An efficient traffic management framework for multi-channel wireless backbone networks

Transcription

1 An efficient traffic management framework for multi-channel wireless backbone networks Yuzo Taenaka 1a) and Kazuya Tsukamoto 2 1 Information Technology Center, The University of Tokyo Yayoi, Bunkyo, Tokyo , Japan 2 Dept. of Computer Science and Electronics, Kyushu Institute of Technology Kawazu, Iizuka, Fukuoka, , Japan a) taenaka@nc.u-tokyo.ac.jp Abstract: This paper presents a traffic management framework for multi-channel wireless backbone network (WBN). To date, WBNs are not allowed to flexibly use multiple channels even if there are many vacant channels. Furthermore, the limited available channel(s) are not utilized effectively. Therefore, we propose a virtual AP enabling to handle the unlimited number of channels potentially, and then present a traffic control framework with OpenFlow, which freely controls traffic on multiple channels. Experimental results show that WBN linearly increases the network capacity according to the increase in the number of channels. That is, effective utilization of multi-channel can be achieved. Keywords: effective channel utilization, multiple channels, traffic control framework, OpenFlow, wireless backbone network Classification: Internet References [1] P. H. Pathak and R. Dutta, A Survey of Network Design Problems and Joint Design Approaches in Wireless Mesh Networks, IEEE Communications Surveys and Tutorials, vol. 13, no. 3, pp , [2] D. Benyamina, A. Hafid, and M. Gendreau, Wireless Mesh Networks Design - A Survey, IEEE Communications Surveys and Tutorials, vol. 14, no. 2, pp , [3] E. Alotaibi and B. Mukherjee, A Survey on Routing Algorithms for Wireless Ad-Hoc and Mesh Networks, Computer Networks, vol. 56, no. 2, pp , Elsevier, [4] W. Si, S. Selvakennedy, and A. Y. Zomaya, An Overview of Channel Assignment Methods for Multi-radio Multi-channel Wireless Mesh Networks, Journal of Parallel and Distributed Computing, vol. 70, no. 5, pp , Elsevier, May [5] K. S. Vijayalayan, A. Harwood, and S. Karunasekera, Distributed Scheduling Schemes for Wireless Mesh Networks: A Survey, ACM Computing Survey, vol. 46, no. 1, pp. 14:1 14:34, July

2 [6] J. So and N. H. Vaidya, Multi-channel Mac for Ad Hoc Networks: Handling Multi-channel Hidden Terminals Using a Single Transceiver, Proc. MobiHoc, Tokyo, Japan, pp , May Introduction Wireless mesh network (WMN) has been already deployed in wide area (e.g., shopping mall). It is mainly consisted of two sorts of APs: gateway AP (called IGW: Internet gateway) providing the Internet reachability and other APs constructing multi-hop wireless backbone network (WBN). WMN again attracts much attention as the promising access network for emerging applications such as smart-grid communication, machine-tomachine communication, and mobile data offloading. Such kind of communication normally needs the Internet access and also the amount of traffic is going to grow drastically along with the penetration of networked devices (sensors, smart meters, and smartphones). From this trend, a way of linearly increasing the network capacity of WBN is essential. However, the network capacity of WBN significantly decreases due to interferences, collisions, and congestions in shared WBN. Most studies try to avoid such situations by means of routing protocol, channel assignment, and MAC protocol [1, 2, 3, 4, 5]. To increases the network capacity, many studies propose multi-channel routing protocols [3], which jointly works with channel assignment [4]. They basically switch paths (with different channels) based on the routing table. However, these protocols cannot simultaneously use multiple links between two neighboring APs because the routing table contains only a single link (i.e., one channel) to reach a neighbor AP. The number of channels (radios) that APs use simultaneously is basically limited due to hardware equipment. Many studies actually assume few radios of AP [4]. The studies of MAC protocol conduct frame scheduling to avoid collisions between nearby APs [5, 6]. The paper [6] proposes a MAC protocol based on channel switching with a single radio, thereby using multiple channels. However, it does not contribute to increase the network capacity due to both channel switching delay and the time-allocated manner. From the distinctive points, two problems should be addressed to increase the network capacity of WBN. One is the limitation on the number of channels APs use simultaneously. In preliminary experiments, we observed that there are many vacant channels in 5-GHz band, which means that the wireless resources cannot be used effectively. Another is under-utilization of the predetermined channels. As described before, existing studies cannot effectively and simultaneously exploit multiple channels. We then propose an efficient framework treating the unlimited number of channels. Furthermore, a multi-channel traffic management framework by exploiting OpenFlow is also presented. To the best of our knowledge, there are no studies focusing on these problems and the OpenFlow based approach. We finally implement 99

3 IEICE Communications Express, Vol.3, No.3, these frameworks in a real AP hardware/software and then demonstrate preliminary experimental results to show the effectiveness of our architecture. 2 Traffic management framework for wireless backbone network 2.1 Introduction of virtual AP handling multiple channels We propose a virtual AP (VAP) shown in Figure 1. A set of APs, each of which uses a single and different channel for WBN, is connected by back-toback Ethernet of daisy chain (B2B) and treated as a VAP handling multiple channels. As shown in Figure 1, one AP in each VAP is treated as primary AP (e.g., AP1-1) and the others are secondary APs. Both the primary and secondary APs construct WBNs on respective channels, while only the primary APs provide WLAN access to users. From this architecture, the number of channels used for WBN can be flexibly changed by increasing the number of APs for VAP. Fig. 1. Design of wireless backbone network and traffic management framework c IEICE Construction of wireless backbone network In WBN, we assume that a routing protocol identifies a route of VAP toward IGW (e.g., VAP1 VAP2... in Figure 1)1 and then all traffic 1 Routing is beyond the scope of this paper. 100

