Cross-layer wireless bit rate adaptation

This paper presents SoftRate, a wireless bit rate adaptation protocol that is responsive to rapidly varying channel conditions. Unlike previous work that uses either frame receptions or signal-to-noise ratio (SNR) estimates to select bit rates, SoftRate uses confidence information calculated by the physical layer and exported to higher layers via the SoftPHY interface to estimate the prevailing channel bit error rate (BER). Senders use this BER estimate, calculated over each received packet (even when the packet has no bit errors), to pick good bit rates. SoftRate's novel BER computation works across different wireless environments and hardware without requiring any retraining. SoftRate also uses abrupt changes in the BER estimate to identify interference, enabling it to reduce the bit rate only in response to channel errors caused by attenuation or fading. Our experiments conducted using a software radio prototype show that SoftRate achieves 2X higher throughput than popular frame-level protocols such as SampleRate and RRAA. It also achieves 20% more throughput than an SNR-based protocol trained on the operating environment, and up to 4X higher throughput than an untrained SNR-based protocol. The throughput gains using SoftRate stem from its ability to react to channel variations within a single packet-time and its robustness to collision losses.National Science Foundation (U.S.) (Grant CNS-0721702)National Science Foundation (U.S.) (Grant CNS-0520032)Foxconn International Holdings Ltd

Revisiting Internet Adressing: Back to the Future!

IP prefixes undermine three goals of Internet routing: accurate reflection of network-layer reachability, secure routing messages, and effective traffic control. This paper presents Atomic IP (AIP), a simple change to Internet addressing (which in fact reverts to how addressing once worked), that allows Internet routing to achieve these goals

DDoS defense by offense

This article presents the design, implementation, analysis, and experimental evaluation of speak-up, a defense against application-level distributed denial-of-service (DDoS), in which attackers cripple a server by sending legitimate-looking requests that consume computational resources (e.g., CPU cycles, disk). With speak-up, a victimized server encourages all clients, resources permitting, to automatically send higher volumes of traffic. We suppose that attackers are already using most of their upload bandwidth so cannot react to the encouragement. Good clients, however, have spare upload bandwidth so can react to the encouragement with drastically higher volumes of traffic. The intended outcome of this traffic inflation is that the good clients crowd out the bad ones, thereby capturing a much larger fraction of the server's resources than before. We experiment under various conditions and find that speak-up causes the server to spend resources on a group of clients in rough proportion to their aggregate upload bandwidths, which is the intended result.National Science Foundation (U.S.) (NSF grant CNS-0225660)National Science Foundation (U.S.) (NSF grant CNS-0520241)United States. Dept. of Defense (National Security Science and Engineering Faculty Fellowship

Harnessing Exposed Terminals in Wireless Networks

This paper presents the design, implementation, and experimental evaluation of CMAP (Conflict Maps), a system that increases the number of successful concurrent transmissions in a wireless network, achieving higher aggregate throughput compared to networks that use carrier sense multiple access (CSMA). CMAP correctly identifies and exploits exposed terminals in which two senders are within range of one another, but each intended receiver is far enough from the other sender that the two transmissions can succeed even if done concurrently. CMAP includes a reactive channel access scheme in which nodes transmit concurrently (even if there’s the possibility of a collision), then observe the loss probability to determine whether they are better off transmitting concurrently or not. Experimental results from a 50-node 802.11a testbed show that CMAP improves throughput by 2 × over CSMA with exposed terminals, while converging to the performance of CSMA when the senders and receivers are all close to each other. CMAP also improves throughput by up to 47 % over CSMA in realistic access point-based networks by exploiting concurrent transmission opportunities.

Cross-layer wireless bit rate adaptation.

ABSTRACT This paper presents SoftRate, a wireless bit rate adaptation protocol that is responsive to rapidly varying channel conditions. Unlike previous work that uses either frame receptions or signal-to-noise ratio (SNR) estimates to select bit rates, SoftRate uses confidence information calculated by the physical layer and exported to higher layers via the SoftPHY interface to estimate the prevailing channel bit error rate (BER). Senders use this BER estimate, calculated over each received packet (even when the packet has no bit errors), to pick good bit rates. SoftRate's novel BER computation works across different wireless environments and hardware without requiring any retraining. SoftRate also uses abrupt changes in the BER estimate to identify interference, enabling it to reduce the bit rate only in response to channel errors caused by attenuation or fading. Our experiments conducted using a software radio prototype show that SoftRate achieves 2× higher throughput than popular frame-level protocols such as SampleRat

Mixture of betel leaf, areca nut and tobacco chewing is a risk factor for cytogenetic damage in construction workers from south India

Aim: To determine the cytogenetic effect of betel leaf, areca nut and tobacco mixture usage among female construction workers in Tamilnadu, Southern India. Methods: Totally 236 buccal cells and blood samples were collected from 80 betel quid users and 76 users with tobacco snuffing habit which were compared with 80 healthy subjects. Peripheral blood leukocyte cultures were analyzed for chromosomal aberrations (CA) and exfoliated cells from the buccal mucosa were examined for micronucleus (MN). Results: Statistically significant (p<0.01) increase in CA and MN were observed in users with snuffing habit when compared to users without snuffing habit and controls as confirmed by chi-square test. Therefore, specific biomarkers on cytogenetic endpoints might help in planning precautionary measures to reduce oral cancer risks. Conclusions: The present study can be concluded that a mixture of betel quid, areca nut and tobacco chewing/snuffing is unsafe for oral health. The genotoxic effect of smokeless tobacco should be considered in addition to other known hazards for assessing health risks