Mitsuo Hayasaka

A seamless handoff scheme with new AP module for wireless LANs support VoIP

Recently, wireless LANs based on the IEEE 802.11 standard have become popular and widely used, and voice over IP (VoIP) is one of the most promising to be used in mobile devices over wireless networks. Up to date, new technologies have improved providing high data rate to support various kind of real-time applications. However, besides the need for higher data rates, seamless handoff is another important issue to be addressed in order to continue supporting realtime services across wireless LANs. In this paper, we proposed a seamless handoff scheme that uses access point (AP) module with 2 transceivers in order to improve network efficiency in terms of supporting seamless handoff and balancing the traffic load in wireless network. In our proposed scheme, APs use the second transceiver to search for information of neighbor STAs in the transmission range, and later send the result back to associate AP, which in turn compare and analyze whether the STA should perform a handoff or not. The initial results from our simulations show the proposed handoff scheme is more effective than the conventional scheme in terms of low latency and traffic load is fairly balanced.

Packet/cell loss recovery using variable FEC matrix for real time transport services over best effort networks

Real-time services over best-effort networks, such as teleconferencing over unspecified bit rate (UBR) class asynchronous transfer mode (ATM) networks or the Internet, are expected to be in high demand in the near future as such services become more cost effective. However, cell loss caused by buffer overflow at switches is a serious problem in this service class, and is responsible for degradation of the quality of service (QoS). A promising technology for improving the QoS of best-effort networks is the recovery of lost cells by forward error correction (FEC). Conventional FEC methods utilize a FEC matrix with fixed dimensions and which is usually designed to cope with the worst case of cell loss. In this paper, a new method that provides dynamic recovery capacity to deal with the current cell loss ratio through the use of a variable-dimension FEC matrix is proposed. The scheme also takes into account the coding method of the matrix to provide data prioritization. Numerical results show that the cell loss ratio and transmission efficiency of the proposed method are superior to those of conventional methods.

Implementation of virtual path hopping (VPH) as a solution for control plane failures in connection oriented networks and an analysis of traffic distribution of VPH

A connection oriented next generation Internet could guarantee the QoS preferred by the emerging real time applications. These connection oriented networks are inherently more prone to network failures: link/path failures and degraded failures. The control and the data plane of connection oriented networks such as MPLS are logically separated. Therefore a failure in the control plane should not always immediately affect the communications in the data plane. Control plane failures are usually detected using Timers. If any of the Timers expire, the control plane session is terminated resulting failures in the corresponding data plane. This paper discusses in detail the implementation of VPH concept that intent to eliminate the degraded type failures in the data plane and its advantages. Also this evaluates a more efficient, non-periodic VPH concept. The results of the computer simulations show VPH is a proactive technique to eliminate degraded type failures and improve the availability of the networks.

Virtual path hopping to overcome network failures due to control plane failures in connection oriented networks

Real time traffic is a predominant traffic type in the next generation communication IP networks and the future applications demand for 100% reliability and availability of networks. The guarantees of QoS expected can be achieved by connection oriented networks such as MPLS. The control plane and the data plane of MPLS are logically separated Therefore any failures in the control plane not necessarily should affect the communication sessions in the data plane. Label distribution protocol (LDP) which is preferred over RSVP as a control plane protocol in MPLS, uses TCP in the transport layer for most of its message transmissions. TCP resets all the participating peers, at any terminations of LDP sessions, leading the applications to terminate the corresponding data plane communications. If the keep alive timers of the LDP peers expire without receiving protocol data units (PDU) from the neighboring peers, it terminates the LDP session resulting in a network failure due to control plane failure. None of the existing restoration schemes distinguish this type of control plane failures from the normal data plane path/link failures. It is found that about 50% of the network failures are of this type and if they can be avoided without disturbing the data plane, it will improve the availability and the reliability of the connection oriented networks drastically. A novel idea of virtual path hopping (VPH) is proposed, which can avoid all the control plane failures from affecting the communications in the data plane. The computer simulations performed, prove that it is possible to avoid about 50% re-routings due to failures in the data plane and this explains that the control plane failures are looked after by the VPH concept.

A novel handover scheme for reducing latency in WLANs

Recently, wireless LANs have become widely used. New technologies have improved providing high data rate and support for real-time services such as Voice over IP (VoIP). However, besides the need for higher data rates, handover latency time is another important issue to be addressed in order to avoid the bottleneck problem and support real-time services. In this scheme, we improve network efficiency in terms of reducing the latency time in the handover process. We neglect both Detection phase and Search phase by proposing a Pre-Active Scan phase, which works during normal connectivity. This phase will scan for information of neighbor Access Points (AP) by using an active scan mode, which in turn is used to decide whether to perform a handover or not. The initial results from our simulations show that the proposed handover scheme is more effective than the conventional scheme in terms of latency and reveals a rather small effect on network traffic load. requirements of real-time applications such as Voice over IP. The detection phase is the longest phase in all cases, while the execution phase could be neglected. So, we consider that a new handover scheme is necessary to improve the latency time in WLAN. This can be achieved by reducing the delay of handover process as much as possible in order to support real-time services and avoid packet losses. In this paper, we propose a new phase called pre-active scan phase to replace both detection phase and search phase in the conventional handover scheme. The pre-active scan phase scan neighbor APs and compare the results with the current AP, then STA will make a decision when and which AP the STA will handover in order to reduce latency time in WLANs.

