A Survey on Enhancing the QoS through voice Quality for Voice over Wireless LANs (VoWLAN)

Voice over Internet Protocol (VoIP) is one of the important technologies that allow voice transmission over the IP network. Various voice codec are available for VoIP as this is a rapidly changing technology. It can be an effective renewal for the traditional telephone systems (PSTN) because of extreme utilization of its sources as well as to provide very low cost. Apart from, Wireless Local Area Network (WLAN) has become apparent as a durable networking technology. Hence, the combination of these two popular technologies is growing so fast all over the world. Voice over WLAN will be a tool to provide low-cost and reliable voice services on wireless media. However just like other wireless applications, VoWLAN has also faced few challenges that need to be considered. Quality of Service (QoS) is one of the primary requirements in different kind of wireless applications. In this survey some of the important QoS requirement (latency, delay, jitter etc) have been analyzed, and it also has the introspection of the E- model and MOS (Mean Opinion Score) value for voice quality while using of different ITU-T codec. Therefore it makes Voice over WLAN a challenging research topic. In this study we will address all VoWLAN issues. DOI: 10.17762/ijritcc2321-8169.150516

Comparison of IPv4 and IPv6 QoS implementations using Differentiated Services

Real-time applications such as VoIP place stringent demands on network QoS. However, IP is a best-effort service and is often unable to offer the levels of QoS required for real-time applications. One mechanism that has been commonly used to address this issue in IP networks is Differentiated Services (DiffServ). This paper describes the use of DiffServ in IPv4 and IPv6 networks, and implementation and evaluation of VoIP QoS within OPNET IT Guru. The simulation results demonstrated that DiffServ improved the performance of VoIP traffic in both IPv4 and IPv6, allowing previously congested networks to deliver VoIP with an acceptable QoS. However the simulations also showed that the performance of DiffServ in IPv6 is slightly worse than in IPv4. A number of possible reasons for this outcome are proposed along with recommendations for further research

The Voice Capacity of WiFi for Best Effort and Prioritized Traffic

Crucial to supporting voice over 802.11b is the knowledge of voice capacity (Nc) of a single Access Point. This paper provides an analytical formulation of Nc in the case where all traffic in the network is voice. Our formulation, which can apply to a range of voice codec specifications, are verified by detailed simulations. We also investigate how to deliver, within the 802.11b standard, priority service to voice in the presence of best effort background traffic. It is known that the voice capacity degrades very quickly in the presence of other traffic sources if all packets are treated as best effort. Using an experimental deployment in which all voice packets are prioritized by having their channel back-off times set to zero, we determine the rate of the best effort background traffic below which our analytical formulation of voice-only capacity remains useful

The VPQ scheduler in access point for VoIP over WLAN

The Voice over Internet Protocol (VoIP) application has observed the fastest growth in the world of telecommunication.VoIP is seen as a short-term and long-trem transmission for voice and audio traffic. Meanwhile, VoIP is moving on Wireless Local Area Networks (WLANs) based on IEEE 802.11 standards.Currently, there are many packet scheduling algorithms for real-time transmission over network.Unfortunately, the current scheduling will not be able to handle the VoIP packets with the proper manner and they have some drawbacks over real-time applications.The objective of this research is to propose a new Voice Priority Queue (VPQ) packet scheduling and algorithm to ensure more throughput, fairness and efficient packet scheduling for VoIP performance of queues and traffics.A new scheduler flexible which is capable of satisfying the VoIP traffic flows.Experimental topologies on NS-2 network simulator were analyzed for voice traffic. Preliminary results show that this can achieve maximum and more accurate VoIP quality throughput and fairness index in access point for VoIP over WLANs.We verified and validated VPQ an extensive experimental simulation study under various traffic flows over WLANs

ボイスIPネットワークのモデリングと高性能化

Tohoku University堀口 進課

Reputation-Based Trust for a Cooperative, Agent-Based Backup Protection Scheme for Power Networks

This thesis research explores integrating a reputation-based trust mechanism with an agent-based backup protection system to improve the performance of traditional backup relay methods that are currently in use in power transmission systems. Integrating agent technology into relay protection schemes has been previously proposed to clear faults more rapidly and to add precision by enabling the use of adaptive protection methods. A distributed, cooperative trust system such as that used in peer-to-peer file sharing networks has the potential to add an additional layer of defense in a protection system designed to operate with greater autonomy. This trust component enables agents in the system to make assessments using additional, behavioral-based analysis of cooperating protection agents. Simulation results illustrate the improved decision-making capability achieved by incorporating this cooperative trust method when experiencing abnormal or malicious communications. The integration of this additional trust component provides an added push for implementing the proposed agent-based protection schemes to help mitigate the impact from wide-area disturbances and the cascading blackouts that often follow. As the push for electric grid modernization continues, an agent-based trust system including this type of behavioral-based analysis will also benefit other smart components connecting critical grid control and monitoring information systems

Call admission control for adaptive bit-rate VoIP over 802.11 WLAN.

