1,911 research outputs found
Minimally-intrusive frequent round trip time measurements using Synthetic Packet-Pairs
Accurate and frequent round trip time (RTT) measurements are important in testbeds and operational networks. Active measurement techniques inject probe packets that may modify the behaviour of the observed network and may produce misleading RTT estimates if the network handles probe packets differently to regular packets. Previous passive measurement techniques address these issues, but require precise time synchronisation or are limited to certain traffic types. We introduce Synthetic Packet-Pairs (SPP), a novel passive technique for RTT measurement. SPP provides frequently updated RTT measurements using any network traffic already present in the network without the need for time synchronisation. SPP accurately measures the RTT experienced by any application's traffic, even applications that do not exhibit symmetric client-server packet exchanges. We experimentally demonstrate the advantages of SPP
Estimating IPv4 address space usage with capture-recapture
As of April 2013 almost 95% of the IPv4 address space has been allocated. Yet, the transition to IPv6 is still relatively slow. One reason could be existing âIPv4 reservesâ â allocated but unused IPv4 addresses. Knowing how many addresses are actively used is important to predict a potential IPv4 address market, predict the IPv6 deployment time frame, and measure progressive exhaustion after the IPv4 space is fully allocated. Unfortunately, only a fraction of hosts respond to active probes, such as âpingâ. We propose a capture-recapture method to estimate the actively used IPv4 addresses from multiple incomplete data sources, including âpingâ censuses, network traces and server logs. We estimate that at least 950â1090 million IPv4 addresses are used, which is 36â41% of the publicly routed space. We analyse how the utilisation depends on various factors, such as region, country and allocation prefix length
Dynamics of the IP time to live field in internet traffic flows
The Time To Live (TTL) field present in the IP protocol header is used to limit the lifetime of packets in the network. Previous research has measured TTL for studying path lengths and dynamics in IP networks, and for detecting route changes. How the TTL varies over short timescales of subsequent packets of traffic flows has not yet been analysed. Such knowledge is needed for passively detecting route changes based on existing traffic in the network or traffic traces, and for designing mechanisms that modulate the TTL field such as IP traceback techniques and covert channels. In this paper we analyse small time scale TTL variation in Internet traffic flows based on a number of packet traces captured at different locations in the Internet
Client RTT and hop Count Distributions viewed from an Australian âEnemy Territoryâ Server
Network game servers experience traffic caused by actual game players and by remote clients simply probing the game serverâs current status. Game clients probe game servers for information such as the current map and number of current players on the server to enable players to fin d suitable games. The number of clients that probe a given server is orders of magnitudes higher than the number of eventual players. Network level round trip time (delay, or âla gâ) between a client and server is a very important criterion for players when deciding which server to join. Often the round trip time is roughly proportional to hop count. In this paper we document and investigate the distributions of round trip time and hop count for game clients that only probe and clients that actually play on a public game server. We also examine the geographical distributions of both groups. Our data was gathered from a Wolfenstein Enemy Territory server operating in Melbourne, Australia, in late 2004
Mitigating sampling error when measuring internet client IPv6 capabilities
Despite the predicted exhaustion of unallocated IPv4 addresses be- tween 2012 and 2014, it remains unclear how many current clients can use its successor, IPv6, to access the Internet. We propose a refinement of previous measurement studies that mitigates intrin- sic measurement biases, and demonstrate a novel web-based tech- nique using Google ads to perform IPv6 capability testing on a wider range of clients. After applying our sampling error reduction, we find that 6% of world-wide connections are from IPv6-capable clients, but only 1â2% of connections preferred IPv6 in dual-stack (dual-stack failure rates less than 1%). Except for an uptick around IPv6-day 2011 these proportions were relatively constant, while the percentage of connections with IPv6-capable DNS resolvers has in- creased to nearly 60%. The percentage of connections from clients with native IPv6 using happy eyeballs has risen to over 20
Quantitative anomalous powder diffraction analysis of cation disorder in kesterite semiconductors
Kesterite type compound semiconductors, containing copper and zinc, have photovoltaic properties depending on cation distribution in the crystal structure. Anomalous diffraction allows discrimination of isoelectronic cations, in principle allowing a straightforward determination of site occupation factors from data collected at multiple energies close to the X ray absorption edges of copper and zinc. However, extremely strong correlation between structural parameters precludes this. We present a recipe based on the direct dependency between refined occupation factors and atomic scattering power, which allows to lift the correlations and to detect issues of individual diffraction patterns or assumptions in the model, thereby allowing for reliable quantitative analysis of the Cu Zn distributio
An essential role of acetylcholine-glutamate synergy at habenular synapses in nicotine dependence
A great deal of interest has been focused recently on the habenula and its critical role in aversion, negative-reward and drug dependence. Using a conditional mouse model of the ACh-synthesizing enzyme choline acetyltransferase (Chat), we report that local elimination of acetylcholine (ACh) in medial habenula (MHb) neurons alters glutamate corelease and presynaptic facilitation. Electron microscopy and immuno-isolation analyses revealed colocalization of ACh and glutamate vesicular transporters in synaptic vesicles (SVs) in the central IPN. Glutamate reuptake in SVs prepared from the IPN was increased by ACh, indicating vesicular synergy. Mice lacking CHAT in habenular neurons were insensitive to nicotine-conditioned reward and withdrawal. These data demonstrate that ACh controls the quantal size and release frequency of glutamate at habenular synapses, and suggest that the synergistic functions of ACh and glutamate may be generally important for modulation of cholinergic circuit function and behavior
Multi-Qubit Systems: Highly Entangled States and Entanglement Distribution
A comparison is made of various searching procedures, based upon different
entanglement measures or entanglement indicators, for highly entangled
multi-qubits states. In particular, our present results are compared with those
recently reported by Brown et al. [J. Phys. A: Math. Gen. 38 (2005) 1119]. The
statistical distribution of entanglement values for the aforementioned
multi-qubit systems is also explored.Comment: 24 pages, 3 figure
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