Search

WiFi 6 based on the IEEE 802.11ax amendment is intended to improve spectral efficiency and area throughput operations in high density environments. This is achieved (among other methods) by the introduction of Orthogonal Frequency Division Multiple Access (OFDMA) and enhanced multi-user Multiple Input Multiple Output (MU-MIMO) features. In this work, we explore the performance of downlink and uplink OFDMA in 802.11ax via extensive simulation based evaluation (latency, throughput, range) compared to conventional single user (SU) transmissions. Based on our results, we conclude that OFDMA can reduce the median latency from ∼5 ms to less than 1 ms in non-saturation conditions. When used in conjunction with efficient multi-user buffer status report and restricted EDCA mechanisms, OFDMA can increase the saturation throughput by more than 10 percent. Moreover, UL OFDMA also improves aggregate throughput at longer ranges due to the narrower sub-channels (equivalently increased transmit power spectral density); four stations achieve an aggregate throughput 35 percent higher than a station transmitting SU frames and located at a range 1.5 times closer to the access point.

The Software Defined Network (SDN) paradigm represents a major breakthrough in the networking field, due to its unprecedented capabilities in terms of flexibility and programmability. SDNs have been successfully deployed in data centers and small to medium enterprises. However, adopting the SDN paradigm in the context of wide area networks is more challenging, due to a number of factors including the higher probability that node and link failures occur and the unavailability of a dedicated control channel. In this paper, we present a DAG (Directed Acyclic Graph) based forwarding paradigm addressing the challenges that arise when the SDN concept is applied to large scale networks. Specifically, the proposed paradigm aims to limit the number of entries required on the SDN switches, to provide a fast local restoration of single node/link failures without the intervention of the SDN controller and to prevent the possibility of having inconsistent forwarding tables during updates. The proposed paradigm does not require any extension to the OpenFlow protocol and we show how it can be implemented by only using standard features. The DAG-based forwarding paradigm requires to compute a DAG between every pair of ingress-egress switches and to design an index-based hashing scheme to balance the load across the paths in the DAG while avoiding TCP reordering issues. In this paper, we present heuristic algorithms providing a solution to such problems and report the results of a simulation study conducted to assess the performance of the proposed forwarding paradigm.

Comunicació presentada a 2022 IEEE 19th Annual Consumer Communications & Networking Conference (CCNC), celebrat del 8 a l'11 de gener de 2022 de manera virtual. IEEE 802.11be networks (aka Wi-Fi 7) will have to cope with new bandwidth-hungry and low-latency services such as eXtended Reality and multi-party cloud gaming. With this goal in mind, transmit opportunity (TXOP) sharing between coordinated access points (APs) may contribute to alleviating inter-AP contention, hence increasing the overall network throughput. This paper evaluates two coordinated TXOP sharing strategies: coordinated time division multiple access (c-TDMA) and coordinatedTDMA with spatial reuse (c-TDMA/SR). We show that, while c-TDMA alone does not result in any significant improvement in terms of the WLAN throughput, it lays the groundwork to implement coordinated SR (c-SR) techniques. To evaluate the performance of c-TDMA/SR, we propose a fair scheduler able to select the best subset of parallel transmissions in WLAN deployments, as well as the appropriate power levels to be used by APs and stations (STAs), leading to maximum performance. The results obtained for c-TDMA/SR show significant throughput gains compared with c-TDMA, with values higher than 140% in 90% of the considered scenarios. The work of D. Nuñez and B. Bellalta was supported by WINDMAL PGC2018-099959-B-I00 (MCIU/AEI/FEDER,UE) and Cisco.

Researchers from academia, industry and research centers often resort to emulation to overcome the drawbacks associated with network simulation and experimental evaluation. Emulation is broadly classified in environment emulation, usually carried out by running real code in Virtual Machines (VMs) or containers, and network emulation, typically involving network simulators that exchange packets with the real world. In this paper, we focus on network emulation, which is often exploited for rapid prototyping and testing of network protocols and algorithms. We identify the limitations of the approach currently used by various network simulators to provide network emulation and design an alternative solution based on netmap, a framework for high speed packet I/O which is available on multiple operating systems. We argue that the proposed solution to network emulation provides extremely accurate results in terms of packet latency and packet drops and prove our claim by means of an extensive experimental campaign. We also show that by building upon an accurate network emulation mechanism it is possible to validate the implementation of protocols found in network simulators against their implementation in real network stacks. As an example, we present the results of the experiments we conducted to validate the ns-3 implementation of various packet schedulers against their Linux counterpart.

The introduction of Orthogonal Frequency Division Multiple Access (OFDMA) in 802.11ax signifies a change in role for the Access Point (AP) in WiFi networks, with the opportunity to implement more complex scheduling logic to handle Downlink (DL) traffic flows and simultaneously act as coordinator of Multi User (MU) Uplink (UL) transmissions. In this context it becomes necessary to develop reliable network analysis and simulation tools that allow for an in-depth analysis of the trade-offs involved in the usage of OFDMA, especially considering that the standard leaves much of the actual scheduling algorithmic details to vendor-specific implementation. In this work we validate the recent OFDMA implementation in ns-3's wifi module, within the context of a re-design effort to improve modularity and support for future WiFi amendments. ns-3 based OFDMA performance evaluation via simulation is shown to match the predictions of an analytical approach in some simplified scenarios.

