Design and Implementation of Wireless Mesh Network Testbed SJTU-MESH Yue Wu, Donglai Sun, Ping Yi Junhua Tang School of Information Security Engineering Shanghai Jiao Tong University Shanghai 200240, China (
[email protected],
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[email protected]) Abstract—The emerging Wireless Mesh Networks (WMN) is a broadband access technology with the properties of multi-hop and self-organization, which has advantages of easy deployment, self-recovering, low cost and high scalability. The paper firstly introduces related works of wireless mesh networks; then describes the deployment of a real indoor testbed SJTU-MESH architecture and click based implementation including hardware platform, software platform and system integration;; and then presents real testbed performance evaluation and analysis, finally it gives conclusions and future remarks.
Keywords- wireless mesh network, testbed, design and implementation, performance evaluation
I.
INTRODUCTION
The emerging Wireless Mesh Network (WMN) combines the characteristics of self-organization and multi-hop communication[1]. It has many advantages such as easy deployment, self-recovering, low cost and high scalability, which is a promising network technology for broadband wireless network access, government facilities, disaster salvation and industry management, etc. It is also considered as an indispensable technology for the wireless city project which receives enormous attention nowadays. Mobile laptop users can easily use the multi-hop data link provided by the mesh routers to access the Internet, while the wired infrastructure and complex management is no longer necessary and the wireless access becomes more convenient. WLAN-based mesh network inherits the desirable attributes such as low-cost and wide-deployment from WLAN, while acquired the advantages of mesh as large coverage, scalability and robustness.[2]. The 802.11 working group in IEEE 802.11 TGs defines an extended service set (ESS) mesh networking[3][4]. Our wireless mesh network testbed, called Shanghai Jiaotong University Mesh Network (SJTU-MESH) is a Click modular router[5] based WLAN mesh network composed entirely of distributed physical nodes, the hardware platform of which is based on AsusWL500W supporting IEEE 802.11b/g/n standards. The 8 nodes are distributed in 8 rooms respectively with two gateways connecting with Internet infrastructure. The AsusWL500W wireless routers have been upgraded with the OpenWRT2[6] Linux distribution so that
they can run in ad hoc mode. All nodes have an ad hoc routing protocol installed that establishes and maintains paths between nodes. Currently, Source Reactive Routing SrcRR[7] is chosen as the core routing protocol of SJTU-MESH testbed and implemented based on click modular router software, and finally various kinds of performance parameters are evaluated upon SJTU-MESH testbed. The main contribution of this paper is twofold: i) reporting on the deployment of a real indoor testbed SJTU-MESH utilizing click based router embedded technology and ii) evaluating various kinds of performance parameters in real testbed deployment and getting nearly the same performance of meraki[8] which is a famous business brand for WLAN mesh networking. The paper is organized as follows: Section 2 introduces related works of WLAN based mesh networks; Section 3 describes SJTU-MESH testbed architecture and click based implementation including hardware platform, software platform and system integration; Section 4 presents real testbed performance evaluation and analysis. Section 5 gives conclusions and future remarks. II.
RELATED WORKS
Roofnet [9] is an experimental 802.11b/g mesh network built by MIT. Each node in Roofnet has an antenna installed on the roof of a building. Aguayo et al. [10] analyzed the link layer behavior on the Roofnet testbed and described the impact of distance, SNR and transmission rate on the packet loss. While Roofnet’s hardware is composed of PC computer with pre-installed software, 802.11b card, antenna with chimney mount and 50 to 150 feet of low-loss LMR400 cable, it is for experiment and not suitable for real deployment. Microsoft Mesh Connectivity Layer [11] is a Microsoft Research open source WMN implementation. MCL fits between the network and link layers, providing an abstraction level to its surrounding layers and minimizing the changes required to make them work with it. The existence of this 2.5 interlayer protocol is transparent to protocols running on top of it (e.g., TCP/IP), as well as those running beneath it (e.g., MAC layer). There is hence no need to change these technologies in order to work with MCL. UCLA Network Research Lab has created a testbed for Wireless Mesh Networks using the MCL and evaluated the performance of real-time traffic in a WMN[12].But the MCL is based on windows operating system
This work was supported in part by National Science Foundation Key Project under Grants No 60932003 and National High-tech Research 863 Program of China under Grants No 2006AA01Z436 and No.2007AA01Z452.
