John A. Schormans

Accuracy of packet loss monitoring over networked CPE

In this paper we study the accuracy achievable when using probing to measure packet loss probability. Active monitoring using packet probing is widely used to measure network performance at the packet level, especially where direct measurements from network nodes is not possible. In this paper we develop an analytical solution that allows us to predict the number of samples (probes) needed to measure packet loss probability. This formula relates the number of probes needed to the networking scenario, the traffic characteristics, the target packet loss probability and the accuracy to which this loss probability must be resolved. We show that the number of probes required to accurately measure the packet loss probability is a highly sensitive function of the link bandwidth, the traffic load and burstiness, and the packet loss probability itself. We quantify how many probes are needed in certain typical scenarios involving either VoIP or generic data traffic models.

User-vote assisted self-organizing load balancing for OFDMA cellular systems

Load balancing (LB) is an important function of the self-organizing network (SON) for coping with the uneven load distribution to achieve higher spectrum efficiency and lower operational expenditure. This paper proposes a cluster based self-organizing LB scheme, which employs a user-vote mechanism to avoid the ‘virtual partner’ problem experienced by current LB schemes with the load-based partner selection. The user-vote can assist the hot-spot base station (BS) to efficiently select partner BSs for constructing its cluster, and then shift the traffic to the partners within the cluster. Simulation results show that the proposed scheme can effectively solve the ‘virtual partner’ problem. Furthermore, it can reduce the call blocking rate via a small number of partner BSs.

User Relay Assisted Traffic Shifting in LTE-Advanced Systems

In order to deal with uneven load distribution, mobility load balancing adjusts the handover region to shift edge users from a hot-spot cell to the less-loaded neighbouring cells. However, shifted users receive the reduced signal power from neighbouring cells, which may result in link quality degradation. This paper employs a user relaying model and proposes a user relay assisted traffic shifting (URTS) scheme to address this problem. In URTS scheme, a shifted user selects a suitable non-active user as relay user to forward signal, thus enhancing the link quality of the shifted user. Since the user relaying model consumes relay users energy, a utility function is designed in relay selection to reach a trade-off between the shifted users link quality improvement and the relay users energy consumption. Simulation results show that the URTS scheme can improve SINR and capacity of shifted users. Also, URTS scheme keeps the cost of relay users energy consumption at an acceptable level.

Measurement of packet loss probability by optimal design of packet probing experiments

Packet-level measurement is now critical to many aspects of broadband networking, for example for guaranteeing service level agreements, facilitating measurement-based admission control algorithms and performing network tomography. Because it is often impossible to measure all the data passing across a network, the most widely used method of measurement works by injecting probe packets. The probes provide samples of the packet loss and delay, and from these samples the loss and delay performance of the traffic as a whole can be deduced. However, measuring performance like this is prone to errors. Recent work has shown that some of these errors are minimised by using a gamma renewal process as the optimal pattern for the time instants at which to inject probes. This leaves the best rate at which to inject probes as the key unsolved problem, and this is addressed here by using the statistical principles of the design of experiments. The experimental design approach allows one to treat packet-level measurements as numerical experiments that can be designed optimally. Modelling the overflow of buffers as a 2-state Markov chain, the systems likelihood function is deduced, and from this a technique (using the Fisher information matrix) to determine the upper-bound on the optimal rate of probing is developed. A generalisation of this method accounts for the effect of the probed observations interfering with the experiment. The numerical results focus on VoIP traffic, allowing one to show how this methodology would be used in practice. One application of this is in measurement-based admission control algorithms, where the technique can be used to provide an upper-bound on the rate at which probes should be injected to monitor the loss performance of the target network, prior to making an admit/do not admit decision.

