Literature Synthesis on Wireless Networks Management. Veenesh Jeena (JNXVEE001) CSC4000W 2010

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1 Literature Synthesis on Wireless Networks Management Veenesh Jeena (JNXVEE001) CSC4000W 2010 Abstract In this paper, we look a Wireless Mesh Networks (WMN). We discuss the importance of WMN s and some of the applications that they have, that traditional wired networks cannot achieve as easily and effortlessly. Managing WMN s however, are not as easily done as wired networks, due to the dynamic nature of the nodes. As a result, traditional network management methods, like Simple Network Management Protocol (SNMP) cannot be implemented and still be expected to work as efficiently as they do for wired networks. Because of this, new management tools have to be developed, to cope with the differences in wired and wireless environments. This paper has a look at two such tools, MeshMan and ReMesh, as solutions to management problems, and we see that they do address the problems of SNMP. 1. Introduction Wireless mesh networks (WMN) consist of routers and clients. The routers are devices that have minimal mobility, and provide the routing of data within the network. Clients are devices that connect to the network like cell phones, laptops or other wireless devices. A particular wireless mesh network may or may not be connected to the internet. [6] A characteristic of WMN are that they are multi-hop networks. That is, packets are routed from one router to another until the destination is reached. This allows WMN to operate over great distances by forming a path in a chain-like manner. WMN s are also redundant, so when one node fails, then rest of the nodes can still operate. Another characteristic of WMN is that they can add devices to the network without changing the physical layout of the network (since no cables need to be laid etc.). Adding nodes to the network also increases the reach of the network. Wireless networks are also decentralized, meaning that there is no single server used to manage the transmission of data. Each node is responsible for its own routing. This makes the network more flexible, and can allow routing to continue even when a router is removed from the network. WMN s are also self-forming, meaning that the mesh network forms itself, once the nodes have been configured and activated.

2 Below is an example of a WMN, displaying the above properties of a WMN. Figure 1: A wireless mesh network [15] A reason why WMN are such an attractive technology, especially in developing countries like countries in Africa, is that they are relatively cheap and can thus drive down the price of communication access. Also, WMN s can quickly form ad-hoc networks that are particularly useful in disaster relief situations when normal communication is not possible. [4] WMN do have their drawbacks. Managing WMN s can be a difficult task due the flexibility of the network. The network has the potential to change and grow all the time, thus, needing complex routing algorithms and methods for discovering new or failed nodes. Roaming also becomes an issue. When a user moves too far from a router, they may experience performance degradation, or they may even degrade the performance of users when they connect to another router, increasing its load. The service levels of a router can also be affect by the environment or distance from other routers. These drawbacks of WMN s are not easy to monitor since routers can be placed far apart from each other. Hence, as wireless networks become more ubiquitous, it is important to provide a solution to manage WMN s, which can be utilized to easily operate and troubleshoot networks. [1]

3 2. Wireless Network Management Wireless ad hoc networks are characterized by strong dynamicity, heterogeneity of devices, bandwidth and energy constraints. This makes fixed network management architectures unsuitable. WMN s require new management mechanisms adapted to their functioning. The management tool of such networks must support the following characteristics: [2] Self-organized Ad-Hoc networks require a management scheme capable of adapting to nodes heterogeneity and movement. Robust Management should be maintained in a dynamic environment. Low Cost Ad-Hoc networks are limited in resources, so the impact of management traffic should be limited. Users expect the quality of service (QoS) from mobile ad hoc networks to be the close to that of wired networks. [2] However, it can be a difficult task providing and managing QoS in an ad-hoc network environment [8] due to the dynamics and mobility of the nodes. There are different Network Management Models (NMM) that one can use, each with their respective strengths and weaknesses, each model created to cover a different aspect of an ad-hoc network. In general, a NMM should monitor the health and status of the nodes and provide warnings for any abnormalities in the network. [11] The most widely used NMM over the internet, is the Simple Management Network Protocol (SNMP). [17] The SNMP emerged out of the International Standards Organization s (ISO) Network Model, which addresses the following 5 aspects as the major functional areas of a NMM: [7] Fault Management Accounting Management Configuration Management Performance Management Security Management Despite SNMP being widely adopted in the internet and wired networks, it is not a viable solution for network management in wireless ad hoc networks. Problems with SNMP over wireless networks are that, firstly, SNMP is designed to work over a heterogeneous link layer where network bandwidth and storage space are abundant. [17, 1]. However, according to [1], since routers in a WMN have limited memory storage, SNMP is heavy on bandwidth consumption and as a result, SNMP cannot address nodes more than one hop away. Also, SNMP cannot retrieve certain statistics in a WMN; [5] reports that

4 SNMP cannot retrieve information like hop count or current gateway used because of the characteristic of a WMN. Bandwidth monitoring is also limited to only being able to monitor the currently used bandwidth. This is not enough to determine, if in a WMN, the reason for low bandwidth between two nodes is poor communication or low traffic. [5] In the next section we look at tools that have been developed to overcome the shortages of SNMP. 3. Alternative Wireless Network Management Tools There are various tools that were developed to overcome the shortcomings of SNMP. Here we will look at two of these tools, MeshMan [1] and the ReMesh project [5], each of whom works very differently from the other MeshMan MeshMan operates at the network layer, providing a low-overhead solution to network management and cope with the dynamics of a wireless network at the network level. [1] MeshMan uses OpenWRT Linux Distribution on the nodes, designed to be deployed on wireless embedded devices. MeshMan is specifically designed to overcome the following constraints of SNMP: [1] Robustness of network failure To diagnose and correct network layer faults, the solution should be independent of the network layer Self-reconfiguration Failure and addition of nodes should easily be handled. MeshMan makes use of 3 components, common to NMM s, to achieve its goals: [1] Managing Entity An application that runs at a management station that controls the collection, analysis and processing of network management information. Managed Device and Agent The component being managed by the managing entity. It is implemented as a daemon running in the background, collecting information and transferring it back to the managing entity. Network Management Protocol This defines the communication protocol used between the managing entity and managed device.

