Rao Naveed Bin Rais

Routing for disruption tolerant networks: taxonomy and design

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.

Towards truly heterogeneous internets: Bridging infrastructure-based and infrastructure-less networks

There is no doubt that networks are becoming increasingly heterogeneous and future internetworks will likely interconnect different types of networks including wired, infrastructure-based wireless as well as infrastructure-less wireless networks, a.k.a., multi-hop mobile ad-hoc networks (or MANETs). Integrating MANETs to infrastructure-based networks (wired or wireless) allows network coverage to be extended to regions where infrastructure deployment is sparse or nonexistent as well as a way to cope with intermittent connectivity. However, to date there are no comprehensive solutions that integrate MANETs to infrastructure-based networks. In this paper, we introduce a message delivery framework, MeDeHa++ that is able to bridge together infrastructure-based and infrastructure-less networks. Through extensive simulations, we demonstrate the benefits of MeDeHa++, especially in terms of the extended coverage it provides as well as its ability to cope with arbitrarily long-lived connectivity disruptions. Another important contribution of this work is to deploy and evaluate our message delivery framework on a real network testbed as well as conduct experiments in “hybrid” scenarios running partly on simulation and partly on real nodes.

Message delivery in heterogeneous networks prone to episodic connectivity

We present an efficient message delivery framework, called MeDeHa, which enables communication in an internet connecting heterogeneous networks that is prone to disruptions in connectivity. MeDeHa is complementary to the IRTF’s Bundle Architecture: besides its ability to store messages for unavailable destinations, MeDeHa can bridge the connectivity gap between infrastructure-based and multi-hop infrastructure-less networks. It benefits from network heterogeneity (e.g., nodes supporting more than one network and nodes having diverse resources) to improve message delivery. For example, in IEEE 802.11 networks, participating nodes may use both infrastructure- and ad-hoc modes to deliver data to otherwise unavailable destinations. It also employs opportunistic routing to support nodes with episodic connectivity. One of MeDeHa’s key features is that any MeDeHa node can relay data to any destination and can act as a gateway to make two networks inter-operate or to connect to the backbone network. The network is able to store data destined to temporarily unavailable nodes till the time of their expiry. This time period depends upon current storage availability as well as quality-of-service needs (e.g., delivery delay bounds) imposed by the application. We showcase MeDeHa’s ability to operate in environments consisting of a diverse set of interconnected networks and evaluate its performance through extensive simulations using a variety of scenarios with realistic synthetic and real mobility traces. Our results show significant improvement in average delivery ratio and a significant decrease in average delivery delay in the face of episodic connectivity. We also demonstrate that MeDeHa supports different levels of quality-of-service through traffic differentiation and message prioritization.

Resource aware routing in heterogeneous opportunistic networks

In heterogeneous scenarios, nodes greatly differ with respect to their capabilities and mobility patterns. Moreover, episodic connectivity in opportunistic networks further aggravates the problem of finding a suitable next-hop to obviate unnecessary utilization of network resources. In this paper, we present a Multiattribute Routing Scheme (MARS) based on “Simple Multiattribute Rating Technique” (SMART) that collects samples of vital information about a nodes different characteristics. This stochastic picture of a node behavior in multiple dimensions is then effectively employed in calculating its next-hop fitness. We also devise a method based on learning rules of neural networks which dynamically determines relative importance of each dimension to maximize next-hop utility of a node. With simulations, using synthetic and real mobility traces against well-known utility-based schemes, we show that MARS can achieve better delivery ratios despite introducing limited redundancy within the network.

Information-Centric Networks: Categorizations, challenges, and classifications

Information-Centric Networking (ICN) emerges as a promising approach for content dissemination and retrieval with a number of advantages including efficient content delivery, better bandwidth utilization and improved mobility support. In past few years, several ICN architectures have been proposed offering different set of features and characteristics, which makes it difficult to choose a particular architecture, given some network conditions and characteristics at hand. These characteristics include IP compatibility, and choice of naming structures etc. Besides, there is a little focus on a number of challenging areas including congestion control, availability, sporadic behavior, multi-source multi-destination and security etc. Moreover, it is not clear how ICN approaches behave with different emerging network environments such as user-centric networking, object-centric networking, Software-Defined networking and Cloud Computing. In this paper, we target all these issues together. First, we attempt to categorize different ICN architectures based on some common characteristics. Second, we identify a number of research challenges in the ICN domain and provide suggestions on mapping them to different ICN approaches. At the end, we bisect ICN approaches based on their characteristics and classify them on the basis of usability which helps a user choose a particular ICN approach given network requirements at hand.

