Enhanced power saving through increasing unavailability interval in the IEEE 802.16e systems

The power saving mechanisms of the current IEEE 802.16e system are designed to take no consideration of the harmonization between power saving classes (PSCs) I and II. Using the IEEE 802.16e standard as a basis, we propose a dynamic power saving mechanism that increases unavailability interval when a mobile station (MS) uses PSCs. The proposed mechanism adjusts the timing of the sleep window of PSC I to maximize the unavailability interval of the MSs. As a result, the proposed scheme achieves power saving of the MSs. Through numerical analysis and simulations, we show that the proposed mechanism can reduce the power consumption of the MSs considerably compared with conventional mechanisms.     

PIANO: A power saving strategy for cellular/VoWLAN dual-mode mobiles

The integration of cellular and VoIP over WLAN (VoWLAN) systems recently has attracted considerable interest from both academia and industry. A cellular/VoWLAN dual-mode system enables users to access a low-cost VoIP service in a WLAN hotspot and switch to a wide-area cellular system without WLANs. Unfortunately, cellular/VoWLAN dual-mode mobiles suffer the power consumption problem that becomes one of the major concerns for commercial deployment of the dual-mode service. In this study, we present a novel power saving mechanism, called PIANO (paging via another radio), for the integration of heterogeneous wireless networks, and further apply the proposed methods to implement a cellular/VoWLAN dual-mode system. Based on the proposed mechanisms, a dual-mode mobile can completely switch off its WLAN interface, only leaving the cellular interface awake to listen to paging messages. When a mobile receives a paging message from its cellular interface, it wakes up the WLAN interface and responds to connection requests via WLAN networks. Therefore, a dual-mode mobile reduces the power consumption by turning off the WLAN interface during idle, and can also receive VoWLAN services. Measurement results based on the prototype system demonstrate that the proposed methods significantly extend the standby hours of a dual-mode mobile.     

Contention‐free approaches for WiFi MAC design for VoIP services: performance analysis and comparison

The exponential growth in the demand of voice over internet protocol (VoIP) services along with the increasing demand for mobility in VoIP services has attracted great research efforts towards provisioning of VoIP services in IEEE 802.11‐based Wireless LANs (WiFi networks). We address one of the important research problems, namely, the quality of service (QoS)‐aware efficient silence suppression in the bursty voice traffic, for provisioning VoIP services in WiFi networks. The research works in the recent literature on silence suppression in voice calls have been surveyed categorising them on how the activity arrival is notified to the access point (AP). In most of the recent schemes, notification of uplink activity arrival is done through contention based medium access mechanisms such as the distributed coordination function (DCF). Contention‐based medium access causes non‐deterministic delays, therefore such schemes are not suited to voice traffic which require strict delay bound guarantees. This paper focuses on the schemes which do not use contention based approaches for silence suppression in voice traffic. Analytical performance evaluation and comparison of such schemes is carried out. Two very important performance metrics are modelled mathematically. One is the expected polling overhead time that the schedulers in these schemes can save per voice call during one voice activity cycle as compared to that in the round‐robin polling scheduler. The other is the expected unnecessary wireless channel access delay that a typical first talk‐spurt frame experiences due to the specific design of each scheme. The numerical results of this evaluation lead us to the conclusion whether or not and to what extent each of these schemes is viable. Copyright © 2008 John Wiley & Sons, Ltd.     

Delay versus energy consumption of the IEEE 802.16e sleep-mode mechanism

We propose a discrete-time queueing model for the evaluation of the IEEE 802.16e sleep-mode mechanism of Power Saving Class (PSC) I in wireless access networks. Contrary to previous studies, we model the downlink traffic by means of a Discrete Batch Markov Arrival Process (D-BMAP) with Ν phases, which allows to take traffic correlation into account. The tradeoff between energy saving and increased packet delay is discussed. In many situations, the sleep-mode performance improves for heavily correlated traffic. Also, when compared to other strategies, the exponential sleep-period update strategy of PSC I may not always be the best.     