Weighted Hop Priority Control Scheme for Multihop Wireless Ad Hoc Networks

Packet scheduling problem experienced in wireless ad hoc networks is presented. Flow of packets coming from different node locations and concurring at intermediate nodes could overflow resources rapidly, stressing packet forwarding and increasing packet dropping. An intelligent packet priority control technique named weighted hop priority control scheme is used, that assures a data arrival end-to-end and reduced packet dropping ratio. Technique is based on periodically calculating two hop threshold values by weighting hop information carried by incoming and outgoing packet flows (hops already traversed and still remaining) respectively with their correspondent data rates, and using these thresholds to prioritize packet forwarding. Proposed scheme is compared with conventional queuing control based on first-in first-out queue dispatcher. Data arrival ratio and downloading response time are evaluated as our main estimator parameters. An ad hoc network scenario is simulated and results show that our proposed priority control scheme is a promising technique to efficiently handle packet flow forwarding in wireless ad hoc communications

A Novel Handover Scheme for Improving the Performance of WLANs based on IEEE802.11

Recently, new technologies improve WLANs to provide high quality of service (QoS) and support real time applications. In this paper, we improve network efficiency in terms of reducing the latency time in handover process and support traffic load sharing among neighbor access points (APs). We neglect both detection phase and search phase in the conventional handover scheme by proposing a pre-active scan phase, which works during normal connectivity. This phase will scan for the information of neighbor APs, which in turn is used to decide whether to perform a handover or not. The results from our simulation show the proposed handover scheme is more effective than the conventional one in terms of providing low latency time and support traffic load sharing among neighbor APs

The Concept of Referential Loss Recovery for Real-Time Applications and its Improvements of QoS Provision

Real-time multimedia streaming is expected to grow rapidly in the near future. Packet losses during transmission are a serious problem for these multimedia applications since they result in degradation of the quality of service (QoS). Forward error correction (FEC) is a promising technique to recover the lost packets and improve the QoS of streaming media. However, FEC may degrade the QoS of all streaming due to the increased congestion caused by FEC overhead when streaming sessions increase. In this paper, a novel FEC method that avoids the adverse effect of FEC overhead during media streaming is proposed. Also, we define the maximum percentage of network load where FEC can improve the packet loss ratio to clarify the effective ranges where each FEC and automatic repeat request (ARQ) scheme works well. The numerical analyses show that our proposed method highly improves the packet loss ratio compared to conventional method

A Network Architecture with High Availability for Real-time Premium Traffic over the Internet

Real-time traffic will be a predominant traffic type in the next generation networks, and networks with 100% reliability and availability will be required by real-time premium traffic. It is believed that QoS guarantees could be better provided by connection oriented networks such as Multi Protocol Label Switching (MPLS). These connection oriented networks are more vulnerable to network failure. Conventional path protection methods perform re-routing to cope with this. However, re-routing always causes packet losses and results in service outage. These losses are bursty in nature and highly degrade the QoS of the real-time premium traffic. Thus, 100% availability cannot be achieved by conventional methods. The novel path protection proposed in this paper recovers the bursty packet losses due to re-routing by using forward error correction (FEC) path. Therefore, it can provide network architecture with no service outage for such traffic. The numerical results show that the proposed method can achieve a very high availability for real-time premium traffic in future IP/MPLS networks.

Seamless Failure Recovery for Real-time Premium Traffic in MPLS Networks

Real-time traffic will be a predominant traffic type in the next generation networks and 100% reliability and availability of networks will be required by real-time premium traffic (PT). It is believed that QoS guarantees could be better provided by the connection oriented networks such as Multi Protocol Label Switching (MPLS). These connection oriented networks are more vulnerable to network failures. Conventional path protections perform re-routing to cope with them. However, re-routing always causes packet losses and results in service outage. These losses are bursty in nature and highly degrade QoS of the real-time premium traffic. The novel path protection proposed in this paper recovers the bursty packet losses due to re-routing using forward error correction (FEC) path. Therefore, it can provide the network architecture with no service outage for such traffic. The numerical results show that the proposed method can achieve a very high availability for the real-time premium traffic in future IP/MPLS networks. routing (4). However, the problem of re-routing mentioned above still exists, and therefore it is necessary to find proactive techniques to recover the bursty packet losses due to re- routings. The novel idea of path protection with forward error correction (FEC) path proposed in this article can be used for real time premium traffic that needs a guaranteed QoS. It combines a FEC path with conventional path protection methods using re-routings and recovers the packet losses due to re-routings by way of a FEC recovery technique. The numerical result shows that this is a promising proactive technique to provide a guaranteed QoS for real time premium traffic that otherwise can lead to severe effects if 100% availability is not achieved. The rest of this paper is organized as follows. In the next section, the problem description and the existing solutions are analyzed briefly. In Section III, we discuss the proposed method in detail. The performance of the proposed method is evaluated and the results are presented in Section IV. Finally this paper is concluded in Section V.