Shoubao Yang

Collaborative SCTP: a collaborative approach to improve the performance of SCTP over wired-cum-wireless networks

Stream control transmission protocol (SCTP) is one of the latest transport layer protocols. It is equipped with many new features, such as multi-stream and multi-homing, and still maintains TCP-like congestion control mechanisms. Like TCP, SCTP fails to differentiate wireless loss from congestion loss, thus its performance over wired-cum-wireless networks suffers from unnecessary congestion window decreases. To improve the performance of SCTP in such a scenario, a new approach with the collaboration of multiple entities and interaction of multiple network layers is proposed. Simulation experiments, conducted through extended ns-2, validated that the proposed approach is adaptive to the variable bit error rate (BER) of the wireless channel, and can achieve higher goodput along with higher bandwidth utilization efficiency.

A Mac-error-warning method for SCTP congestion control over high BER wireless network

The problem of high BER (bit error rate) usually plagues the wireless connection, especially for some real time applications such as VoIP (voice over IP) and some military uses. The newly developed transport layer protocol SCTP (stream control transmission protocol) also has to face this problem. Though equipped with many new features, SCTP congestion control mechanism fails to distinguish wireless loss from congestion loss, thus its performance over high BER wireless network suffers from unnecessary congestion window decreasing. To improve the performance of SCTP in such a scenario, a Mac-error-warning method is proposed in this paper. Simulation experiments conducted through extended ns-2 validated that the proposed method could achieve higher throughput. The throughput improvement arrives at 946.22% when BER is 0.0005.

Directional Double Metric Routing in Wireless Mesh Network

Due to unstable link states, broadcasting transmission pattern, and interference between neighbor nodes, routing in wireless mesh network (WMN) is much more complicated and unpredictable than wired network. As the simplest and most primitive routing metric, hop count does not always work well in WMN where routing with least hop count does not bring the best performance. Recent research shows that radio metrics, such as ETX, ETT, etc., work better in routing in wireless mesh network than hop count. These metrics reflect more accurately the link conditions in a mesh network in terms of delay, loss, bandwidth, and so on. However, to our best knowledge one thing, the asymmetry in a wireless link has been neglected the routing protocols developed so far. We propose a double metric routing method with a cross-layer design taking the asymmetry of a wireless link into account, in which monitoring and measurement functions provide metrics in both forward and reverse directions and captures the link state between the node and each of its neighbors. Applying this method to AODV, directional double metric AODV is proposed. By one single route discovering operation the proposed AODV-DDM finds two different paths based on the radio metrics in the forward and reverse directions, from source to destination and from destination to source respectively. Applications with asymmetrical traffic between source and destination are expected to benefit much from the results of this research.

A Fair Rate-Balance link Scheduling in WiMAX Mesh network

In order to ensure the fairness of links and network stability, this paper analyzes the link scheduling model in WiMAX Mesh network and proposes a Fair Rate-Balance link Scheduling scheme (FRBS). FRBS calculates the scheduling parameter <Dx, p> under stability constraint making the arrival data rate of the link equal to outgoing rate. At the grant step, FRBS assigns bandwidth using a max-min fair Round Robin algorithm for link fairness. Simulation results show that FRBS has much better performance than the greedy scheduling in both light load and heavy load network.

Multi-gateway multi-path routing protocol for 802.11s WMN

Wireless mesh networks usually deploy multiple gateways to enhance the capacity. This paper studies how to maintain forwarding paths in 802.11s wireless mesh network. A Multi-Gateway Multipath routing protocol (MGMP) is proposed to explore path diversity. MGMP constructs multiple paths between source and destination using a proactive tree architecture as HWMP. In order to make MGMP more efficient, three optimized heuristics are discussed by simulation. Our ns-2 experiment results show that MGMP consistently outperforms three representative routing protocols, HWMP, AODV and OLSR. Especially MGMP gives 12.8% throughput gain and reduces routing overhead to 20% compared with HWMP.

A Link Level Load-Aware Queue Scheduling algorithm on MAC layer for wireless mesh networks

A Link Level Load-Aware Queue Scheduling algorithm (LLLAQS) on MAC layer is proposed in this paper in order to suppress the data transmission on congested links and balance the load in the wireless mesh networks. The algorithm not only takes the load on the congested node into consideration but also differentiates the congested links and non-congested links. By scheduling the traffic on the non-congested or light-congested links for a congested node, the proposed algorithm can balance the traffic load more smartly than the traditional queue scheduling schemes. The simulation results in NS2 show that our queue scheduling algorithm outperforms other existing queue scheduling algorithms in terms of the network throughput, the average delay, and the drop ratio.

A new parallel scheduling system for multiple radio wireless mesh network

To enhance the capacity of wireless mesh networks, a key technique is widely investigated which is the usage of multi-radio and multi-channel diversity. In this paper, a new parallel scheduling system is proposed which exploits MAC diversities by transmitting packets on the radios opportunistically. Compared with conventional packet transmission which follows “one flow one radio”, the new system uses radio diversity to transmit the packets on different radios simultaneously. Two kernel components of this system are selection module and schedule module. A localized selecting algorithm is implemented in the selection model to choose the right radios based on the quality of wireless links; two distributed packet-scheduling algorithms are optional with the schedule component. Finally, a routing metric adapting this system is presented. We have carried out a comprehensive performance evaluation of this system using ns-2. Simulation results show that it can successfully harness diversity of multi-radio and multi-channel to provide considerable improvements over a baseline multi-channel system in several situations.

Interface function adaptive channel assignment in multi-radio wireless mesh networks

Reasonable channel assignment is one of the key research contents of the multi-channel assignment algorithms. A distributed channel assignment method based on partition of interface function was proposed in this paper. Different channel assigning or switching algorithms for interfaces with different function were used: Channel assigning algorithm based on measuring time to gateway was used for station interfaces while peer-assisted channel assignment algorithm was used for AP interfaces. Simulation results show that this method can greatly improve network throughputs under high network loads especially.