Seamless mobility: are we there yet? - [Industry perspectives]

Seamless mobility is the ability for users to remain connected while roaming across different networks. This paper analyses the issues involved in general mobility scenario for seamless mobility and presents the challenges, solutions and opportunities in achieving seamless mobility.     

Protection switching for optical bursts using segmentation and deflection routing

Burst segmentation in OBS networks can significantly reduce the amount of data that is lost due to contention events by dropping or deflecting only the portion of a burst that overlaps another contending burst. In this letter, we demonstrate how segmentation combined with deflection routing can be used to reduce the amount of data that is lost when network elements fail. By enabling an OBS switch to deflect the tail-end segments of bursts that are in transmission as soon as it becomes aware of a downstream link failure, the retransmission of lost data can be reduced.     

Timely Effective Handover Mechanism in Heterogeneous Wireless Networks

Next-generation wireless networks should be able to coordinate and integrate different communication systems. It has been a challenging problem to support a seamless handover in these diverse wireless network environments. Link level triggers can provide information about events which can help handover decision and layer 3 entities better streamline their handover related activities. In most conventional layer 2 triggering approaches, a pre-defined threshold for a specific perspective such as the received signal strength is used. This may cause too late or too early handover executions. In this paper we propose a new predictive handover framework that uses the neighbor network information to generate timely the link triggers so that the required handover procedures can appropriately finish before the current link goes down. First we estimate a required handover time for the given neighbor network conditions, then using a predictive link triggering mechanism the handover start time is dynamically determined to minimize handover costs. The handover costs are analyzed in terms of the total required handover time and the service disruption time. The numerical analysis and simulation results show that the proposed method significantly enhances the handover performance in heterogeneous wireless networks.     

Resource planning and bandwidth allocation in hybrid fiber–coax residential networks

The introduction of new high bandwidth services such as video-on-demand by cable operators will put a strain on existing resources. It is important for cable operators to know how many resources to commit to the network to satisfy customer demands. In this paper, we develop models of voice and video traffic to determine the effect of demand growth on hybrid fiber–coax networks. We obtain a set of guidelines that network operators can use to build out their networks in response to increased demand. We begin with one type of traffic and generalize to an arbitrary number of high-bandwidth constant bit rate (CBR) like services to obtain service blocking probabilities. We consider the effect of supporting variable bit rate (VBR) packet-switched traffic in addition to CBR services. These computations help us to determine how cable networks would function under various conditions (i.e., low, medium, and heavy loads). We also consider how the growth rate of the popularity of such services would change over time, and how this impacts network planning. Our findings will help cable operators estimate how much bandwidth they need to provision for a given traffic growth model and connection blocking requirement.     

Bluetooth Dynamic Scheduling and Interference Mitigation

Bluetooth is a cable replacement technology for Wireless Personal Area Networks. It is designed to support a wide variety of applications such as voice, streamed audio and video, web browsing, printing, and file sharing, each imposing a number of quality of service constraints including packet loss, latency, delay variation, and throughput. In addition to QOS support, another challenge for Bluetooth stems from having to share the 2.4 GHz ISM band with other wireless devices such as IEEE 802.11. The main goal of this paper is to investigate the use of a dynamic scheduling algorithm that guarantees QoS while reducing the impact of interference. We propose a mapping between some common QoS parameters such as latency and bit rate and the parameters used in the algorithm. We study the algorithm's performance and obtain simulation results for selected scenarios and configurations of interest.     

Throughput study for admission control in IEEE 802.11 DCF with ARF

We propose an analytical approach to determining the admission of new stations to a WLAN operating in IEEE 802.11 Distributed Coordination Function (DCF) with Auto Rate Fallback (ARF). The proposed approach is based on a cross layer analytical model of how the throughput of existing stations in the WLAN is affected by admitting the new station in non-saturated as well as saturated traffic conditions. The effectiveness of the proposed approach is verified by simulations.     

Bluetooth and WLAN coexistence: challenges and solutions

In this article we discuss solutions to the interference problem caused by the proximity and simultaneous operation of Bluetooth and WLAN networks. We consider different techniques that attempt to avoid time and frequency collisions of WLAN and Bluetooth transmissions. We conduct a comparative analysis of their performance, and discuss the trends and trade-offs they bring for different applications and interference levels. Performance is measured in terms of packet loss, TCP goodput, delay, and delay jitter.     

A priority scheme for the IEEE 802.14 MAC protocol for hybridfiber-coax networks

In order to support quality-of-service (QoS) for real-time data communications such as voice, video and interactive services, multiaccess networks must provide an effective priority mechanism. The context of this work is the IEEE 802.14 standard for hybrid fiber coaxial (HFC) networks which has a shared upstream channel for transmissions from stations to the headend. This work presents a multilevel priority collision resolution scheme, which separates and resolves collisions between stations in a priority order, thereby, achieving the capability for preemptive priorities. We present a set of simulation scenarios which show the robustness and efficiency of the scheme, such as its ability to isolate higher priority traffic from lower priorities and to provide quick access to high-priority requests. In March 1998, a framework for handling priorities in the collision resolution process, which adopts a semantics similar to the semantics of our scheme, was included in the 802.14 standard     

A probabilistic call admission control algorithm for WLAN in heterogeneous wireless environment

In an integrated WLAN and cellular network, if all mobile users whose connections originate in the cellular network migrate to the WLAN whenever they enter the double coverage area, the WLAN will be severely congested and its users will suffer from performance degradation. Therefore, we propose a Call Admission Control (CAC) algorithm that allows the WLAN to limit downward Vertical Handovers (VHOs) from the cellular network to reduce unnecessary VHO processing. Numerical and simulation results demonstrate that our CAC scheme reduces the unnecessary VHO processing while keeping the DVHO blocking rate within acceptable limits and maintaining reasonable throughput in the WLAN.     

Performance Metrics for IEEE 802.21 Media Independent Handover (MIH) Signaling

The IEEE 802.21 Media Independent Handover (MIH) working group is developing a set of mechanisms to facilitate migration of mobile users between access networks that use different link-layer technologies. Among these are mobility managers that create and process signaling messages to facilitate handovers. The MIH signaling architecture being developed in the Internet Engineering Task Force (IETF) allows any transport layer protocol to carry MIH messages. The IETF has considered using the unreliable but lightweight transport available with the User Datagram Protocol (UDP) as well as the reliable stream-oriented transport with congestion control offered by the Transmission Control Protocol (TCP). In this paper we develop mathematical models that result in expressions for the characteristic function of the time required to complete exchanges of an arbitrary number of MIH signaling messages between a mobile node (MN) and a remote mobility manager (MM). Our models also provide expressions for the average amount of overhead associated with MIH message exchanges due to retransmissions either by the MIH signaling entities or by the transport-layer protocol. In addition, we provide simulation results that confirm the results from the mathematical model and illustrate the effect of varying transport parameters such as the TCP maximum retransmission timeout.