Jong Ok Kim

MAC-level measurement based traffic distribution over IEEE 802.11 multi-radio networks

It is expected that multiple radio access technologies coexist within a single terminal. In those networks, we focus on the problem of how to distribute IP traffic into multiple underlying links in order to enhance the overall aggregated throughput. As an effective aggregation mechanism, traffic is equivalently assigned to each link, in proportion to its available capacity. To this end, the capacity of each link is commonly measured for easy comparison between radio links, and then, the relative split ratio is accordingly determined. We identify LTT (link transmission time) as a common link resource measure. We specifically consider that each terminal is equipped with IEEE 802.11a and 802.11b devices, and have implemented a practical testbed network system. In IEEE 802.11 networks, LTT is considerably variable due to random back-off process, depending on neighboring contending terminals and radio signal quality variations. It is actually captured at a radio device driver instead of theoretical calculation. Based on measurements, we determine traffic split ratios to both links. Extensive experimental results show that the proposed method could reduce the packet reorder delay at the receiver by achieving equal load-balance, rapidly adapting to varying link qualities (i.e., channel access contention and radio signal attenuation).

Airtime-based Link Aggregation at the Co-Existence of WiMAX and WiFi

For multi-access networks with heterogeneous radio access techniques, the challenges include the problem of how to optimally distribute network traffics into each radio link in order to enhance the aggregated link capacity. As an effective load balance mechanism, traffics may be equivalently assigned to each RA, in proportion to its available capacity. To this end, airtime cost is identified as a common resource measure for WiMAX and WiFi links. Due to their different data transmission mechanisms, the calculation of airtime cost is separately derived. Based on the common metric, the offered traffic for each link is converted into airtime cost required for its transmission. Traffics are distributed so that cumulative airtime cost between RAs is fair. Evaluation results show that airtime cost model can commonly measure the link resources of heterogeneous wireless links, and this measurement enables traffics to be equally distributed, in proportion to their transmission capacity.

Evaluation of Linux Bonding Features

The paper contains an evaluation of the current Linux bonding implementation for wired interfaces. The Linux bonding provides methods to aggregate multiple wired interfaces to support load balancing, fault-tolerance and throughput improvement. The intention is to identify the performance of the current Linux bonding implementation and to use the results and assumptions for future discussions about bonding of wireless interfaces. The paper presents details about interface bonding in a RedHat Linux system and discusses measurement results of two bonded LAN interfaces using the round-robin bonding mode.

Splitting downlink multimedia traffic over WiMAX and WiFi heterogeneous links based on airtime-balance

We investigate the challenge of splitting a traffic flow over WiMAX and WiFi links. For traffic load distribution over heterogeneous RATs (Radio Access Technologies), heterogeneous link resources need to be commonly measured and fairly compared. To this end, an airtime cost model is considered as a common resource measure. The model can be used to estimate channel time consumed for a successful packet transmission. As a traffic split mechanism, an airtime-balance method is proposed. Using the airtime cost model, the offered traffic load (in Mbps) is converted into airtime cost required for its transmission, and IP packets are distributed to multiple RATs so that airtime is equally balanced between RATs. n nWe have implemented a practical test-bed system, including both WiMAX and WiFi systems, and used it to conduct extensive experiments indoor and outdoor. Experimental results confirm that airtime-balance can achieve an improved flow split to reduce the waiting packets at the reorder buffer of the receiver. Moreover, it could realize a more rapid adaptation to link variations with local measurements, when compared to the RTT-based method, which also requires extra system overhead due to the use of probe packets. Copyright

Delay-Sensitive Retransmission Method Based on Network Coding in IEEE 802.11 Wireless LANs

Recently, network coding (NC) has been popularly applied to wireless networks in order to improve channel utilization. In wireless LANs, when NC is applied to packet retransmission, a base station can simultaneously retransmit multiple packets destined to different wireless stations for a single retransmission trial. On the other hand, NC creates additional packet delay at both base station and wireless stations, and hence, packet transfer delay may increase seriously. However, existing NC-based retransmission methods do not consider this additional delay explicitly. In addition, when the number of flows is small, NC exhibits less benefits because the chances of NC-based retransmission are highly reduced. Therefore, in this paper, we propose a novel NC-based retransmission method in order to improve packet transfer delay and jitter of received packets. Moreover, to achieve further improvement of delay, jitter and retransmission efficiency, we propose a retransmission method in which NC-based retransmission cooperates with the typical ARQ method. We overcome the disadvantage of NC-based retransmission by combining with ARQ cooperatively. Finally, we show the effectiveness of the proposed methods by extensive computer simulation.