4 are transmitted over multiple channels along with the route. To achieve this, we employ OpenFlow technology because it identifies a flow based on source/destination MAC address (SRCMAC/DSTMAC), source/destination IP address (SRCIP/DSTIP), and TCP/UDP port number, and can modify the frame header and output port per flow. Specifically, an OpenFlow switch (OFS) installed on each AP controls flows based on flow entries (flow control rule) consisting of the flow definition (matching rule) and the action. The flow entries are registered to each OFS when the OFS connects with an Open- Flow controller (OFC) and/or when the OFS receives unknown packets and reports it to the OFC (packet in). In both cases, the OFC creates the flow entries based on a user-developed algorithm. That is, the OFC/OFS do not have any algorithms and do nothing by default. Therefore, to construct the OpenFlow based WBN, we need all network functions of OpenFlow needed for multi-channel WBN. 2.3 Traffic management framework based on OpenFlow We propose a traffic management framework based on OpenFlow technology. Since a single OFC can collaborate with all OFSs and totally manage all flows through the OFSs, the OFC can dynamically change flow management schemes according to the changes of the traffic condition in whole WBN. Thus, the channel utilization can be optimized by the OpenFlow based WBN. To evaluate the effectiveness of channel utilization on the OpenFlow based channel switching, we here assume static traffic pattern and implement a method multiplexing a conventional multi-hop transmission as an example traffic management. Note that we currently work on an OpenFlow based flow management scheme for dynamic traffic pattern and will publish papers in the near future. The implementation consists of flow entries for functions of (1) packet in based channel selection, (2) channel switching, (3) multi-hop transmission, (4) packet delivery to the primary AP. The entry (1) is dynamically registered to OFS at packet in, while the functions (2), (3), and (4) are static flow entries of each OFS, which are registered when an OFS connects with the OFC as shown in Figure 1 (b). In (1), when a new flow arrives at a primary AP (AP2-1), the AP reports packet in to the OFC to dynamically allocate a channel to the flow. The OFC selects a channel in turn in order of packet in arrival and accordingly registers a flow entry to the AP, which replaces the DESTMAC of a frame with the MAC address of an AP with the selected channel in the same VAP. According to the flow entry, the primary AP forwards the frame on B2B toward the AP with the DESTMAC. In case of Figure 1, the selected channel is C and DESTMAC indicates AP2-3. The entry (2) forwards the frame in B2B until reaching the destined AP and the AP forwards packets received at B2B to WBN. In (3), when receiving a packet by the radio, each AP re-sends it to the neighbor AP by the same radio as a traditional WBN does. That is, the multi-hop transmission is separately conducted on each channel. To determine the next hop in shared 101

5 IEICE Communications Express, Vol.3, No.3, WBN, each AP modifies DESTMAC at each hop. In (3), packets are delivered to the primary AP that provides WLAN to users. When receiving a frame with a DESTIP belonging to its VAP, a secondary AP forwards it toward the primary AP via B2B so that the primary AP passes it to the destination host. 3 Performance evaluation 3.1 Implementation and experimental topology Figure 2 (a) shows our experimental topology. We employ WZR-HP-AG300H of Buffalo, which has two radios (2.4 GHz and 5 GHz) and five Ethernet ports. The 5-GHz radio (IEEE802.11a) is used to construct WBN, and Ethernet ports are used for B2B and for the user access instead of WLAN to investigate WBN performance only. The OFS also connects with the OFC by Ethernet to limit effects of packet losses over the link between OFC and OFS. We place APs as shown in Figure 2 (a) and change the number of APs according to experimental scenario. Fig. 2. Preliminary experiment c IEICE Experimental results We first evaluate the basic performance of WBN managed by OpenFlow. We prepare two sorts of WBNs: one is the OpenFlow based WBN and another is the static route based traditional WBN. Both WBNs are constructed by using one channel only. In this experiment, PC1 sends a flow of 10-Mbps UDP traffic with 1500-byte packets during 30 seconds by iperf to PC2. Figure 2 (b) shows the time series throughput behavior of two WBNs. From the figure, we can say that the OpenFlow based WBN can achieve the almost same performance with the static route based WBN. Thus, there is no performance degradation due to OpenFlow operation. Also, we conduct this experiment five times and obtain the average throughput of Mbps. Thus, we treat it as the maximum throughput of 3-hop WBN with a single channel. 102

6 In the next experiments, the OpenFlow based WBN is examined with 1, 2, and 3 available channels, respectively. In each experiment, PC1 sends a flow of 1-Mbps UDP traffic with 1500-byte packets by iperf to PC2 and increases the number of flows by one per 10 seconds. From the previous experiment, in such case, we can guess that the number of flow without packet losses is limited to 8 for each channel (16 flows for 2 channels and 24 flows for 3 channels). Figure 3 shows the throughput in time series. We can see from the figure that the throughput linearly increases up to 24 Mbps in response to the increase of channels. Therefore, we can remark that our framework can increase the network capacity while effectively utilizing three channels. Fig. 3. Time series throughput with increased 1 Mbps UDP flow 4 Conclusion In this paper, we propose a traffic management framework for wireless backbone network (WBN). First, we design a virtual AP that potentially has the unlimited number of channels, thereby enabling the utilization of all vacant channels. We then design an OpenFlow based WBN, which is the first trial applying OpwnFlow technology to WBN as far as we know. Finally, we present a traffic management framework that can utilize multiple channels for WBN simultaneously. The experimental results show that our WBN can increase the network capacity with maximum utilization of multiple channels. Acknowledgments This work was partly supported by Strategic Information and Communications R&D Promotion Programme (SCOPE) (project number: ) of Ministry of Internal affairs and Communications (MIC), Japan. 103