In this paper, we develop a novel throughput- maximizing OFDMA scheduler for the multi-user MAC framework for the IEEE 802.11ax networks. The scheduler works both in the downlink and uplink directions and assigns resource units to stations using a linear programming technique considering load of each client, possible resource unit configurations, modulation-coding scheme of each client, and ageing factor of each client's load. The performance of the proposed scheduler has been evaluated using the NS3 simulator and compared against the legacy MAC layer mechanism of IEEE 802.11 protocol (i.e., DCF/EDCA). Simulation results show that our proposed throughput-maximizing scheduler increases the total throughput in the network as well as decrease the average end-to-end delay regardless of the number of stations connected to the access point by prioritizing the traffic of clients connected via high modulation-coding schemes.

The Next Generation Networks (NGN) set its standard to provide very high data rates, Ultra-Reliable Low Latency Communications (URLLC), increased network capacity and significantly improved Quality of Service (QoS). Thus, it provides an infrastructure for the Internet of Things (IoT) to power billions of connected devices. With this upsurge in IoT devices, the need for adopting IPv6 over exhausting IPv4 addresses becomes more unavoidable. Hence, Internet Service Providers (ISP's) are adopting IPv6 along with IPv4 addresses using an address transition method called dual-stack. However, the Dual-Stack network causes relatively more connectivity overhead than the single stack network. For example, DNS lookup and TCP connection time are comparatively high in dual-stack mobile devices. This affects the page loading time of the application, thereby impacting the user experience significantly. In this paper, we analyzed all these connectivity overheads and propose a novel solution called NexGen Connectivity optimizer (NexGenCO), which provides better connectivity for the applications using network-aware concurrency and intelligent DNS caching. NexGenCO is prototyped and evaluated in Samsung devices with Android Pie. It significantly reduces connectivity overhead and improves page loading time up to 18% consistently.

To overcome the lack of spectrum resources, the proposal of extending LTE (Long Term Evolution) to the readily available unlicensed spectrum is receiving much attention. However, gaining capacity in a band where Wi-Fi is widely used and guaranteeing fairness between systems is not an easy to address issue. Analyzing the impact of operating LTE in the unlicensed band on the performance of Wi-Fi and devising solutions to minimize such an impact have been the goals of a considerable amount of work carried out by the research community, standardization bodies and telecom operators. In this paper, we first present a basic overview of Wi-Fi and LTE, which serves the purpose of illustrating why the fair coexistence of the two technologies in the unlicensed band is an issue. Basically, since LTE has been designed to operate in licensed bands, the centralized scheduling performed by LTE eNodeBs saturates all the channel resources, while Wi-Fi stations refrain from transmitting if the channel is sensed busy. Then, we illustrate the main approaches proposed to ensure a fair coexistence between Wi-Fi and LTE in the unlicensed band, namely Listen Before Talk (LBT) and Almost Blank Subframe (ABS), along with some other minor techniques. We describe the main solutions that are currently being developed by standardization bodies and telecom industry: LTE–U, Licensed Assisted Access (LAA) and MuLTEfire. Finally, we present an overview of the work appeared in the literature analyzing the impact of LTE on the performance of Wi-Fi and proposing solutions to mitigate such an impact.

The problem of bufferbloat arises due to the presence of large unmanaged buffers and leads to high queuing delays and significant degradation in the performance of time-sensitive and interactive Internet applications. Recently, a new smart queue management system called Common Applications Kept Enhanced (CAKE) has been introduced in Linux 4.19 to tackle the problem of bufferbloat in home Internet gateways. One of the integral parts of CAKE system is COBALT (CoDel and BLUE Alternate), a queue discipline which is a combination of Controlled Delay (CoDel) and BLUE algorithms. Although CAKE is a part of the Linux kernel, a detailed discussion on the design of COBALT is missing. In this paper, we discuss the design of COBALT and compare its performance with CoDel. Additionally, we propose a simulation model for COBALT in ns-3 and test its correctness by comparing the results obtained from it to those obtained from the Linux model. Our evaluation shows that COBALT offers substantial benefits in terms of curtailing queue delays when unresponsive flows exist.

Long-term evolution (LTE) architecture has recently been enhanced by means of the introduction of multi-antenna systems that make use of multiple input multiple output (MIMO) technology, both at the base transceiver station (eNodeB) and user equipment (UE). MIMO can deploy transmission diversity to achieve more robust transmission in poor propagation conditions and spatial multiplexing to increase throughput and thus LTE performance from an end-user perspective. The most recent version of the standard (Release 10) makes up to eight antennae available for the downlink transmission channel. The paper focuses on the most relevant physical-layer parameters used by LTE to optimise a MIMO system. Performance at different frequencies and bandwidths is investigated over a wide urban area in order to study the network behaviour in actual propagation conditions and to verify whether standard prescriptions are satisfied by a fully operational LTE mobile communication system.

In this work, we propose an innovative approach to contrast the bufferbloat, one of the primary sources of queueing latency, in 3GPP mobile networks. Our purpose is to validate an all-software, in-node traffic-control infrastructure, similar to what the Linux operating system already employs for Ethernet and WiFi networks. We introduce the IP trafficcontrol infrastructure in the RAN part of an LTE network, for both UE and eNB, that can perform packet scheduling on flows directed to the same Data Radio Bearer. The effectiveness of such strategy leverages on a reduced usable size of the in-node RLC buffer, thanks to the BQL algorithm, which we evaluate for the first time in the context of LTE. By using BQL, we can create a backlog of packets that stays in the Traffic Control layer, on which it is possible to perform packet scheduling without bloating the RLC buffer. We compare the performance of BQL to another algorithm, called DynRLC, proposed to dynamically size the RLC buffer eNB side. The preliminary evaluation of the proposed approach is done on the ns-3 network simulator and it shows that the proposed approach with BQL significantly improves the flow delay, by controlling the queueing latency, as well as enhancing the flow isolation., Grant numbers : This work was partially funded by Spanish MINECO grant TEC2017-88373-R (5G-REFINE).