Efficient silence suppression and call admission control through contention-free medium access for VoIP in WiFi networks

In view of the rapidly growing trend of migrating customers from traditional wired phones to mobile phones and then to VoIP services in the recent past, there is a tremendous demand for wireless technologies to support VoIP, specially on WiFi technologies which have already matured commercially. This has put forth great research challenges in the area of wireless VoIP. In this article we have addressed two core issues, efficient silence suppression and call admission control, in QoS provisioning for VoIP services in WiFi networks. In this connection we present a QoS-aware wireless MAC protocol called hybrid contention-free access (H-CFA) and a VoIP call admission control technique called the traffic stream admission control (TS-AC) algorithm. The H-CFA protocol is based on a novel idea that combines two contention-free wireless medium access approaches, round-robin polling and TDMA-like time slot assignment, and provides substantial multiplexing capacity gain through silence suppression of voice calls. The TS-AC algorithm ensures efficient admission control for consistent delay bound guarantees and further maximizes the capacity through exploiting the voice characteristic so that it can tolerate some level of non-consecutive packet loss. We expose the benefits of our schemes through numerical results obtained from simulations.     

加拿大VoIP的管制现状及对我国的启示

加拿大监管部门对VoIP监管的主要内容是从业务而不是从技术层面上考虑,将其纳入电路交换语音业务的管制范围内,如同样使用北美编号计划（NANP）的号码,对传统运营商和竞争性运营商实施非对称资费管制等。我国应实行许可证准入制度,建立对拥有网络资源的传统运营商的补偿机制,制定出激励相容的VoIP监管政策,杜绝服务商良莠不齐现象,保证VoIP的良性发展。     

VoIP市场监管现状及市场进入途径初探

在国内，目前VoIP业务的市场监管尚不明朗．但由于市场需求旺盛．已经有大量服务提供商进入市场，分析VoIP在中国的监管现状。并通过详细的调查，列举了在目前监管框架下VoIP服务提供商进入市场的几种模式，给从业者以启发。同时，也对于VoIP管制的着眼点提出了新的思考。     

Typed VoIP Silence Prediction for Smartphone Energy Savings

Previous research has shown that considerable energy savings may be made in Android phones by intelligently switching the WiFi radio from Constantly Awake Mode (CAM), to Power Save Mode (PSM) during periods of mutual silence in Voice over IP calls. This is because a WiFi radio in CAM consumes approximately one third of a smartphones battery life. Since a typical conversation can consist of up to 60 % silence, much of a conversation need not be transmitted, and thus wastes a considerable amount of battery power. This research shows that as much as 40 % of that energy can be saved by switching the radio to PSM during mutual silence periods. However, this technique relies heavily on accurately predicting the duration of such silence periods. This paper presents and compares a silence model which uses speaker identity to build a typology of silences to a naive un-typed strategy. This type model relies on recent research showing statistical difference between the durations of classes of silences based on speaker identity before and after a silence. Evaluation of this technique, however, demonstrates that such models do not show improvement over more naive strategies. Thus, a naive strategy is perfectly sufficient for accurate prediction of silence duration.     

Load-Based Power Saving in IEEE 802.16j Multi-Hop Relay Networks

In this paper, our previous work of Load-Based Power Saving (LBPS) for energy saving at the user side is extended to support integrated sleep scheduling for BS, RS, and MSS in the IEEE 802.16j Multi-Hop Relay Network. Topology-dependent time frame structure is adopted in our design to reduce the transmission delay in the relay network, in which the number of relay zone (for transmission over the relay link) depends on the hop count of RS in the network. Focused on non-real-time traffic, two LBPS schemes, namely LBPS-Aggr-MR and LBPS-Merge-MR, are proposed. Simulation study shows the proposed LBPS schemes significantly outperform the standard Type I PSC in terms of power saving efficiency.     

vGPRS: A Mechanism for Voice over GPRS

This paper proposes vGPRS, a voice over IP (VoIP) mechanism for general packet radio service (GPRS) network. In this approach, a new network element called VoIP mobile switching center (VMSC) is introduced to replace standard GSM MSC. Both standard GSM and GPRS mobile stations can be used to receive real-time VoIP service, which need not be equipped with the VoIP (i.e., H.323) terminal capabilities. The vGPRS approach is implemented using standard H.323, GPRS, and GSM protocols. Thus, existing GPRS and H.323 network elements are not modified. Furthermore, the message flows for vGPRS registration, call origination, call release and call termination procedures are described to show the feasibility of our vGPRS system.     