978-1-4244-5143-2/10/$26.00 ©2010 IEEE
which cannot be further developed by other institutions and universities. The University of California, Santa Barbara Mesh Testbed [13] is an experimental wireless mesh network deployed on the campus of UC Santa Barbara. The network consists of 25 nodes equipped with multiple IEEE 802.11a/b/g wireless radios and distributed on five floors of the Engineering 1 building. The focus is that of designing protocols and systems for the robust operation of multi-hop wireless networks. The Broadband and Wireless Network (BWN) Lab at Georgia Institute of Technology [14] has built a WMN testbed. This WMN, called BWN-Mesh, consists of 15 IEEE 802.11b/g based mesh routers, with several among them connected to the Internet. The routers are located in various rooms on the floor where the BWN Lab resides. By changing the topology of the network, experiments investigating the effects of interrouter distance, backhaul placement, and clustering were performed along with mobility experiments using laptops in the testbed. Currently, the research is focused on adaptive protocols for transport layer, routing and MAC layers, and their cross-layer design. The 802.11 working group in IEEE 802.11 TGs[3] defines an extended service set (ESS) mesh (referred to here as a mesh network) as a collection of WLAN devices interconnected with wireless links that enable automatic topology learning and dynamic path configuration. 802.11 mesh networks will be based on extensions to the IEEE 802.11 MAC standard, based on the definition of a mesh network architecture and new protocol mechanisms. Hybrid Wireless Mesh Protocol (HWMP) is the default routing protocol of IEEE 802.11s. The LIP6 laboratory of Universit´e Pierre et Marie Curie has deployed wireless mesh network testbed, called MeshDVNet [15]. This work has mainly concerned with an efficient cross-layer routing to increase as much as possible the transport capacity of the mesh backbone and a mechanism able to effectively manage users’ mobility. MeshDV is a unique framework that leverages on the two-tier architecture of WMNs. Most of the aforementioned testbeds are either small scale non-embedded platform for demonstration or just for academic research, while our SJTU-MESH testbed is not only for research purpose but also for real application deployment for Shanghai Telecom Information Life Experiencing Hall and Maritime Bureau Office Building of Shanghai Yangshan Deep Water Harbor, upon which various kinds of performance parameters are evaluated. III.
SJTU-MESH TESTBED ARCHITECTURE AND CLICK BASED IMPLEMENTATION
A. Hardware Platform Design The hardware platform is based on AsusWL500W which is a wireless router supporting IEEE 802.11b/g/n standards. It consists of three modules: core processing module, wired network communication module and wireless network communication module. Each module is interconnected by interfaces on the board.
The core processing module includes Broadcom 4704@266MHz CPU, 8MB Flash, 32MB RAM and Power Module; while the wired communication module includes 4 LAN and 1 WAN 10/100M ethernet network interfaces and serial interface module; and the wireless communication module consists of wireless minipci interface and wireless network card. In order for the convenience of driver development, the original Broadcom 4321 wireless network card is replaced by Artheros Ar5414 card on our platform. B. Software Platform Design Click is a new software architecture for building extensible and configurable routers. A Click router is assembled from packet processing modules called elements. Individual elements implement simple router functions like packet classification, queuing, scheduling, and interfacing with network devices. A router configuration is a directed graph with elements at the vertices; packets flow along the edges of the graph. Configurations are written in a declarative language that supports user-defined abstractions. This language is both readable by humans and easily manipulated by tools. Due to Click's architecture and language, Click router configurations are modular and easy to extend. Each extension simply adds a couple elements to the base IP configuration. Other configurations, such as Ethernet switches, firewalls, and traffic generators, reuse many of the IP router's elements. Click software runs in the Linux kernel; on conventional PC hardware. Source reactive routing SrcRR[7] is chosen as the core routing protocol of SJTU-MESH testbed and implemented based on click modular router software, which has five functions that are shown in figure 1.
Figure 1.
Functional modules of SrcRR protocol
The leftmost module MetricFlood and subsequent procedures send broadcast packets containing metric value in order that the latest metric for a link can be calculated; The second functional module mainly deals with routing data such as Time-To-Live (TTL) parameter, and then classifies packets according to IP header to further processing; The third module implements simple route request and response, mainly focusing on processing probe packets for optimal route searching; The fourth functional module ETTstat is an important part in the whole routing protocol since it is responsible for link quality monitoring, the result of which can have a direct impact on link metric value. The last module GateWaySelect is concerned with choosing an optimal one from various gateways connecting to the Internet.
C. System Integration System architecture of Shanghai Jiaotong University Mesh Testbed (SJTU-MESH) is shown in figure 2. Above the AsusWL500W platform is the hardware driver, and then embedded linux based operating system OpenWRT is chosen to implement various functions of general wireless router such as network address translation (NAT), routing and switching etc.
Figure 2.
SJTU-MESH system architecture
Wireless mesh network module works upon OpenWRT to implement the following four functions, i.e., wireless link quality monitoring and decision, multihop data transmission over backbone network, automatic gateway selection and recovery, self-organizing and self-adaptive function. IV.
A. Throughput Figure 4 shows upload and download throughput performance versus hop counts. The throughput from one hop of local gateway node is at least 2Mbps. With the increasing of hop counts, throughput decreases nearly half of the previous one due to the wireless channel fading characteristics. There is still 450kbps or so data throughput at 3 hops which is about 250 meters away from gateway, while it is impossible for general wireless router to work at this distance.
