Chung–Horng Lung

Hassan Halabian, Ioannis Lambadaris, Chung-Horng Lung

In this paper, we characterize the network stability region (capacity region) of multi-queue multi-server (MQMS) queueing systems with stationary channel distribution and stationary arrival processes. The stability region is specified by a finite set of linear inequalities. We first show that the stability region is a polytope characterized by the finite set of its facet defining hyperplanes. We explicitly determine the coefficients of the linear inequalities describing the facet defining hyperplanes of the stability region polytope. We further derive the necessary and sufficient conditions for the stability of the system for general arrival processes with finite first and second moments. For the case of stationary arrival processes, the derived conditions characterize the system stability region. Furthermore, we obtain an upper bound for the average queueing delay of Maximum Weight (MW) server allocation policy which has been shown in the literature to be a throughput optimal policy for MQMS systems. Using a similar approach, we can characterize the stability region for a fluid model MQMS system. However, the stability region of the fluid model system is described by an infinite number of linear inequalities since in this case the stability region is a convex surface. We present an example where we show that in some cases depending on the channel distribution, the stability region can be characterized by a finite set of non-linear inequalities instead of an infinite number of linear inequalities.

Hassan Halabian, Ioannis Lambadaris, Chung-Horng Lung

In this paper, we characterize the stability region of multi-queue multi-server (MQMS) queueing systems with stationary channel and packet arrival processes. Toward this, the necessary and sufficient conditions for the stability of the system are derived under general arrival processes with finite first and second moments. We show that when the arrival processes are stationary, the stability region form is a polytope for which we explicitly find the coefficients of the linear inequalities which characterize the stability region polytope.

Ziqiang Wang, Changcheng Huang, Chung-Horng Lung

In large-model distributed training, especially large language model workloads, gradient All-Reduce increasingly stresses the memory and communication path. This paper asks whether a Compute Express Link (CXL) memory controller can aggregate low-bit gradient signals as gradient cache lines pass through it, while preserving a 32-bit floating-point (FP32) path for workloads, layers, or phases that should not use low-bit approximation. We present NEURON-Fabric, a CXL-side controller architecture that performs packed gradient-binary (G-Binary) sign-count aggregation and gradient-ternary (G-Ternary) gated aggregation near CXL memory, with a control interface for selecting low-bit or FP32 paths. Cycle-level timing experiments show that the measured five-cycle low-bit aggregation datapath adds at most 1.67 percent exposed runtime overhead in the full last-level-cache miss regime; under bandwidth pressure, the same compute stage is hidden by CXL service time. Functional tests confirm byte-exact identity read-back, G-Binary sign-count aggregation, and G-Ternary gating. Training checks quantify the communication and accuracy tradeoff: low-bit aggregation remains close to FP32 on CIFAR-10/ResNet-18 and SST-2/DistilBERT, while full-path low-bit aggregation fails on CIFAR-100/ResNet-18. Layer-aware admission identifies the classifier head as sensitive; keeping the head on FP32 while applying low-bit aggregation to the backbone recovers most accuracy and reduces gradient traffic to 3.6-5.4 percent of the FP32 baseline. Hardware synthesis and FPGA place-and-route estimates suggest that the 512-bit aggregation datapath is small enough to be treated as a near-memory datapath extension rather than a separate accelerator-scale block.

Ahmed Raoof, Chung-Horng Lung, Ashraf Matrawy

The IPv6 over Low-powered Wireless Personal Area Network (6LoWPAN) protocol was introduced to allow the transmission of Internet Protocol version 6 (IPv6) packets using the smaller-size frames of the IEEE 802.15.4 standard, which is used in many Internet of Things (IoT) networks. The primary duty of the 6LoWPAN protocol is packet fragmentation and reassembly. However, the protocol standard currently does not include any security measures, not even authenticating the fragments immediate sender. This lack of immediate-sender authentication opens the door for adversaries to launch several attacks on the fragmentation process, such as the buffer-reservation attacks that lead to a Denial of Service (DoS) attack and resource exhaustion of the victim nodes. This paper proposes a security integration between 6LoWPAN and the Routing Protocol for Low Power and Lossy Networks (RPL) through the Chained Secure Mode (CSM) framework as a possible solution. Since the CSM framework provides a mean of immediate-sender trust, through the use of Network Coding (NC), and an integration interface for the other protocols (or mechanisms) to use this trust to build security decisions, 6LoWPAN can use this integration to build a chain-of-trust along the fragments routing path. A proof-of-concept implementation was done in Contiki Operating System (OS), and its security and performance were evaluated against an external adversary launching a buffer-reservation attack. The results from the evaluation showed significant mitigation of the attack with almost no increase in power consumption, which presents the great potential for such integration to secure the forwarding process at the 6LoWPAN Adaptation Layer

