Zartash Afzal Uzmi

MMAC: a mobility-adaptive, collision-free MAC protocol for wireless sensor networks

Mobility in wireless sensor networks poses unique challenges to the medium access control (MAC) protocol design. Previous MAC protocols for sensor networks assume static sensor nodes and focus on energy-efficiency. In this paper, we present a mobility-adaptive, collision-free medium access control protocol (MMAC) for mobile sensor networks. MMAC caters for both weak mobility (e.g., topology changes, node joins, and node failures) and strong mobility (e.g., concurrent node joins and failures, and physical mobility of nodes). MMAC is a scheduling-based protocol and thus it guarantees collision avoidance. MMAC allows nodes the transmission rights at particular time-slots based on the traffic information and mobility pattern of the nodes. Simulation results indicate that the performance of MMAC is equivalent to that of TRAMA in static sensor network environments. In sensor networks with mobile nodes or high network dynamics, MMAC outperforms existing MAC protocols, like TRAM A and S-MAC, in terms of energy-efficiency, delay, and packet delivery.

Minimizing flow completion times in data centers

For provisioning large-scale online applications such as web search, social networks and advertisement systems, data centers face extreme challenges in providing low latency for short flows (that result from end-user actions) and high throughput for background flows (that are needed to maintain data consistency and structure across massively distributed systems). We propose L2DCT, a practical data center transport protocol that targets a reduction in flow completion times for short flows by approximating the Least Attained Service (LAS) scheduling discipline, without requiring any changes in application software or router hardware, and without adversely affecting the long flows. L2DCT can co-exist with TCP and works by adapting flow rates to the extent of network congestion inferred via Explicit Congestion Notification (ECN) marking, a feature widely supported by the installed router base. Though L2DCT is deadline unaware, our results indicate that, for typical data center traffic patterns and deadlines and over a wide range of traffic load, its deadline miss rate is consistently smaller compared to existing deadline-driven data center transport protocols. L2DCT reduces the mean flow completion time by up to 50% over DCTCP and by up to 95% over TCP. In addition, it reduces the completion for 99th percentile flows by 37% over DCTCP. We present the design and analysis of L2DCT, evaluate its performance, and discuss an implementation built upon standard Linux protocol stack.

Performance comparison of ad hoc wireless network routing protocols

In recent years many protocols for ad hoc wireless networks have been developed but very little information is available on the performance of these protocols. After describing the desirable characteristics of an ad hoc network routing protocol this paper provides an overview of four existing ad hoc wireless routing protocols, which are distance sequence distance vector (DSDV), ad hoc on demand distance vector (AODV), dynamic source routing (DSR) and temporally ordered routing algorithm (TORA). The performance comparison of these four protocols is based on simulations performed using network simulator-2. The performance parameters analyzed are the mobility rate, network load and network size. The paper describes all the parameters used for the simulations in detail and then compares each routing protocols simulation results before arriving at a conclusion as to which is the best one for ad hoc networks.

SMALTA: practical and near-optimal FIB aggregation

IP Routers use sophisticated forwarding table (FIB) lookup algorithms that minimize lookup time, storage, and update time. This paper presents SMALTA, a practical, near-optimal FIB aggregation scheme that shrinks forwarding table size without modifying routing semantics or the external behavior of routers, and without requiring changes to FIB lookup algorithms and associated hardware and software. On typical IP routers using the FIB lookup algorithm Tree Bitmap, SMALTA shrinks FIB storage by at least 50%, representing roughly four years of routing table growth at current rates. SMALTA also reduces average lookup time by 25% for a uniform traffic matrix. Besides the benefits this brings to future routers, SMALTA provides a critical easy-to-deploy one-time benefit to the installed base should IPv4 address depletion result in increased routing table growth rate. The effective cost of this improvement is a sub-second delay in inserting updates into the FIB once every few hours. We describe SMALTA, prove its correctness, measure its performance using data from a Tier-1 provider as well as Route-Views. We also describe an implementation in Quagga that demonstrates its ease of implementation.

Interdomain path computation: Challenges and Solutions for Label Switched Networks

For label switched networks, such as MPLS and GMPLS, most existing traffic engineering solutions work in a single routing domain. These solutions do not work when a route from the ingress node to the egress node leaves the routing area or autonomous system of the ingress node. In such cases, the path computation problem becomes complicated because of the unavailability of the complete routing information throughout the network. This is because service providers usually choose not to leak routing information beyond the routing area or AS for scalability constraints and confidentiality concerns. This article serves two purposes. First, it provides a description of the existing and ongoing work in interdomain TE within the IETF. This information is currently found in various Internet drafts and has not yet been collectively presented in a single document. To this end, a summary of both existing path computation architectures - PCE-based and per-domain - is provided. Second, it compares two per-domain path computation schemes in terms of the total number of LSPs successfully placed and average number of domains crossed, without assuming availability of complete topology information. We notice that the two per-domain path computation schemes, proposed in [1, 2], have comparable path computation complexities and setup latencies.

