Zhi Li

QRON: QoS-aware routing in overlay networks

Recently, many overlay applications have emerged in the Internet. Currently, each of these applications requires their proprietary functionality support. A general unified framework may be a desirable alternative to application-specific overlays. We introduce the concept of overlay brokers (OBs). We assume that each autonomous system in the Internet has one or more OBs. These OBs cooperate with each other to form an overlay service network (OSN) and provide overlay service support for overlay applications, such as resource allocation and negotiation, overlay routing, topology discovery, and other functionalities. The scope of our effort is the support of quality-of-service (QoS) in overlay networks. Our primary focus is on the design of QoS-aware routing protocols for overlay networks (QRONs). The goal of QRON is to find a QoS-satisfied overlay path, while trying to balance the overlay traffic among the OBs and the overlay links in the OSN. A subset of OBs, connected by the overlay paths, can form an application specific overlay network for an overlay application. The proposed QRON algorithm adopts a hierarchical methodology that enhances its scalability. We analyze two different types of path selection algorithms. We have simulated the protocols based on the transit-stub topologies produced by GT-ITM. Simulation results show that the proposed algorithms perform well in providing a QoS-aware overlay routing service.

HostCast: a new overlay multicasting protocol

Though the merits of IP-based multicast are undeniable, the deployment of IP multicast has met many difficulties. In the past several years, lots of research works have been done on overlay multicast. In this paper, we propose a new overlay multicast protocol: HostCast. Besides constructing a data delivery tree, HostCast uses a simple and efficient approach to form an overlay mesh for control and maintenance. The mesh can effectively facilitate the overlay multicasting. HostCast improves the reliability of overlay multicast tree and decreases the convergence time as demonstrated by the results obtained via simulation.

On investigating overlay service topologies

Recently, a moderate amount of work has been reported on the use of overlay networks to support value-added network services, such as multicasting, Quality-of-Service (QoS), security, etc. To design an overlay network, the first step is to choose an overlay topology connecting all the overlay service nodes. When considering overlay topologies, several questions need to be answered first: How overlay topologies affect overlay routing performance? Which topologies can provide satisfactory performance? How can we construct efficient overlay topologies connecting all the overlay nodes? n nIn this paper, we focus on the overlay network topology construction issue. First, we evaluate and compare the performance and overhead of the existing overlay topologies. Second, we formalize the overlay topology construction problem and propose two new heuristic methods to construct efficient overlay topologies. Simulation results have demonstrated the efficiency of the two proposed approaches. It is shown that overlay service performance varies significantly with respect to different overlay topologies. Thus, it is important to choose an appropriate overlay network topology. The knowledge of IP-layer topology information also benefits significantly in constructing efficient overlay topologies as inferred from the results.

Adaptive per hop differentiation for end-to-end delay assurance in multihop wireless networks

As the rapid growth of smart hand-held devices, multihop wireless access networks have a lot of potential applications in a variety of fields in civilian and military environments. Many of these applications, such as realtime audio/video streaming, will require some form of end-to-end QoS assurance. In this paper, we present an adaptive per hop differentiation (APHD) scheme towards achieving end-to-end delay assurance in multihop wireless networks. Our scheme is based on EDCA technique which is proposed in 802.11e draft. In EDCA, data packets of different priorities will use different MAC contention parameter set, which translate into different delays. Our APHD scheme extends the capability of EDCA into multihop environment by taking end-to-end delay requirement into consideration at each intermediate hop. Following a cross-layer design approach, APHD is aimed to be a distributed and localized technique. Individual nodes keep track of the channel state independently without any intercommunication overhead. Data packets carry end-to-end delay requirement along with other important information in the packet header. At an intermediate node, based on data packets end-to-end requirement, its accumulative delay so far, and the current nodes channel status, APHD smartly adjusts data packets priority level in order to satisfy its end-to-end delay requirement. Simulation results show that APHD scheme can provide excellent end-to-end delay assurance while achieving much higher network utilization, compared to a pure EDCA scheme.