Field Trial on Cognitive Radio Technology: Adaptive Co-Use of Heterogeneous Wireless Media on Multiple Base Stations

As advanced integrated network architecture, cognitive radio technologies, which aim to improve the spectrum efficiency, have been studied. In the cognitive radio networks, each node recognizes radio conditions, and according to them, optimizes their wireless communication routes with the integration of the heterogeneous wireless media not only by switching over them but also aggregating and utilizing them simultaneously. The Adaptive control of switchover use and concurrent use of various wireless media will offer a stable and flexible wireless communication. In this paper, we introduce our cognitive radio testbed that has IEEE802.16 and IEEE802.11 interfaces, and perform the field trial in order to experimentally examine the effectiveness of the cognitive radio technologies. The experimental results show that the concurrent use of IEEE802.16 and IEEE802.11 wireless media offers high IP throughput performance and furthermore, the adaptive route control according to the radio conditions improves the IP throughput by more than 20% and reduce the one-way delay to less than 1/6. It is found that the cognitive radio technologies can provide the appropriate wireless communication routes to meet various demands for application QoS.

Optimal Packet Allocation with Airtime Constraint for Multi-Access Links

In next generation wireless networks, a variety of heterogeneous radio access technologies are expected to be available simultaneously within a single wireless terminal. This paper addresses the challenge of link aggregation in multi-access networks, where a key issue is how to optimally aggregate bandwidth offered by the individual radio link. Effective link throughput model is employed as a common resource measure for heterogeneous links. Based on the model, we present a packet allocation technique to optimize link aggregation. The mapping of packets to radio access links is performed to maximize the overall expected system throughput. Airtime constraint is added for an equal load balance. We have conducted extensive simulations with two scenarios. One is at the co-existence of WiMAX and WiFi, and the other includes only WiFi links. The proposed technique adaptively operates to time-varying link resource, and achieves better the aggregated link performance than WRR with fixed distribution ratio.

Adaptive Multimedia Flow Splitting over WiMAX and WiFi Links

To meet the bandwidth requirements of multimedia services, multipath transmission is a promising solution. In this paper, we consider multi-access networks, where WiMAX and WiFi links are set up at the same time. Multipath transmission suffers from the intrinsic problem of out-of-order packet delivery. This has an adverse impact on TCP and even UDP-based delay sensitive applications. However, multimedia streaming services allow some tolerance to transmission delay. Motivated by this observation, we investigate how to split multimedia flows over heterogeneous links. Wireless link capacity varies widely over time due to dynamic radio conditions. The capacity variations should be promptly reflected in traffic splitting in order to accomplish an equal load-balance. A practical prototype system has been implemented. We have performed extensive measurements from a prototype system. Through practical experimental results, we could verify two major research goals. One is that multimedia splitting can improve the overall network performance (e. g., the permitted multimedia sessions or the aggregated bandwidth) while still keeping an acceptable media quality. The other is an adaptation capability to varying link quality. It has been widely investigated under various radio conditions and different monitoring intervals. It is shown that the adaptive technique is effective under dynamic radio environments.

QoS-Aware Retransmission with Network Coding Based on Adaptive Cooperation with IEEE 802.11e EDCA

Recently, network coding (NC) has been popularly applied to wireless networks in order to improve scarce wireless capacity. In wireless LANs, NC can be applied to packet retransmission in which multiple packets can be equivalently transmitted by a single retransmission trial at base station (BS). In this paper, retransmission based on NC cooperates with IEEE 802.11e EDCA. In EDCA, when network load is high, QoS is significantly degraded even in high priority class. To solve this, existing methods improve backoff control, and decrease packet loss caused by collision. However, backoff control cannot prevent packet loss caused by multipath channel fading. In the proposed cooperation between NC and EDCA, QoS of high priority class is improved from the aspect of efficient loss recovery. Unlike NC method with no QoS control, we encounter transmission scheduling problem among NC packet, single lost packet, and new packet. Moreover, in the constitution of packets encoded into NC packet, priority and traffic load of each priority class should be considered. Therefore, we propose how to determine the packet to be transmitted at next transmission opportunity in BS and how to constitute NC packets encoded by adequate set of lost packets. Finally, we show the effectiveness of the proposed method by extensive computer simulation.

Retransmission method with Network Coding based on reordering delay in wireless LAN

Recently, Network Coding (NC) has been popularly applied to wireless networks in order to improve channel utilization. In wireless LANs, when NC is applied to packet retransmission, a base station can simultaneously retransmit multiple packets destined to different wireless stations for a single retransmission trial. On the other hand, at a receiver side, out-of-order packet reception can occur, and the additional reordering process is required. However, existing NC-based retransmission methods do not consider this reordering delay explicitly, hence packet transfer delay may increase seriously. Therefore, in this paper, we propose a novel NC-based retransmission method considering packet reordering delay in order to improve packet transfer delay and jitter of received packets. Finally, we show the effectiveness of the proposed method by computer simulation.