Medium access control with mobility-adaptive mechanisms for wireless sensor networks

Mobility in wireless sensor networks poses unique challenges to the Medium Access Control (MAC) protocol design. Previous MAC protocols for sensor networks assume static sensor nodes and focus on energy-efficiency. In this paper, we present MMAC, a mobility-adaptive, collision-free MAC protocol for mobile sensor networks. MMAC caters for both weak mobility (e.g. topology changes, node joins and node failures) and strong mobility (e.g. concurrent node joins and failures, and physical mobility of nodes). When using MMAC, nodes are allowed to transmit at particular time-slots, based on the traffic information and mobility pattern of the nodes. Allowing transmission at particular time-slots makes MMAC a scheduling-based protocol, thereby guaranteeing collision avoidance. Simulation results indicate that the performance of MMAC is equivalent to that of TRAMA in static sensor network environments. In sensor networks with mobile nodes or high network dynamics, MMAC outperforms existing MAC protocols, including TRAMA and S-MAC, in terms of energy-efficiency, delay and packet delivery.

CSN: a network protocol for serving dynamic queries in large-scale wireless sensor networks

A fundamental problem that confronts future applications of sensor networks is how to locate efficiently the sensor node that stores a particular data item. Distributed hash table (DHT) based Internet peer-to-peer (P2P) protocols provide near-optimum data lookup times for queries made on networks of distributed nodes. A generic mapping of these protocols to sensor networks is, however, perceived as difficult (Ratnasamy, S. et al., Mobile Networks and Applications, - MONET 2003). We present a novel DHT based network protocol for sensor networks - chord for sensor networks (CSN) - for which bounded times for data lookup, in the order of O(logN) messages, can be achieved in an energy efficient manner. CSN makes the system lifetime of the sensor network proportional to its effective use. Furthermore, CSN scales well to large-scale sensor networks when the information about other nodes logarithmically increases with an increase in the number of sensor nodes.

Optimized java binary and virtual machine for tiny motes

We have developed TakaTuka, a Java Virtual Machine optimized for tiny embedded devices such as wireless sensor motes. TakaTuka requires very little memory and processing power from the host device. This has been verified by successfully running TakaTuka on four different mote platforms. The focus of this paper is TakaTuka’s optimization of program memory usage. In addition, it also gives an overview of TakaTuka’s linkage with TinyOS and power management. TakaTuka optimizes storage requirements for the Java classfiles as well as for the JVM interpreter, both of which are expected to be stored on the embedded devices. These optimizations are performed on the desktop computer during the linking phase, before transferring the Java binary and the corresponding JVM interpreter onto a mote and thus without burdening its memory or computation resources. We have compared TakaTuka with the Sentilla, Darjeeling and Squawk JVMs.

Online routing of bandwidth guaranteed paths with local restoration using optimized aggregate usage information

We investigate the problem of distributed online routing of bandwidth guaranteed paths with local restoration. A unified model is proposed that captures the bandwidth sharing characteristic of backup paths that provision local restoration, corresponding to different fault models. We apply the model to describe bandwidth sharing on backup paths for varying degrees of network state information. The extent of backup bandwidth sharing depends on the amount of network state information made available through routing protocols. A key design criterion for traffic engineering schemes is to maximize the sharing between backup paths, while minimizing this protocol overhead. M.S. Kodialam and T.V. Lakshman (see Proc. Infocom, p.376-85, 2001) demonstrated that propagating a constant amount of aggregated information per link leads to cost effective bandwidth sharing. We propose oAIS, a new aggregate information scenario, in which we judiciously select the propagated information, such that the protocol overhead is identical to that of Kodialam and Lakshman. Simulations show that oAIS outperforms other information scenarios with comparable protocol overheads.

RED-BL: Energy solution for loading data centers

Cloud infrastructure providers and data center operators spend a major portion of their operations budget on the electric bills. We present RED-BL (Relocate Energy Demand to Better Locations), a framework for determining an optimal mapping of workload to an existing set of data centers while considering the cost of workload relocation. Within each workload mapping interval, RED-BL solution exploits the geo diversity in electricity price markets. The temporal diversity in those markets is simultaneously exploited by considering a planning window comprising several mapping intervals. Using workload traces from live Internet applications and electricity prices from the US markets, RED-BL can reduce the electric bill by as much as 81% from the case when the workload is equally distributed. Compared to a single data center deployment, an average reduction of 27% in electric bill can be achieved when RED-BL uses 10 or more data centers, a common case for most operators. When compared to existing workload relocation solutions, RED-BL achieves a further reduction of 13.63%, on average. While modest, this reduction can save millions of dollars for the operators. The cost of this saving is an inexpensive computation at the start of each planning window.