Figure 4.
throughput performance
B. packet loss and delay
TESTBED EVALUATION AND ANALYSIS
The chain structure of testbed is deployed in order to get the network performance evaluation in multi-hop environment. The topology of testbed is shown in Figure 3. Two gateways which connect with Internet infrastructure are in room 1 and room 7 respectively, other wireless mesh routers are placed in each room.
Figure 5.
Figure 3.
packet loss performance
Topology of SJTU-MESH testbed
Three parameters are chosen to evaluate the testbed performance in multi-hop mesh network scenarios, which are throughput, packet loss and average delay. The performance of SJTU-MESH embedded router is also compared with the meraki wireless mesh network router[8].
Figure 6. average delay performance
Packet loss and delay are two important parameters to evaluate performance of real time data transmission. 32 bytes ping packet is used for testing without any retransmission
mechanisms. As shown in figure 5 and 6, average packet loss and delay both increase with hop counts. After 3 hops, the network performance deteriorates severely which can not be accepted in many application scenarios. C. Comparison and analysis Figure 7 illustrates throughput comparison between SJTUMESH and Meraki. The throughput performance of SJTUMESH at all distances is a bit lower than that of Meraki with antenna, while far better than that of Meraki without antenna.
Thr oughput ( kbps)
3000 2500
Mer aki ( Wi t h Ant enna) Mer aki ( Wi t hout Ant enna) SJTU- MESH
2000 1500 1000
V.
The paper describes the deployment of SJTU-MESH utilizing click based router embedded technology, and evaluates various kinds of performance parameters in real testbed deployment. By comparison it is concluded that all aspects of performance of SJTU-MESH get nearly the same as that of meraki for wireless mesh networking. Our future work will focus on evaluating the performance of real-time multimedia traffic upon testbed and designing security protocols for SJTU-MESH to enhance testbed functions. REFERENCES [1] [2]
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[3]
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Mul t i - hop Communi cat i on Range
Figure 7. throughput comparison between Meraki and SJTU-MESH
Figure 8 and figure 9 show the average delay and packet loss comparison between SJTU-MESH and Meraki. The performance of SJTU-MESH is between that of Meraki with antenna and Meraki without antenna, and it is concluded that all aspects of performance of SJTU-MESH are approaching those of Meraki with antenna provided that the omni-antenna is carefully designed.
[4] [5]
[6] [7]
[8] [9] [10]
[11] [12] Figure 8. average delay comparison between Meraki and SJTU-MESH [13] [14] [15]
Figure 9. average packet loss comparison between Meraki and SJTU-MESH
CONCLUSIONS AND FUTURE REMARKS
I.F.Akyildiz and X.Wang., A Survey on Wireless Mesh Networks, IEEE Radio Communications, Sep. 2005. pp. 23—30. S.M.Faccin et al., Mesh WLAN Networks: Concept and System Design, IEEE Wireless Communication, Vol. 13, Issue 2, April 2006. pp. 10— 17. IEEE 802.11s (mesh networking), Draft Amendment to Standard for information Technology - Telecommunications and Information Exchange Between Systems - Local and metropolitan area networks LAN/MAN Specific Requirements - Part II: Wireless Medium Access Control (MAC) and Physical Layer (PHY) specifications: Amendment: ESS Mesh Networking. IEEE Unapproved draft P802.11s/D2.02 (September 2008) Xudong Wang, Azman O. Lim, IEEE 802.11s wireless mesh networks: Framework and challenges，Ad Hoc Networks 6 (2008) 970–984 Eddie Kohler, Robert Morris, Benjie Chen, John Jannotti, M. Frans Kaashoek. The Click modular router. ACM Transactions on Computer Systems, 18(4), November 2000 OpenWrt Community. Available from: < http://www.openwrt.org> D. S. J. De Couto, D. Aguayo, J. Bicket, and R. Morris, A highthroughput path metric for multi-hop wireless routing, in Proceedings of ACM Mobicom, 2003. Meraki inc. Available from: < http://meraki.com/ >. “Mit roofnet project.” [Online]. Available: http://pdos.csail.mit.edu/roofnet/doku.php D. Aguayo, J. Bicket, S. Biswas, G. Judd, R. Morris, Link-level measurements from an 802.11b mesh network, in: ACM Annual Conference of the Special Interest Group on Data Communication (SIGCOMM), August 2004 Microsoft Mesh Networks. Available from: . Vincent Chavoutier, Daniela Maniezzo, Claudio E. Palazzi, Mario Gerla, Multimedia over Wireless Mesh Networks:Results from a Real Testbed Evaluation, The Sixth Annual Mediterranean Ad Hoc Networking WorkShop, pp. 56–62, Corfu, Greece, June 12–15, 2007 University of California Santa Barbara, UCSB MeshNet, http://moment.cs.ucsb.edu/meshnet/. BWN lab wireless mesh networks research project. Available from: . LIP6-UPMC RNRT Infradio Project. [Online]. Available: http://rnrtinfradio.lip6.fr/indexEnglish.html
