Wireless Networks
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ItemA Network Testbed for Ad-Hoc Communications using Raspberry Pi and 802.11( 2019-01-08)We have built a testbed ad-hoc wireless network to evaluate the AllNet ad-hoc networking protocol. The testbed currently consists of 4 Raspberry Pi Zero W embedded systems and a linux laptop, all using 802.11/WiFi ad-hoc (IBSS) mode. The embedded systems are placed in a line such that each is only able to reliably communicate with one system before it and one system after it in line. The testbed displays phenomena that are observed in real life, including: - greater delay to reach devices that are farther away - variability in the round-trip time to each device - the current version of the AllNet protocol (AllNet~3.2) successfully prioritizes messages. In particular, trace messages, which are sent with least priority, are rarely delivered if mainstream data traffic from the AllNet network is allowed onto the testbed. - system connectivity varies over time, sometimes allowing direct links between systems that are normally unable to communicate The paper includes practical considerations of testbed deployment using the Raspberry Pi, and an analysis of the performance of the AllNet protocol that is driving improvements in the design and implementation.
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ItemPerformance of Real-TimeWireless Communication for Railway Environments with IEEE 802.11p( 2019-01-08)IEEE 802.11p complements the widespread 802.11 standard for use in vehicular environments. Designed for communication between wireless devices in rapidly changing environments, it handles situations where connection and communication must be completed in very short periods of time. Even though this is supposed to be a substantial improvement and essential for real-time applications, latencies have been rarely investigated in existing studies. Based on practical experiments, we evaluate how beneficial 802.11p’s changes in comparison to regular 802.11n are and whether the usage of IEEE 802.11p is suitable within environments with real-time constraints. We compare latencies of networks in OCB mode to both networks in IBSS (ad-hoc) and BSS/AP (access point) mode by measuring the initial connection speed and the latency of ICMP packets’ round-trip times. Furthermore, the response of the latter to disturbances is measured. The results show OCB to be superior to both BSS/AP and IBSS modes in average latency, maximum latency, and standard deviation under all tested circumstances.
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ItemNetwork-Wide Measurement of GPRS Bandwidth and Latency( 2019-01-08)Complementing a recently collected large data set on the TCP connection termination latency in GPRS networks we analyze server-side log data generated in a large scale automatic toll system to observe the network bandwidth. After a recent architectural change the on-board units (OBUs) record GPS tracks and transmit track data to the central system for processing rather than transmitting the toll data after local processing. The bandwidth in upload direction is estimated from the server-side log entries and corrected for the network latency. The data collected allows comparing the performance of seven types of OBUs in three GPRS networks over time. While the three networks differ in the average bandwidth offered, the biggest performance impact is the OBU type where modems with the same specification yield different upload rates. In addition we update the GPRS network latency data by fitting two statistical distributions, improving markedly on the prior results.
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ItemA Novel Denial of Service Vulnerability in Long Term Evolution Cellular Networks( 2019-01-08)Currently many cellular networks operate using the Long Term Evolution (LTE) protocol. Therefore, most mobile subscribers interact with LTE on a daily basis, and thus are affected by the security standards and mechanisms it implements. Here, we propose a vulnerability within the LTE protocol: the mobility management control signaling, which dictates how a user equipment (UE) synchronizes with an enhanced Node-B (eNodeB) to prevent intersymbol interference. Presented are the implications and the overall effects on the bit error rate (BER) of falsified signaling which forces a UE to incorrectly advance or delay its uplink timing. Specifically, we derive a lower bound on the BER for UE that is subjected to the aforementioned signaling. Our simulation results show that a non-zero BER can be guaranteed regardless of noise conditions. Finally, we propose encryption of this signaling to prevent such an attack.
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ItemIntroduction to the Minitrack on Wireless Networks( 2019-01-08)