Multi-Attribute Caching: Towards efficient cache management in Content-Centric Networks

Content Centric Networking (CCN) has gained much attention of the research community in past few years. The default caching strategy of CCN is to store at each content-router along the downloading path. While this helps in increasing content availability and quality-of-experience (QoE) by reducing delay and reducing server load, the approach is not resource-efficient as it introduces high cache redundancy. Hence, there is a need to devise efficient caching mechanisms that allows maximum availability of content while consuming minimum possible resources. In this paper, we propose Multi-Attribute Caching Strategy (MAC) for CCN Networks that is based on using multiple parameters instead of a single attribute. These parameters include hop count or distance, node degree, content popularity and available storage space at the nodes. The scheme promises to overcome inefficient cache utilization by intelligently selecting caching locations along the content delivery paths. Simulation results indicate that MAC reduces the cache load at each node while increasing network cache hit rate.

A dynamic caching strategy for CCN-based MANETs

Abstract Mobile environments are known for frequent disconnections among different parts of the network. This characteristic may lead to unavailability of data in some parts of the network, as the data source is not accessible due to partitions. Content Centric Networks (CCN) use in-network caching; this inevitably improves performance in mobile networks by decreasing the impact of dynamic topology. At the same time, limited storage space available at mobile nodes further signifies the need for an optimized decision regarding (1) which content to cache and (2) where to cache. With this in mind, we propose a Caching Strategy in CCN-MANET (CSCM) that dynamically adapts its caching decisions for each content, and selects optimal nodes for relocation of cached contents in case the old cache node moves to a disconnected region. In this paper, CSCM is implemented as a generic framework to work with existing cache approaches for improving data availability, data access time, and for reducing traffic and bandwidth consumption. Extensive simulation results show that CSCM improves performance in terms of content retrieval time, network traffic, and content relocation compared to traditional approaches.

Benchmarking and Modeling of Routing Protocols for Delay Tolerant Networks

Delay Tolerant Networks (DTN) are deployed to establish communications in challenging environments with frequent disruptions and delays due to intermittently connecting nodes, such as sparsely distributed wireless sensor networks and mobile ad hoc networks. Routing in such networks is difficult as nodes have little information about the state of the network that has time evolving topology. Therefore, nodes must store, carry, and forward messages towards destinations during opportunistic contacts. In recent years, numerous simulation based studies have been conducted for DTN protocols under various platforms, parameters, and mobility scenarios. However, most of the evaluations were limited in terms of: (a) number of protocols compared, (b) simulation parameters, and (c) DTN scenarios. This paper performs a detailed comparative analysis of ten popular DTN routing protocols. The protocols are benchmarked for the performance metrics, such as: (a) delivery ratio, (b) latency, and (c) message overhead, under the variance of: (a) buffer capacity, (b) message size, (c) message rate, and (d) size of network. The simulation results provide a deeper insight into a protocol’s strengths and weaknesses under diverse network conditions. As a further contribution, we proposed enhancements in the models of three routing schemes for DTNs. The proposed schemes autonomously adapt to the varying network conditions to reduce the messages’ replication frequency by finding optimal routes for messages among sources and destinations nodes. Simulation results indicated significant improvement in performance of the proposed enhanced schemes.

Analysis of TCP under Wireless Circumstances: A Performance Evaluation

With the emergence of wireless technology, and increase of mobile computing devices, the demand for the better network connectivity is the major interest of the users. Transmission Control Protocol (TCP) is the standard network protocol for communication in the Internet, but its performance drastically degrades over wireless networks, as TCP takes packet drop or collision as a sign of congestion. In this paper, we analyze TCPs performance over wireless networks using NS-2 Simulator. Unlike traditional performance evaluation methods for TCP over wireless networks, we consider different versions of TCP over different routing protocols. Moreover, we also consider the effectiveness of TCP both over infrastructure-based and infrastructure-less wireless networks. Simulation results show that TCPs performance varies from scenario to scenario both in infrastructure-based and ad-hoc wireless networks.