In the context of IEEE 802.11b network testbeds, we examine the differences between unicast and broadcast link properties, and we show the inherent difficulties in precisely estimating unicast link properties via those of broadcast beacons even if we make the length and transmission rate of beacons be the same as those of data packets. To circumvent the difficulties in link estimation, we propose to estimate unicast link properties directly via data traffic itself without using periodic beacons. To this end, we design a data-driven routing protocol Learn on the Fly (LOF). LOF estimates link quality based on data traffic, and it chooses routes by way of a locally measurable metric ELD, the expected MAC latency per unit-distance to the destination. Using a realistic sensor network traffic trace and an 802.11b testbed of 195 Stargates, we experimentally compare the performance of LOF with that of existing protocols, represented by the geography-unaware ETX and the geography-based PRD. We find that LOF reduces end-to-end MAC latency by a factor of 3 and enhances energy efficiency by a factor up to 2.37, which demonstrate the feasibility as well as potential benefits of datadriven link estimation and routing.

This paper presents a connection handoff interface between the operating system and the network interface. Using this interface, the operating system can offload a subset of TCP connections in the system to the network interface, while the remaining connections are processed on the host CPU. Offloading can reduce computation and memory bandwidth requirements for packet processing on the host CPU. However, full TCP offloading may degrade system performance because finite processing and memory resources on the network interface limit the amount of packet processing and the number of connections. Using handoff, the operating system controls the number of offloaded connections in order to fully utilize the network interface without overloading it. Handoff is transparent to the application, and the operating system may choose to offload connections to the network interface or reclaim them from the interface at any time. A prototype system based on the modified FreeBSD operating system shows that handoff reduces the number of instructions and cache misses on the host CPU. As a result, the number of CPU cycles spent processing each packet decreases by 16–84%. Simulation results show handoff can improve web server throughput (SEPCweb99) by 15%, despite short-lived connections.

In the context of IEEE 802.11b network testbeds, we examine the differences between unicast and broadcast link properties, and we show the inherent difficulties in precisely estimating unicast link properties via those of broadcast beacons even if we make the length and transmission rate of beacons be the same as those of data packets. To circumvent the difficulties in link estimation, we propose to estimate unicast link properties directly via data traffic itself without using periodic beacons. To this end, we design a data-driven routing protocol Learn on the Fly (LOF). LOF chooses routes based on ETX/ETT-type metrics, but the metrics are estimated via MAC feedback for unicast data transmission instead of broadcast beacons. Using a realistic sensor network traffic trace and an 802.11b testbed of ∼195 Stargates, we experimentally compare the performance of LOF with that of beacon-based protocols, represented by the geography-unaware ETX and the geography-based PRD. We find that LOF reduces end-to-end MAC latency by a factor of 3, enhances energy efficiency by a factor up to 2.37, and improves network throughput by a factor up to 7.78, which demonstrate the feasibility and the potential benefits of data-driven link estimation and routing.

In the context of IEEE 802.11b network testbeds, we examine the differences between unicast and broadcast link properties, and we show the inherent difficulties in precisely estimating unicast link properties via those of broadcast beacons even if we make the length and transmission rate of beacons be the same as those of data packets. To circumvent the difficulties in link estimation, we propose to estimate unicast link properties directly via data traffic itself without using beacons. To this end, we design a beacon-free routing protocol Learn on the Fly (LOF). LOF estimates link quality based solely on data traffic, and it chooses routes by way of a locally measurable metric ELD, the expected MAC latency per unit-distance to the destination. Using a realistic sensor network traffic trace and an 802.11b testbed of 195 Stargates, we experimentally compare the performance of LOF with that of existing protocols, represented by the geographyunaware ETX and the geography-based PRD. We find that LOF reduces end-to-end MAC latency by a factor of 3, enhances energy efficiency by a factor up to 2.37, and improves route stability by 2 orders of magnitude. The results demonstrate the feasibility as well as potential benefits of data-driven beacon-free link estimation and routing. —experiment-based design and analysis, bursty convergecast, beacon-free geographic routing, data-driven link quality estimation, MAC latency, IEEE 802.11b, real time, energy, reliability 1

Abstract—Innovative efforts to provide a clean-slate design of congestion control for future high-speed heterogeneous networks have recently led to the development of explicit congestion control. These methods [6], [16], [17], [38] rely on multi-byte router feedback and aim to contribute to the design of a more scalable Internet of tomorrow. However, experimental evaluation and deployment experience with these approaches, especially in highcapacity networks and multi-link settings, is still missing from the literature. This paper aims to fill this void and investigate the behavior of these methods in single and multi-link topologies involving real systems and gigabit networks. We implement four recent protocols XCP [17], JetMax [38], RCP [6], and PIQI-RCP [16] in the existing Linux TCP/IP stack [24] in a manner that is transparent to applications and conduct experiments in Emulab [7] using a variety of network configurations. Our experiments not only confirm the known behavior of these methods, but also demonstrate their previously undocumented properties. I.

Security administrators use network intrusion detection systems (NID systems) as a tool for detecting attacks and misuse, using passive monitoring techniques. However, there are sophisticated attacks which use ambiguities in protocol specifications to subvert detection. In these attacks, the destination endpoint reconstructs a malicious interpretation, whereas the passive NID system’s protocol stack interprets the protocol as a benign exchange. There is a dire need for a new software element at the entry point of the network, which transparently modifies network traffic, so as to remove all possible ambiguities. This will ensure that all internal hosts and the NIDS interpret the traffic in a uniform way, hence removing all chances of an attack sneaking past the NIDS, unnoticed and unmonitored. In this paper, we will present the design and implementation of a normalizer whose job is to eliminate evasion and insertion attacks against an NIDS at the transport and network layers. 1.