Implementing VoIP: a voice transmission performance progress report

Aiming to introduce voice over IP networks and services in ways that satisfy the voice quality expectations of our customers, we have been conducting laboratory studies of how VoIP transmission affects voice quality while also carefully monitoring and managing several field implementations of VoIP. This article summarizes much of what we have learned in this work, and we hope it provides a useful progress report on the industry's evolution to VoIP. We review our data on the voice quality effects of packet loss, delay, speech coders, packet loss concealment algorithms, and the compression option of suppressing transmission during silence. Because the familiar problem of echo has emerged repeatedly in the VoIP environment, we review this issue in some detail. Packet loss and delay variation measurements made on private VoIP networks are reviewed, and the data here are encouraging. We finish by making our case that the network planning tool known as the E-model is currently an inexact predictor of VoIP network performance.     

An energy‐efficient transmission mechanism for VoIP over IEEE 802.11 WLAN

Voice over IP (VoIP) over WLAN (VoWLAN) is an important application for public and private WLANs. However, VoWLAN systems suffer from several technical challenges such as power consumption of a WLAN station (STA) and service capacity of an access point (AP), making the commercial deployment of a large‐scale VoWLAN service problematic. This study presents a cross‐layer and energy‐efficient mechanism for transmitting VoIP packets over IEEE 802.11 WLAN. The proposed mechanism considers the characteristics of voice packets that can tolerate certain loss, and dynamically disables the medium access control (MAC) layer acknowledgement for voice packets. In doing so, the time and energy consumed to transmit and receive voice packets for an STA can be reduced. Simulation results demonstrate that the mechanism improves the energy efficiency of a VoWLAN STA and WLAN utilization without sacrificing voice qualities. Copyright © 2009 John Wiley & Sons, Ltd.     

Seven myths about voice over IP

Voice over Internet Protocol (VoIP) is one of the fastest growing and most misunderstood technologies in the world at the moment. Confusion, outdated beliefs and urban mythology reign over such simple issues as how it works, the quality of the calls, and, of course, how much it costs. This paper examines seven existing myths about VoIP. These myths are that: (1) VoIP is free; (2) the only difference between VoIP and regular telephony is the price; (3) the quality of service isn't an issue nowadays because there's plenty of bandwidth in the network; (4) VoIP can't replace regular telephony because it still cannot guarantee quality of service; (5) VoIP is just another data application; (6) VoIP isn't secure; and (7) a phone is a phone is a phone.     

Effective VoIP call routing in WLAN and cellular integration

In cellular-WLAN integration, a dual-mode mobile station (MS) typically disables the WLAN module for power saving. A major problem is that for an incoming VoIP call (or data session), the MS will not be able to receive this call from the WLAN. It turns out that the call is directed to the cellular network. This letter proposes a simple push solution where an MS can accurately detect a VoIP call from paging signaling of the cellular network. Then the WLAN module of the MS is turned on and the VoIP call is connected to the MS through the relatively inexpensive WLAN.     

VoIP: A debate over information service or telephone application in US: A new perspective in convergence era

As new voice-over-IP (VoIP) services rapidly emerge, a debate is growing over how the emerging technology fits into the traditional telecommunications regulation and industrial schemes. The debate on VoIP has been whether VoIP traffic should be subjected to any or all of the various common carrier regulations. VoIP sparked a regulatory debate whether it is phone call service, which will have a great impact on telecom industry’s business or just information service. Because of the complexity of the issue, and the intent to let the premature technology grow, the FCC has so far taken a hands-off approach taking tentative assumption that VoIP is not a telecom service. Under the provisional hand-off approach, VoIP providers are exempt from rules that govern telecom services. However, traditional service providers argue that VoIP should be classified as a telecom service and take equal responsibilities as traditional voice calls. VoIP providers counter argue that incumbent telcos can easily dominate market driving VoIP providers out of the market. They request new legislation that protects the services from being hit with access charges from entrenched telco. This paper reviews the nature of these debates, outlines the challenges faced by regulators, briefly summarizes how other countries’ views may have to adapt and offer new praxis that will benefit the consumers in the long run.     

