Meejeong Lee

mSCTP for soft handover in transport layer

In this letter, we discuss mobile Stream Control Transmission Protocol (SCTP) for soft handover in the transport layer. From the experimentations on triggering rules for Add-IP and Primary-Change during the handover, it is shown that the aggressive Add-IP and conservative Primary-Change rules provide better throughput.

An end-to-end multipath smooth handoff scheme for stream media

Supporting transmission of stream media over wireless mobile networks is often difficult because packets may be lost due to the rerouting of packets during handoff, and also because bursts of packet loss may occur during handoff due to the disparity in the amount of available bandwidth among different cells. In this paper, we propose an end-to-end multipath handoff scheme that provides smooth handoff for stream media in wireless networks with different amounts of available bandwidth from cell to cell. In the proposed scheme, multiple paths are established during handoff to reach a mobile destination node. The stream media sources are equipped with an adaptive multilayer encoder, and important layers in the encoded video stream are duplicated and transmitted over multiple paths during handoff. The effectiveness of the proposed multipath handoff scheme is verified and compared with existing schemes through extensive simulations. The simulation results show that the proposed scheme provides higher throughput and better quality for stream media.

PatchODMRP: an ad-hoc multicast routing protocol

We propose an ad-hoc multicast routing protocol, referred to as PatchODMRP. PatchODMRP extends the ODMRP (on-demand multicast routing protocol), which is a mesh-based multicast routing protocol proposed for ad-hoc networks. In ODMRP, the nodes that are on the shortest paths between the multicast group members are selected as forwarding group (FG) nodes, and form a forwarding mesh for the multicast group. The ODMRP reconfigures the forwarding mesh periodically to adapt it to the node movements. When the number of sources in the multicast group is small, usually the forwarding mesh is formed sparsely and it can be very vulnerable to mobility. In this case, very frequent mesh reconfigurations are required in ODMRP, resulting in a large control overhead. To deal with this problem in a more efficient way, PatchODMRP deploys a local patching scheme instead of having very frequent mesh reconfigurations. In PatchODMRP, each FG node keeps checking if there is a symptom of mesh separation around itself. When an FG node finds such a symptom, it tries to patch itself to the mesh with local flooding of control messages. Through a course of simulation experiments, the performance of PatchODMRP is compared to the performance of ODMRP. The simulation results show that PatchODMRP improves the data delivery ratio, and reduces the control overheads. It has also been shown that the performance gain is larger when the degree of node mobility is bigger.

Feedback control mechanisms for real-time multipoint video services

While existing research shows that reactive congestion control mechanisms are capable of providing high video quality and channel utilization for point-to-point real-time video, there has been relatively little study of the reactive congestion control of point-to-multipoint video, especially in ATM networks. Problems complicating the provision of multipoint, feedback-based real-time video service include: (1) implosion of feedback returning to the source as the number of multicast destinations increases and (2) variance in the amount of available bandwidth on different branches in the multipoint connection. A new service architecture is proposed for real-time multicast video, and two multipoint feedback mechanisms to support this service are introduced and studied. The mechanisms support a minimum bandwidth guarantee and the best effort support of video traffic exceeding the minimum rate. They both rely on adaptive, multilayered coding at the video source and closed-loop feedback from the network in order to control both the high and low priority video generation rates of the video encoder. Simulation results show that the studied feedback mechanisms provide, at the minimum, a quality of video comparable to a constant bit rate (CBR) connection reserving the same amount of bandwidth. When unutilized network bandwidth becomes available, the mechanisms are capable of exploiting it to dynamically improve video quality beyond the minimum guaranteed level.

Connectivity restoration in a partitioned wireless sensor network with assured fault tolerance

Wireless sensor network (WSN) applications, especially those serving in inhospitable environments such as battlefield reconnaissance, are susceptible to large-scale damage which usually causes simultaneous failure of multiple collocated sensors and gets the network divided into disjoint partitions. In order to prevent the WSN from being inoperative, restoring the overall network connectivity is crucial. Furthermore, it may be desirable to make the repaired network topology resilient to future single node failures caused by aftermath. In this paper, we present an effective strategy for achieving such recovery goal by establishing a bi-connected inter-partition topology while minimizing the maximum path length between pairs for partitions and deploying the least count of relay nodes (RNs). Finding the optimal number and position of RNs is NP-hard and we thus pursue heuristics. The proposed Connectivity Restoration with Assured Fault Tolerance (CRAFT) algorithm strives to form the largest inner simple cycle or backbone polygon (BP) around the center of the damaged area where no partition lies inside. RNs are then deployed to connect each outer partition to the BP through two non-overlapping paths. We analyze the properties of CRAFT mathematically and validate its performance through extensive simulation experiments. The validation results show that CRAFT yields highly connected topologies with short inter-partition paths while employing fewer RNs than competing schemes.