Ahmed Raoof, Chung-Horng Lung, Ashraf Matrawy

As the de facto routing protocol for many Internet of Things (IoT) networks nowadays, and to assure the confidentiality and integrity of its control messages, the Routing Protocol for Low Power and Lossy Networks (RPL) incorporates three modes of security: the Unsecured Mode (UM), Preinstalled Secure Mode (PSM), and the Authenticated Secure Mode (ASM). While the PSM and ASM are intended to protect against external routing attacks and some replay attacks (through an optional replay protection mechanism), recent research showed that RPL in PSM is still vulnerable to many routing attacks, both internal and external. In this paper, we propose a novel secure mode for RPL, the Chained Secure Mode (CSM), based on the concept of intraflow Network Coding (NC). The CSM is designed to enhance RPL resilience and mitigation capability against replay attacks while allowing the integration with external security measures such as Intrusion Detection Systems (IDSs). The security and performance of the proposed CSM were evaluated and compared against RPL in UM and PSM (with and without the optional replay protection) under several routing attacks: the Neighbor attack (NA), Wormhole (WH), and CloneID attack (CA), using average packet delivery rate (PDR), End-to-End (E2E) latency, and power consumption as metrics. It showed that CSM has better performance and more enhanced security than both the UM and PSM with the replay protection, while mitigating both the NA and WH attacks and significantly reducing the effect of the CA in the investigated scenarios.

Ahmed Raoof, Chung-Horng Lung, Ashraf Matrawy

The current standard of Routing Protocol for Low Power and Lossy Networks (RPL) incorporates three modes of security: the Unsecured Mode (UM), Preinstalled Secure Mode (PSM), and the Authenticated Secure Mode (ASM). While the PSM and ASM are intended to protect against external routing attacks and some replay attacks (through an optional replay protection mechanism), recent research showed that RPL in PSM is still vulnerable to many routing attacks, both internal and external. In this paper, we propose a novel secure mode for RPL, the Chained Secure Mode (CSM), based on the concept of intraflow Network Coding. The main goal of CSM is to enhance RPL resilience against replay attacks, with the ability to mitigate some of them. The security and performance of a proof-of-concept prototype of CSM were evaluated and compared against RPL in UM and PSM (with and without the optional replay protection) in the presence of Neighbor attack as an example. It showed that CSM has better performance and more enhanced security compared to both the UM and PSM with the replay protection. On the other hand, it showed a need for a proper recovery mechanism for the case of losing a control message.

Ahmed Raoof, Ashraf Matrawy, Chung-Horng Lung

As the Routing Protocol for Low Power and Lossy Networks (RPL) became the standard for routing in the Internet of Things (IoT) networks, many researchers had investigated the security aspects of this protocol. However, no work (to the best of our knowledge) has investigated the use of the security mechanisms included in the protocol standard, due to the fact that there was no implementation for these features in any IoT operating system yet. A partial implementation of RPL security mechanisms was presented recently for Contiki operating system (by Perazzo et al.), which provided us with the opportunity to examine RPL security mechanisms. In this paper, we investigate the effects and challenges of using RPL security mechanisms under common routing attacks. First, a comparison of RPL performance, with and without its security mechanisms, under three routing attacks (Blackhole, Selective- Forward, and Neighbor attacks) is conducted using several metrics (e.g., average data packet delivery rate, average data packet delay, average power consumption... etc.) Based on the observations from this comparison, we came with few suggestions that could reduce the effects of such attacks, without having added security mechanisms for RPL.