Discovering Network Neighborhoods Using Peer-to-Peer Lookups

In many distributed applications, end hosts need to know the network locations of other nearby participating hosts in order to enhance overall performance. Potential applications that can benefit from the location information include automatic selection of nearby Web servers, proximity routing in a peer-to-peer system, and loss recovery in reliable multicasting. We focus in this paper on the network neighborhood discovery problem in large-scale distributed systems. In these systems, the number of participating nodes can be very large, and the membership can dynamically change. Our goal is for each node to discover other "nearby" participating nodes in a completely decentralized manner, where each node probes only a small subset of other nodes in the system. This approach will lead to improved overall performance by matching client requests for services with participants in the peer-to-peer service system that are, on average, nearby in the network sense. Recent works in distributed peer-to-peer systems, such as Chord, CAN, Tapestry and Pastry, provide efficient distributed lookup structures. In this paper, we investigate a rendezvous-based scheme for a node to discover other nearby participating nodes using a peer-to-peer lookup system such as Chord. Given a key, the Chord protocol maps the key onto a node. Our idea for network neighborhood discovery is for each host to compute a key that characterizes its network location on the Internet. We call such a key the location key, and the nodes that these location keys are mapped to the Rendezvous Points. To lookup other nearby participating nodes, a node seeking some service queries its corresponding rendezvous point using its location key. We focus on the issue of how to generate the location key in a distributed fashion such that nodes that are close to each other in the actual network will have similar location key values, and therefore be mapped to nearby locations on the Chord ring. In this paper, we examine the performance tradeoffs of such a rendezvous scheme using the Global Network Positioning (GNP) approach to generate the location keys. In GNP, each node measures its network distances to a few landmark nodes to derive its coordinates in a D-dimensional geometric space. We generate a host's Chord location key from its 1-dimensional GNP coordinate, and use coordinates from a higher dimensional space to refine the searching process for the closest node. We evaluate our scheme in the context of the nearest neighbor discovery problem. Using data from the Active Measurement Project of the National Laboratory for Applied Network Research (NLANR), we compare its performance with a random mapping scheme, where location keys are randomly generated. Using our coordinate-based rendezvous scheme, 66% of the nodes found their actual closest network neighbor by pinging only a small number of nodes.Singapore-MIT Alliance (SMA

PALM: Predicting Internet Network Distances Using Peer-to-Peer Measurements

Landmark-based architecture has been commonly adopted in the networking community as a mechanism to measure and characterize a host's location on the Internet. In most existing landmark based approaches, end hosts use the distance measurements to a common, fixed set of landmarks to derive an estimated location on the Internet. This paper investigates whether it is possible for participating peer nodes in an overlay network to collaboratively construct an accurate geometric model of its topology in a completely decentralized peer-to-peer fashion, without using a fixed set of landmarks. We call such a peer-to-peer approach in topology discovery and modeling using landmarks PALM (Peers As LandMarks). We evaluate the performance characteristics of such a decentralized coordinates-based approach under several factors, including dimensionality of the geometric space, peer distance distribution, and the number of peer-to-peer distance measurements used. We evaluate two PALM-based schemes: RAND-PALM and ISLAND. In RAND-PALM, a peer node randomly selects from existing peer nodes as its landmarks. In ISLAND (Intelligent Selection of Landmarks), each peer node selects its landmarks by exploiting the topological information derived based on existing peer nodes' coordinates values.Singapore-MIT Alliance (SMA

Hamming Teaching Award, Heather Gregg, 2017

Richard W. Hamming Annual Faculty Award for Achievement in Teachin

NPS Distinguished Professor Awardees, 2018

Distinguished Professor Award. Recipients Professor John Arquilla, DA, Professor Moshe Kress, OR, Professor John C. McEachen, ECE, Professor Clifford A. Whitcomb, S

NPS Distinguished Professor Awardee, 2019

Distinguished Professor Award. Recipient Professor Phillip E. Pace, EC

A Decentralized Network Coordinate System for Robust Internet Distance

Network distance, measured as round-trip latency be-tween hosts, is important for the performance of many In-ternet applications. For example, nearest server selection and proximity routing in peer-to-peer networks rely on the ability to select nodes based on inter-host latencies. This paper presents PCoord, a decentralized network coordi-nate system for Internet distance prediction. In PCoord, the network is modeled as a D-dimensional geometric space; each host computes its coordinates in this geometric space to characterize its network location based on a small num-ber of peer-to-peer network measurements. The goal is to embed hosts in the geometric space so that the Euclidean distance between two hosts ’ coordinates accurately predicts their actual inter-host network latency. PCoord constructs network coordinates in a fully decentralized fashion. We present several mechanisms in PCoord to stabilize the sys-tem convergence. Our simulation results using real Internet measurements suggest that, even under an extremely chal-lenging flash-crowd scenario where 1740 hosts simultane-ously join the system, PCoord with a 5-dimensional Eu-clidean model is able to converge to 11 % median prediction error in 10 coordinate updates per host on average.

976-14 Immediate Heart Rate Response to Orthostatic Stress During β-blocker Therapy for Vasodepressor Syncope

Although β-blockers are preferred agents for therapy of vasodepressor syncope (VDS), they are not uniformly effective and their mechanism of action is incompletely understood. Since we have previously shown a differential therapeutic response to β-blocker therapy between pts with isoproterenol-independent [iso(-)] and isoproterenol-dependent [iso(+)] VDS during tilt table testing we sought to determine whether this was due to a differential heart rate (HR) response to orthostasis during β-blockade. We therefore examined immediate HR and blood pressure responses to upright tilt before and after initiation of therapy with atenolol (12.5–50mg daily) in 62 pts with VDS and positive tilt tests. The protocol comprised upright tilt (60°) for up to 60min followed by repeat tilt for 15min during isoproterenol (iso) infusion. Supine HR, mean arterial pressure (MAP) and pulse pressure (PP) were determined as the mean of 3 consecutive 1-min samples during supine rest; orthostatic HR, MAP, and PP were the mean of the samples recorded in the first 3min after upright tilt (before infusion of iso). Response to atenolol required completion of tilt with and without infusion of iso. There were 15 iso(-) pts and 47 iso(+) pts. The groups did not differ significantly in blood pressure response (MAP, PP) to orthostasis. Supine HR fell and the ΔHR in response to orthostasis was blunted during therapy in both groups:Baseline (Mean ± SD)Rx (Mean ± SD)Iso(+)Iso(-)pIso(+)Iso(-)pSupine HR69±1368±9NS57±958±8NSOrthostatic ΔHR8±712±9NS3±53±4NS11 iso(-) pts (73%) had a therapeutic response to β-blockade compared with 46 iso(+) pts (98%, p=0.01); the orthostatic ΔHR in the iso(-) pts who failed β-blocker therapy was no different from the response in the patients with a therapeutic response.ConclusionsThe HR response to orthostasis is comparably blunted after β-blockade in pts with iso(-) and iso(+) VDS, indicating that failure to respond is not due to inadequate β-blockade and suggests that in some pts iso-independent VDS may be independent of a cardiac β1 receptor mediated mechanism