Performance analysis of power saving class of Type III in IEEE 802.16e with user initiated traffic

A novel method for analysing the performance of power saving class of Type III in IEEE 802.16e is proposed, which is applicable to design, maintenance and management for mobile wireless metropolitan area network. Considering the memoryless nature of user initiated packet arrival, a Geom/G/1 queue model with multiple vacations and setup period is built to capture the principle for the power saving class of Type III. By using an embedded Markov chain method and the boundary state variable theory, we obtain the queueing measures such as queueing length, waiting time and busy cycle in steady state. Correspondingly, we derive explicitly the performance measures for the power saving class of Type III in terms of handover ratio, energy saving ratio, and average packet response time. Based on numerical results, we develop a cost function to determine numerically the optimal length of sleep window and the minimal cost with different offered loads.     

Performance evaluation of packet aggregation scheme for VoIP service in wireless multi-hop network

In a wireless multi-hop network environment, energy consumption of mobile nodes is an important factor for the performance evaluation of network life-time. In Voice over IP (VoIP) service, the redundant data size of a VoIP packet such as TCP/IP headers is much larger than the voice data size of a VoIP packet. Such an inefficient structure of VoIP packet causes heavy energy waste in mobile nodes. In order to alleviate the effect of VoIP packet transmission on energy consumption, a packet aggregation algorithm that transmits one large VoIP packet by combining multiple small VoIP packets has been studied. However, when excessively many VoIP packets are combined, it may cause deterioration of the QoS of VoIP service, especially for end-to-end delay. In this paper, we analyze the effect of the packet aggregation algorithm on both VoIP service quality and the energy consumption of mobile nodes in a wireless multi-hop environment. We build the cost function that describes the degree of trade-off between the QoS of VoIP services and the energy consumption of a mobile node. By using this cost function, we get the optimum number of VoIP packets to be combined in the packet aggregation scheme under various wireless channel conditions. We expect this study to contribute to providing guidance on balancing the QoS of VoIP service and energy consumption of a mobile node when the packet aggregation algorithm is applied to VoIP service in a wireless multi-hop networks.     

日本VoIP的管制现状及对我国的启示

日本是世界上VoIP发展较快的国家之一,以传统电话网络IP化为目标,在一开始就将VoIP纳入了已有的管制范围内。管制枢架的修改中最重要的最消了按有无电信设施划分第一类、第二类电信运营商的规定,并在市场准入、退出制度方面取消了许可制,改为登记、报备制,引进了公益事业特权许可制度,并对两种等级的VoIP业务设置了不同的准入规定。但目前VoIP尚未纳入普遍服务的范畴。     

A push mechanism for GPRS supporting private IP addresses

The General Packet Radio Service (GPRS) provides a packet switched data service for mobile users. However, the existing GPRS specification does not provide the push mechanism and it is difficult to support GPRS services such as call termination (incoming call) for wireless voice over IP (VoIP). Based on the short message service, this paper proposes a push mechanism for GPRS supporting private IP addresses. Our approach does not need to modify the existing GPRS structure.     

VoIP Performance over HSPA with Different VoIP Clients

High Speed Packet Access (HSPA) Holma H, Toskala A (in HSDPA/HSUPA for UMTS, 2006) is expected to provide enough bandwidth for voice over IP (VoIP) service. In this article we assess the performance of VoIP over HSPA with different VoIP clients and voice codecs. The simulations results show that VoIP can have a good voice quality over HSPA if a proper VoIP client and codec is used. However it is possible that the delay can increase with early HSPA implementations (mobile, network).