A Hybrid Technique for Accelerated Simulation of ATM Networks and Network Elements

Conventional simulation of cell- or packet-switched networks involves the use of discrete event simulators that model each individual cell through the network, typically called cell-level simulation. Each cells arrival at, or departure from, a network element is represented by an event. However, statistical considerations are such that very large numbers of cells have to be simulated to guarantee the accuracy of the results. This has always caused very long simulation times, often amounting to many hours of real time just to simulate a few minutes of simulated time. In this article we describe a novel methodology for accelerating simulation studies in cell-based communication networks, e.g., ATM, by using a hybrid analytical/simulation combination. The methodology uses a mathematical technique to seperate foreground traffic from background traffic, and focuses on accelerating cell by cell simulation.

Measurement-based end to end latency performance prediction for SLA verification

End-to-end delay is one of the important metrics used to define perceived quality of service. Measurement is a fundamental tool of network management to assess the performance of the network. The conventional approach to measure the performance metrics is on an intrusive basis that may cause extra-burden to the network. In contrast to this, our scheme can be considered as non-intrusive. The main idea relies on the knowledge of the queuing behaviour. The queue length is non-intrusively monitored, and then we capture the parameters of the queue state distribution of every queue along the path in order to deduce the end-to-end delay performance.

Energy-aware adaptive restricted access window for IEEE 802.11ah based smart grid networks

Restricted Access Window (RAW) has been introduced to IEEE 802.11ah MAC layer for application of smart grid networks to decrease collision probability. The number of devices involved and duration affect both transmission energy and overhead information. However, few work has been done on energy efficient RAW. In this paper, we investigate an energy efficient RAW optimization problem for IEEE 802.11ah based uplink communications. We first formulate the problem based on overall energy consumption and the data rate of each RAW by applying probability theory. Then, we derive the energy efficiency of the uplink transmission. Last but not the least, an access window algorithm to adapt the RAW size is proposed to optimise the energy efficiency by identifying the number of contending devices and the number of slots in each RAW. Simulation results show that our proposed algorithm outperforms existing RAW on uplink energy efficiency.

Overflow probability in shared cell switched buffers

The ubiquity of the cell switching technique is a clear indication of its continued importance for the future of telecommunications worldwide. The performance of shared buffers in cell switches provides substantial improvement over switches with separate output buffers. The conventional approach to shared buffer analysis is numerical convolution; however, previous work provides an analytical solution based on the Chernoff bound. In this paper we develop a new closed-form expression for the cell loss probability in the shared buffer that offers superior accuracy, enhanced simplicity, and better generality.

Evaluating the Accuracy of Active Measurement of Delay and Loss in Packet Networks

Performance measurement of packet (e.g. IP) networks is a vital element in the commercial viability of broadband. Active measurement by injection of probing packets will be very widely used as a method of performance measurement. In this paper we quantify the error when using probing. We discover that, when measuring the mean packet delay across a WAN through a representatively loaded (i.e. 50%–90% utilised) access link, the measurements often have an error of many tens, hundreds or even thousands of milliseconds. Furthermore, we apply results from queueing analysis to show that probing for packet loss will require that the probes be about the same size as the data packets; if small packets are used the measured packet loss probability will be many orders of magnitude smaller than it actually is. When this is accounted for, i.e. by using probing packets the same size as the data packets, then, for constant probing load (i.e. a smaller number of larger packets), the error in the returned delay measurements becomes considerably worse.

Energy-aware adaptive restricted access window for IEEE 802.11ah based networks

Restricted Access Window (RAW) has been introduced for IEEE 802.11ah MAC layer to decrease collision probability. However, both the number of devices involved and duration of a RAW affect the transmission energy and overhead information. In this paper, we study the energy efficiency of the uplink communications of IEEE 802.11ah networks and propose an access window algorithm using probability theory to find an optimal number of devices contending in adaptive RAW size. We formulate the problem of RAW optimization based on the overall energy consumption of different transmission states and the data rate in one RAW. The optimal solution is derived by applying a Hill Climbing approach. Simulation results show that our proposed algorithm outperforms existing RAW on uplink energy efficiency.