Girija J. Narlikar

Coolcams: power-efficient TCAMs for forwarding engines

Ternary content-addressable memories (TCAMs) are becoming very popular for designing high-throughput forwarding engines on routers: they are fast, cost-effective and simple to manage. However, a major drawback of TCAMs is their high power consumption. This paper presents architectures and algorithms for making TCAM-based routing tables more power efficient. The proposed architectures and algorithms are simple to implement, use commodity TCAMs, and provide worst-case power consumption guarantees (independent of routing table contents).

Fast incremental updates for pipelined forwarding engines

Pipelined ASIC architectures are increasingly being used in forwarding engines for high speed IP routers. We explore optimization issues in the design of memory-efficient data structures that support fast incremental updates in such forwarding engines. Our solution aims to balance the memory utilization across the multiple pipeline stages. We also propose a series of optimizations that minimize the disruption to the forwarding process caused by route updates. These optimizations reduce the update overheads by a factor of 2-5 for a variety of different core routing tables and update traces.

Comparing power consumption of an SMT and a CMP DSP for mobile phone workloads

In the DSP world, many media workloads have to perform a specific amount of work in a specific period of time. This observation led us to examine Simultaneous Multithreading (SMT) and Chip Multiprocessing (CMP) for a VLIW DSP architecture (specifically the Star*Core SC140), in conjunction with Frequency/Voltage scaling to decrease dynamic power consumption in next-generation wireless handsets. We study the resulting performance and power characteristics of the two approaches using simulation, compiled code, and realistic workloads that respect real-time constraints. We find that a multithreaded DSP can utilize the available functional units much more efficiently, performing as well as a non-multithreaded DSP but with substantial power savings. Power consumption can also be lowered by using a chip-multiprocessor (CMP) operating at low frequency. We compare the power consumption of an SMT DSP with a CMP DSP under different architectural assumptions; we find that the SMT DSP uses up to 40% less power than the CMP DSP in our target environment.

Robust and Fast Pattern Matching for Intrusion Detection

The rule language of an Intrusion Detection System (IDS) plays a critical role in its effectiveness. A rule language must be expressive, in order to describe attack patterns as precisely as possible. It must also allow for a matching algorithm with predictable and low complexity, in order to ensure robustness against denial-of-service attacks. Unfortunately, these requirements often conflict. We show, for instance, that a single rule, when coupled with a backtracking matching algorithm, can bring the processing rate down to nearly ONE packet per second. Performance vulnerabilities of this type are known for patterns described using regular expressions, and can be avoided by using a deterministic matching algorithm. Increasingly, however, rules are being written using the more powerful regex syntax, which includes non-regular features such as back-references. The matching algorithm for general regexs is based on backtracking, and is thus vulnerable to attacks. The main contribution of this paper is a deterministic algorithm for the full regex syntax, which builds upon the deterministic algorithm for regular expressions. We provide a (rough) complexity bound on the worst-case performance, and show that this bound can be tightened through compile-time analysis of the regex structure. These bounds can be used as an admissibility check, to isolate expressions that require further analysis. Finally, we present an implementation of these algorithms in the context of the Snort IDS, and experimental results on several packet traces which show substantial improvement over the backtracking algorithm.

Protium, an infrastructure for partitioned applications

Remote access feels different from local access. The major issues are consistency (machines vary in GUIs, applications, and devices) and responsiveness (the user must wait for network and server delays), Protium attacks these by partitioning programs into local viewers that connect to remote services using application-specific protocols. Partitioning allows viewers to be customized to adapt to local features and limitations. Services are responsible for maintaining long-term state. Viewers manage the user interface and use state to reduce communication between viewer and service, reducing latency whenever possible. System infrastructure sits between the viewer and service, supporting replication, consistency, session management, and multiple simultaneous viewers. The prototype system includes an editor, a draw program, a PDF viewer, a map database, a music jukebox, and windowing system support. It runs on servers, workstations, PCs, and PDAs under Plan 9, Linux, and Windows; services and viewers have been written in C, Java, and Concurrent ML.

MoneyBee: Towards enabling a ubiquitous, efficient, and easy-to-use mobile crowdsourcing service in the emerging market

We present a mobile crowdsourcing platform called MoneyBee that is accessible to mobile phone users in emerging markets through their mobile operators. The operator has a large subscriber base and the ability to pay task workers using prepaid airtime minutes. These advantages allow MoneyBee to reach far more people than conventional Internet crowdsourcing approaches. The mobile operator already has access to information on user demographics, location and presence, and monthly spending patterns. In addition, the MoneyBee platform gathers user information (such as preferences, skills, and reliability) from a users interaction with the crowdsourcing service. Using this data to intelligently assign crowd-sourcing tasks to relevant workers is a challenging problem. Similarly, efficient dispatching of tasks to minimize the network load on the operator network is equally important. Further, simple interfaces (including speech) are needed to submit as well as execute crowdsourcing tasks on the mobile device. We describe initial solutions to some of these challenges in this paper.

UNAP: User-Centric Network-Aware Push for Mobile Content Delivery

The consumer interest in mobile multimedia content is on the rise, driven by the higher bandwidth of 3G networks and by the availability of low-cost high-resolution mobile devices. However, providing a good user experience remains a challenge due to bandwidth bottlenecks at peak time, channel quality variations and high battery drain incurred by long data transmission times at lower bandwidths. Consequently high jitter, buffering delays and frequent network outages are ever so common for mobile multimedia services. The emerging mobile broadcast networks (e.g. BCMCS, MediaFLO, DVB-H) are well suited for efficient delivery of highly popular content but lack the on-demand, interactive and retransmission (for reliability) capabilities by virtue of being one-way. In addition, due to business reasons (e.g. MediaFLO) or technical reasons (e.g. BCMCS) service providers prefer to deliver only a limited number of popular channels over these networks. In this paper we propose a mobile content delivery architecture that takes wireless specifics into account to enhance the user experience with multimedia services. Our solution makes efficient use of the available bandwidth, does network and channel quality- aware content delivery on the unicast 3G network while at the same time efficiently and reliably schedules content delivery over the mobile broadcast network. In our solution the delivered content is pre-cached on the storage available on the mobile device. This provides a better user experience, reduces the peak load on the network, and reduces the battery drain on the mobile device. Motivated by the proposed architecture we study the problem of scheduling content over a hybrid unicast and broadcast mobile network and design efficient algorithms and heuristics for the problem.

Energy-efficient design and optimization of wireline access networks

Access networks, in particular, Digital Subscriber Line (DSL) equipment, are a significant source of energy consumption for wireline operators. Replacing large monolithic DSLAMs with smaller remote DSLAM units closer to customers can reduce the energy consumption as well as increase the reach of the access network. This paper attempts to formalize the design and optimization of the “last mile” wireline access network with energy as one of the costs to be minimized. In particular, the placement of remote DSLAM units needs to be optimized. We propose solutions for two scenarios. For the scenario where an existing all-copper network from the central office to the customers is to be transformed into a fiber-copper network with remote DSLAM units, we present efficient polynomial-time solutions. For the green-field scenario, where both the access network layout and the placement of remote DSLAM units must be determined, we show that this problem is NP-complete. We present an optimal ILP formulation and also design an efficient heuristic-based approach to build a power and cost optimized access network. Our heuristic-based approach yields results that are very close to optimal. We show how the power consumption of the access network can be reduced by carefully planning the access network and introducing remote DSLAM units.