QoS-aware multicasting in DiffServ domains

QoS-aware multicasting is becoming more and more desirable with the expanding usage of group-based applications, especially those involving multimedia objects. Until now, most of the proposed QoS-aware multicasting routing protocols adopt per-flow based resource reservation. Although these schemes can be adopted in integrated services (IntServ) Internet, they are not suitable for more scalable Differentiated Services (DiffServ) Internet. A new QoS-aware multicast routing protocol called QMD is proposed for DiffServ environments in this paper. Based on the design philosophy of DiffServ, the complex multicasting control plane functionalities are removed from the core routers. In addition, for each multicast group, only a limited set of on-tree routers (termed as key nodes) maintain multicast routing states and forward multicast data traffic. The key nodes of a multicast group uniquely identify a QoS-satisfied multicast tree connecting the group members. Although the other on-tree routers between any two key nodes do not maintain any multicast routing states and QoS reservation information, the group members QoS requirements can still be satisfied. Through simulation experiments based on both random and real intra-domain topologies, we have also demonstrated that QMD can provide higher QoS-satisfaction rate while maintaining the simplicity of core routers.

On the analysis of overlay failure detection and recovery

Application-layer overlay networks have been proposed as an alternative method to overcome IP-layer path anomalies and provide users with improved routing services. Running at the application layer, overlay networks usually rely on probing mechanisms for IP-path performance monitoring and failure detection. Their service performance is jointly determined by their topology, parameters of probing mechanism and failure restoration methods. In this paper, we first define metrics to evaluate the performance of overlay networks in terms of failure detection and recovery, network stability and overhead. Second, we model the overlay-based failure detection and recovery process. Through extensive simulations, we investigate how different IP-layer path failure characteristics and overlay topologies, detection and restoration parameters affect service performance of overlay networks. In particular, we examine the tradeoffs among different overlay performance metrics and the optimal performance conditions. Our study helps to understand overlay-based failure recovery and provides practical guidance to overlay network designers and administrators.

APHD: End-to-End Delay Assurance in 802.11e Based MANETs

In this paper we present an adaptive per hop differentiation (APHD) scheme towards achieving end-to-end delay assurance in multihop wireless networks. Our APHD scheme extends the capability of IEEE 802.11e EDCA technique into multihop environments by taking end-to-end delay requirement into consideration. At an intermediate node, based on data packets end-to-end requirement, its accumulative delay so far, and the current nodes channel status, APHD smartly adjusts a data packets priority level in order to satisfy its end-to-end delay requirement Simulation results show that APHD scheme can provide excellent end-to-end delay assurance while achieving much higher network utilization, compared to a pure EDCA scheme

Virtual multi-homing: on the feasibility of combining overlay routing with BGP routing

This paper proposes a framework called Virtual Multi-Homing (VMH) to achieve loose source-based path selection and improve inter-domain path diversity. VMH is based on the concept of Virtual Peering and Multi-Homing Overlay to set up flexible inter-domain relationships. By interacting with BGP whenever possible, VMH can achieve scalable inter-domain route discovery without introducing duplicate work. In addition, VMH is a complementary approach to the existing Internet routing infrastructure and can be incrementally deployed.

QMBF: a QoS-aware multicast routing protocol

Many multicast applications, such as video-on-demand and tele-education, desire quality of service (QoS) support from the underlying network. Recently, many QoS-based multicast protocols have been proposed to meet this requirement. However, few of them can achieve high success ratios while maintaining good scalability. In this paper, we propose a new QoS-aware multicast protocol based on a bounded flooding technique (QMBF). In this protocol, every network node maintains the knowledge of a local network cell (LNC) topology as well as QoS state information (collected from the bounded flooding messages). QMBF utilizes this knowledge to increase the probability and accuracy of finding a feasible branch which connects a new member to an existing multicast tree. The protocol exploits two approaches to find feasible branches: repeatedly computing partial feasible branches using the LNC information and searching multiple paths. The design of QMBF allows it to operate on top of any unicast routing protocol or cooperate with a QoS-based unicast routing protocol. Results obtained using NS-2 simulator demonstrate high success ratio for locating feasible branches for multicast paths.

QoS-aware multicast protocol using bounded flooding (QMBF) technique

Many multicast applications, such as video-on-demand and tele-education have quality of service (QoS) requirements from the underlying network. Recently, many QoS-based multicast protocols have been proposed to meet these requirements. However, few of them can achieve high success ratios. We propose a new QoS-based multicast protocol, QoS-aware multicast protocol using bounded flooding (QMBF) technique. Every network node has local network cell topology information as well as QoS state information. The QMBF utilizes this information to increase the chance of finding the feasible branch. It is based on two methods to find a feasible branch - computing out partial feasible branches using local network cell information (collected from bounded flooding messages) and multiple path searching. The design of QMBF allows it to operate on top of any unicast routing protocol or cooperate with a QoS-based unicast routing protocol.