33 research outputs found
Observation-based Cooperation Enforcement in Ad Hoc Networks
Ad hoc networks rely on the cooperation of the nodes participating in the
network to forward packets for each other. A node may decide not to cooperate
to save its resources while still using the network to relay its traffic. If
too many nodes exhibit this behavior, network performance degrades and
cooperating nodes may find themselves unfairly loaded. Most previous efforts to
counter this behavior have relied on further cooperation between nodes to
exchange reputation information about other nodes. If a node observes another
node not participating correctly, it reports this observation to other nodes
who then take action to avoid being affected and potentially punish the bad
node by refusing to forward its traffic. Unfortunately, such second-hand
reputation information is subject to false accusations and requires maintaining
trust relationships with other nodes. The objective of OCEAN is to avoid this
trust-management machinery and see how far we can get simply by using direct
first-hand observations of other nodes' behavior. We find that, in many
scenarios, OCEAN can do as well as, or even better than, schemes requiring
second-hand reputation exchanges. This encouraging result could possibly help
obviate solutions requiring trust-management for some contexts.Comment: 10 pages, 7 figure
Building Resilient Cloud Over Unreliable Commodity Infrastructure
Cloud Computing has emerged as a successful computing paradigm for
efficiently utilizing managed compute infrastructure such as high speed
rack-mounted servers, connected with high speed networking, and reliable
storage. Usually such infrastructure is dedicated, physically secured and has
reliable power and networking infrastructure. However, much of our idle compute
capacity is present in unmanaged infrastructure like idle desktops, lab
machines, physically distant server machines, and laptops. We present a scheme
to utilize this idle compute capacity on a best-effort basis and provide high
availability even in face of failure of individual components or facilities.
We run virtual machines on the commodity infrastructure and present a cloud
interface to our end users. The primary challenge is to maintain availability
in the presence of node failures, network failures, and power failures. We run
multiple copies of a Virtual Machine (VM) redundantly on geographically
dispersed physical machines to achieve availability. If one of the running
copies of a VM fails, we seamlessly switchover to another running copy. We use
Virtual Machine Record/Replay capability to implement this redundancy and
switchover. In current progress, we have implemented VM Record/Replay for
uniprocessor machines over Linux/KVM and are currently working on VM
Record/Replay on shared-memory multiprocessor machines. We report initial
experimental results based on our implementation.Comment: Oral presentation at IEEE "Cloud Computing for Emerging Markets",
Oct. 11-12, 2012, Bangalore, Indi
The Capacity of Multi-Hop Wireless Networks with TCP Regulated Traffic
We study the capacity of multi-hop wireless networks with TCP regulated traffic. We study the dependence of the capacity on the transmission range of nodes in the network. Specifically, we examine the sensitivity of the capacity to the speed of the nodes and the number of TCP connections in an ad hoc network. By incorporating the notion of a minimal acceptable QoS metric (loss) for an individual session, we argue that the QoS-aware capacity is a more accurate model of the TCP-centric capacity of an ad-hoc network. We study the dependence of capacity on the source application (Telnet or FTP) and on the choice of the ad-hoc routing protocol (AODV, DSR or DSDV). We conclude that persistent and non-persistent traffic behave quite differently in an ad-hoc network
MACA-P: A MAC for Concurrent Transmissions in Multi-hop Wireless Networks
Abstract: This paper presents the initial design and performance study of MACA-P, a RTS/CTS based MAC protocol that enables simultaneous transmissions in multihop ad-hoc wireless networks. Providing such low-cost multihop and high performance wireless access networks is an important enabler of pervasive computing. MACA-P is a set of enhancements to the 802.11 DCF that allows parallel transmissions in many situations when two neighboring nodes are either both receivers or both transmitters, but a receiver and a transmitter are not neighbors. Like 802.11, MACA-P contains a contention-based reservation phase prior to data transmission. However, the data transmission is delayed by a control phase interval, which allows multiple sender-receiver pairs to synchronize their data transfers, thereby avoiding collisions and improving system throughput. II. I
High-performance architectures for IP-based multihop 802.11 networks
The concept of a forwarding node, which receives packets from upstream nodes and then transmits these packets to downstream nodes, is a key element of any multi-hop network, wired or wireless. While high-speed IP router architectures have been extensively studied for wired networks, the concept of a “wireless IP router ” has not been addressed so far. In this paper, we examine the limitations of the IEEE 802.11 MAC protocol in supporting a low-latency and high-throughput IP datapath comprising multiple wireless LAN hops. We first propose a wireless IP forwarding architecture that uses MPLS with modifications to the 802.11 MAC to significantly improve the packet forwarding efficiency. We then study further enhancements to the 802.11 MAC that improve the system throughput by allowing a larger number of concurrent packet transmissions in multi-hop 802.11-based IP networks. With 802.11 poised to be the dominant technology for wireless LANs, we believe a combined approach to MAC, packet forwarding and transport layer protocols is needed to make highperformance multi-hop 802.11 networks practically viable. 1