Adaptive load distribution over multipath in NEPLS networks

The emergence of multiprotocol label switching (MPLS) with its efficient support of explicit routing provides basic mechanisms for facilitating traffic engineering. Exploiting this capability of MPLS, we propose an adaptive multipath traffic engineering mechanism named LDM (load distribution over multipath). The main goal of LDM is to enhance the network utilization as well as the network performance by adaptively splitting traffic load among multiple paths. LDM takes pure dynamic approach not requiring any a priori traffic load statistics. Routing decisions are made at the flow level, and traffic proportioning reflects both the length and the load of a path. LDM also dynamically selects a few good label switched paths (LSPs) according to the state of the entire network. We use simulation to compare the performance of LDM with the performance of several representative dynamic load distribution approaches as well as the traditional static shortest path only routing. The numerical results show that LDM outperforms the compared approaches in both the blocking ratio as well as the performance of the accepted traffic flows.

Dynamic Load Distribution in MPLS Networks

Exploiting the efficient explicit routing capability of MPLS, we propose a dynamic multipath traffic engineering mechanism named LDM(Load Distribution over Multipath). The main goal of LDM is to enhance the network utilization as well as the network performance by adaptively splitting traffic load among multiple paths. LDM makes decisions at the flow level, and distribute traffic based on both the length and the load of a path. LDM also dynamically selects a number of good Label Switched Paths (LSPs) for traffic delivery according to the state of the entire network. We use simulation to compare the performance of LDM with the performance of several representative dynamic load distribution approaches as well as the traditional static shortest path only routing. The numerical results show that LDM outperforms the compared approaches in both the blocking ratio as well as the performance of the accepted traffic flows.

An end-to-end multi-path smooth handoff scheme for stream media

Supporting transmission of stream media over wireless mobile networks is often difficult because packets may be lost due to the rerouting of packets during handoff, and also because bursts of packet loss may occur during handoff due to the disparity in the amount of available bandwidth among different cells. In this paper, we propose an end-to-end multipath handoff scheme that provides smooth handoff for stream media in wireless networks with different amounts of available bandwidth from cell to cell. In the proposed scheme, multiple paths are established during handoff to reach a mobile destination node. The stream media sources are equipped with an adaptive multilayer encoder, and important layers in the encoded video stream are duplicated and transmitted over multiple paths during handoff. The effectiveness of the proposed multipath handoff scheme is verified and compared with existing schemes through extensive simulations. The simulation results show that the proposed scheme provides higher throughput and better quality for stream media.

A Transport Layer Mobility Support Mechanism

Recently, mobile SCTP (mSCTP) has been proposed as a transport layer approach for supporting mobility. mSCTP is based on the ’multi-homing’ feature of Stream Control Transmission Protocol (SCTP), and utilize the functions to dynamically add or delete IP addresses of end points to or from the existing connection in order to support mobility. In this paper, we propose a mechanism to determine when to add or delete an IP address, utilizing the link layer radio signal strength information in order to enhance the performance of mSCTP. We also propose a mechanism for a mobile node to initiate the change of data delivery path based on link layer radio signal strength information. The simulation results show that the performance of proposed transport layer mobility support mechanism is competitive compared to the traditional network layer mobility supporting approach. Especially, when the moving speed of mobile node is fast, it shows better performance than the traditional network layer approach.

Light-Weight Reliable Broadcast Message Delivery for Vehicular Ad-Hoc Networks

Reliability as well as efficiency of transmissions is of a paramount issue for the safety critical services of VANET due to the urgency and/or significance of the messages. To this end,various retransmission mechanisms have been studied for reliable broadcast message delivery in VANETs. Most of the existing approaches, though, rely on periodic beacons for retransmission decisions and intrinsically require high control overheads. Especially, in urban environments where the traffic density tends to be high, minimizing control overheads is important not only for the efficiency but also for the reliability of user message delivery. In this paper, we propose an efficient broadcast message delivery mechanism, which does not rely on the periodic beacon exchanges. Based on the observation that the broadcast message delivery could be particularly difficult at the intersections due to the signal diffraction and attenuation caused by the obstacles such as buildings around the corners of the intersection, a novel mechanism to make efficient and effective retransmissions across an intersection is proposed. Simulation results show that the proposed mechanism can provide similar or better reliability while incurring prominently less overheads than the existing approaches.