Cui, Yuanyuan.Thesis (M.Phil.)--Chinese University of Hong Kong, 2009.Includes bibliographical references (p. 64-68).Abstract also in Chinese.Chapter Chapter 1 --- Introduction --- p.1Chapter 1 .1 --- Motivations and Contributions --- p.1Chapter 1.2 --- Related Works --- p.3Chapter 1.3 --- Organization of the Thesis --- p.4Chapter Chapter 2 --- Background --- p.5Chapter 2.1 --- IEEE 802.11 --- p.5Chapter 2.1.1 --- IEEE 802.11 Topologies --- p.5Chapter 2.1.2 --- IEEE 802.11 MAC --- p.8Chapter 2.2 --- Voice over Internet Protocol (VoIP) --- p.11Chapter 2.2.1 --- A VoIP system --- p.11Chapter 2.2.2 --- QoS requirements for VoIP --- p.11Chapter 2.2.3 --- VoIP speech codecs --- p.12Chapter 2.3 --- VoIP over WLAN --- p.13Chapter 2.3.1 --- System Architecture of VoIP over WLAN --- p.14Chapter 2.3.2 --- VoIP Capacity over WLAN --- p.15Chapter 2.4 --- Skype --- p.16Chapter Chapter 3 --- Skype Rate Adaptation Mechanism --- p.17Chapter 3.1 --- Experimental Setting --- p.17Chapter 3.2 --- Overview --- p.19Chapter 3.3 --- Flow Rate Region --- p.20Chapter 3.4 --- Feedback: Receiver Report (RR) --- p.21Chapter 3.5 --- Bandwidth Usage Target (BM) --- p.24Chapter 3.6 --- Summary of Skype Rate Adaptation Mechanism --- p.28Chapter 3.7 --- Skype-emulating Traffic Generator --- p.28Chapter Chapter 4 --- "Call Admission, Fairness and Stability Control" --- p.32Chapter 4.1 --- Unfair and Instability problems for AVoIP --- p.32Chapter 4.1.1 --- Analysis --- p.32Chapter 4.1.2 --- Simulation Evaluation --- p.34Chapter 4.2 --- CFSC scheme --- p.37Chapter 4.2.1 --- Pre-admission Bandwidth-reallocation Call Admission Control (PBCAC) --- p.39Chapter 4.2.2 --- Fairness Control --- p.42Chapter 4.2.3 --- Stability Control --- p.43Chapter Chapter 5 --- Performance Evaluation of CFSC --- p.44Chapter 5.1 --- Evaluation of Fairness Control --- p.44Chapter 5.2 --- Evaluation of Stability Control --- p.46Chapter 5.3 --- Evaluation of PBCAC --- p.46Chapter 5.4 --- Evaluation of complete CFSC --- p.49Chapter Chapter 6 --- Conclusion --- p.51Appendices --- p.53References --- p.6

Performance of Wi-Fi coordination schemes for VolP in the presence of FTP data.

Evolved 3GPP cellular core networks have made co-existence of heterogeneous Wireless Access networks (HetNets) possible. The evolved core network along with the development of multimode end user devices have led to the realisation of converged Access Networks. Wireless Local Area Networks (WLANs) are assuming a prominent role in the telecommunications ecosystem due to their cost effectiveness, ease of deployment and operation in the free spectrum. Although WLANs are only data centric, there will be greater demand for Voice over Internet Protocol (VoIP) over WLANs as multimode smart-phones become accessible and operators integrate WLANs into their business models. Therefore, it is imperative that WLAN’s ability to support VoIP services is thoroughly understood. Currently, the design of call admission control mechanisms for WLANs that support heterogeneous (data and voice) traffic is a challenging issue. The challenge stems from the difficulty of modelling the behaviour heterogeneous traffic, mixed VoIP and data traffic. IEEE 802.11 WLANs use two types of medium access schemes, the polling based schemes and the contention based schemes. Both types of WLAN coordination schemes have not been thoroughly investigated for their ability to support VoIP over WLANs in the presence of File Transfer Protocol (FTP) data sessions. File Transfer Protocol (FTP) is a Transport Control Protocol(TCP) based file exchange protocol. TCP was optimised for wired networks and as a result it is unsuitable for wireless network. Furthermore, it was not optimised to co-exist with VoIP and as a result of its burstiness it has severe impact on the jitter, packet-loss and delay of VoIP traffic. The purpose of the work presented in this report is to evaluate the performance of Distributed Coordinated Function (DCF), Point Coordination Function (PCF) and Enhanced Distributed Coordinated Function (EDCF) techniques’ ability to manage Voice Over Internet Protocol (VoIP) over WLAN in the presence of contending heavy FTP data. The key question this work seeks to answer is, are the Medium Access Control (MAC) coordination techniques in their present form capable of carrying VoIP data in the presence of other data. In other words, how realistic is the deployment of VoIP services with FTP services in the same network, using the current coordination schemes for WLAN? Can these coordination schemes be improved by using current MAC enhancements such as fragmentation and increasing the Access Point buffer? The study is carried out for IEEE 802.11g as this is still the most widely deployed standard. The performance is evaluated by setting up a network of stations that generate both voice and FTP traffic in OPNET. The two network configurations are 30-Voice stations and 30-FTP stations; 15-Voice stations and 45-FTP stations. Moreover, two codecs G.711 and G.723 are compared to assess the effect of codec selection on performance