneous mobile nodes with vastly different social and networking behaviors. The results indicate that trust-based routing approaches the ideal performance of epidemic routing in delivery ratio, while connectivity-based routing approaches the ideal performance in message delay of epidemic routing, especially as the percentage of selfish and malicious nodes present in the DTN system increases. By properly selecting weights associated with QoS and social trust metrics for trust evaluation, our trust management protocols can approximate the ideal performance obtainable by epidemic routing in delivery ratio and message delay without incurring high message overhead.

R3: resilient routing reconfiguration

Abstract: Network resiliency is crucial to IP network operations. Existing techniques to recover from one or a series of failures do not offer performance predictability and may cause serious congestion. In this paper, we propose Resilient Routing Reconfiguration (R3), a novel routing protection scheme that is (i) provably congestion-free under a large number of failure scenarios; (ii) efficient by having low router processing overhead and memory requirements; (iii) flexible in accommodating different performance requirements (e.g., handling realistic failure scenarios, prioritized traffic, and the trade-off between performance and resilience); and (iv) robust to both topology failures and traffic variations. We implement R3 on Linux using a simple extension of MPLS, called MPLS-ff. We then conduct extensive Emulab experiments and simulations using realistic network topologies and traffic demands. Our results show that R3 achieves near-optimal performance and is at least 50% better than the existing schemes under a wide range of failure scenarios.

Multi-threaded collision-aware global routing with bounded-length maze routing

Abstract: Modern global routers use various routing methods to improve routing speed and the quality. Maze routing is the most time-consuming process for existing global routing algorithms. This paper presents two bounded-length maze routing (BLMR) algorithms (optimal-BLMR and heuristic-BLMR) to perform much faster routing than traditional maze routing algorithms. The proposed sequential global router, which adopts a heuristic-BLMR, identifies less-wirelength routing results with less runtime than state-of-the-art global routers. This study also proposes a parallel multi-threaded collision-aware global router based on a previous sequential global router. Unlike the conventional partition-based concurrency strategy, the proposed algorithm uses a task-based concurrency strategy. Experimental results reveal that the proposed sequential global router uses less wirelength and runs about 1.9X to 18.67X faster than other state-of-the-art global routers. Compared to the proposed sequential global router, the proposed parallel global router yields almost the same routing quality with average 2.71 and 3.12-fold speedup on overflow-free and hard-to-route benchmarks, respectively, when running on an Intel quad-core system.

Performance Analysis of Proactive and Reactive Routing Protocols for Ad hoc Networks

Abstract: Mobile Ad hoc networks are the collection of wireless nodes that can exchange information dynamically among them without pre existing fixed infrastructure. Because of highly dynamic in nature, performance of routing protocols is an important issue. In addition to this routing protocols face many challenges like limited battery backup, limited processing capability and limited memory resources. Other than efficient routing, efficient utilization of battery capacity and Security are also the major concern for routing protocols. This paper presents simulation based comparison and performance analysis on different parameters like PDF, Average e-e delay, Routing Overheads and Packet Loss. The study is about three main protocols DSR, AODV (Reactive) and DSDV (Proactive).

Virtual link aggregation of network traffic in an aggregation switch

Abstract: Access switches in a switching system may use virtual aggregated links. When a link between an aggregation switch and an access switch fails, the link failure may be reflected in the virtual aggregated link and data traffic to another access switch may be switched away from the failed switch. A forwarding table in the access switch stores a number of entries that each define a correspondence between destination addresses and an output identifier for the switch. At least a first output identifier includes an aggregated link that represents a first set of possible output links. At least a second output identifier includes a virtual aggregated link, associated with a second network switch that represents a second set of possible output links. Destination addresses in the forwarding table for the virtual aggregated link correspond to network devices connected to the second network switch.

Geo-opportunistic routing for vehicular networks [Topics in Automotive Networking]

Abstract: Road topology information has recently been used to assist geographic routing in urban vehicular environments to improve overall routing performance. However, the unreliable nature of wireless channels due to motion and obstructions still makes road topology assisted geographic routing challenging. In this article we begin by reviewing conventional road topology assisted geographic routing protocols, and investigate the robust routing protocols that address and help overcome the unreliable wireless channels. We then present topology-assisted geo-opportunistic routing that incorporates topology assisted geographic routing with opportunistic forwarding. That is, the routing protocol exploits the simultaneous packet receptions induced by the broadcast nature of the wireless medium and performs opportunistic forwarding via a subset of neighbors that have received the packet correctly. Our simulation results confirm TO-GO's superior robustness to channel errors and collisions compared to conventional topology-assisted geographic routing protocols.