5 3.2. The ReMesh Project ReMesh is a set of tools, instead of a single tool, that when used together provides a NMM. ReMesh hardware runs on the OpenWRT operating system as well, configured for the ReMesh project. According to the ReMesh Project, in order to monitor the network, the network monitoring tool must address the following issues: [5] Resource Constrained Devices Exclusive use of wireless communication Fluctuating link qualities Unfriendly node placement To address these above problems, the ReMesh project has developed tools aimed at satisfying the following: [5] Low user interaction Tools should reduce and simplify user interaction. Reliability Changing parameters should not hamper node communications Low disk footprint Software on each device should be kept to a minimum Low runtime footprint The node s priority is to route data in the network, management tools should not be depleting a nodes memory with management queries. Failure resilience Tools should be able to deal with nodes that suffer from communication failures The MeshMan and ReMesh Solutions Resource Constraints MeshMan uses a hierarchical addressing scheme to overcome memory constraints in the network. The addressing scheme is aimed at reducing management memory overhead. It works as follows: Each node is automatically assigned a variable length mesh ID, in a hierarchical fashion using dot decimal representation. (e.g. a mesh ID of means 3 is a child of 2, and 2 is a child of 1). These ID s are stored in the mesh manager, MeshMan s managing entity, at a central location. These ID s then serve as routing directives for the queries generated by the mesh manager for the routers. The mesh ID representation is more compact and incurs less memory overhead, as compared to a routing scheme that concatenates 48-bit MAC addresses to nodes along a path. [1] ReMesh uses the Optimal Link State Routing (OLSR) protocol to reduce memory usage on the nodes. The OpenWRT implementation of SNMP uses about 10% of node memory,

6 whereas OLSR uses only about 4.9%. Other ways in which memory is conserved, is that only the most fundamental libraries needed in the OpenWRT system is installed, achieving a low disk footprint. [5] This is however, the only way ReMesh saves on memory usage on the nodes Network Performance and Bandwidth Monitoring MeshMan uses tcpdump at the mesh manager to collect information on network activity and the tcptrace tool to estimate the bandwidth consumption by management tools. [1] MeshMan does not seem to have a mechanism for monitoring the network performance or total network traffic or even traffic at a particular node; it only monitors management traffic. ReMesh uses two tools for network performance monitoring: the Multi Router Traffic Grapher (MRTG) and Ntop. MRTG is a tool to monitor the traffic on network links. It generates HTML pages, containing images which represent traffic on a link. Ntop is a Web-based traffic measurement and monitoring application. Ntop focuses on traffic measurement and monitoring as well as information for network optimization and planning. [5] ReMesh also implements a system made up of three protocols: A shell script to obtain statistics, a database to store collected data and a web page to display information. The script is executed in the routers, and the data is sent at certain intervals to be stored in the database. The web page can then display this information in the form of graphs. [5]

7 Figure 2: Example of graphs generated by the ReMesh tools [5] Self-Reconfiguration and Fault Management MeshMan uses an adoption daemon to help with network fault management and find optimal routing paths. The adoption process works as follows: A child node periodically broadcasts a Discovery packet, with its path cost to the mesh manager. The node receives packets from neighbouring parents advertising their path costs. The child evaluates the lowest cost path, and then is adopted by the new parent. The parent then sends a DeleteRoute notification to the manager, to inform it of route changes. To cope with node failures, the DeleteRoute message is again used to inform the manager of the lost link. [1] ReMesh has not yet implemented a fully working autonomous network configuration scheme. Each node has to be individually configured before they are deployed in the network. The only tool that ReMesh does use to help with network management is Broadcast shell (BShell). BShell is a tool that can automate the process of addressing all nodes, and running desired commands on each node. This helps with failure resistance by keeping a log of errors that could occur in executing commands on a node, and keep the remaining nodes functioning. [5]

8 4. Conclusion We have seen reasons why SNMP cannot be an effective NMM, particularly because SNMP: Needs a lot of resources (esp. for node memory) Cannot reach nodes more than 1 hop away Cannot retrieve all network statistics (hop count, current gateway used) Cannot do detailed bandwidth monitoring As a response to these problems, we have seen two solutions, MeshMan and ReMesh, which provide a comparatively better solution to SNMP on aspects of network management. However these two are not the only solutions for network management, other tools have been researched as well like: Ad hoc network management protocol (ANMP) [17] Common Management Information Protocol (CMIP) [17] Researched management tools aren t the only tools that that exist; commercial products already exist such as CISCO [3], MERAKI [10] and Open-Mesh [12]. These can be expensive to purchase, or even maintain. They do provide network management through the web browser, using a tool called a dashboard, which provides a geographical layout and visual information on the network. Further research on these management tools could also extend to involve mobile phones as a manager. With the processing power of mobile phones ever-increasing, management software could be ported to mobile phones. This would allow management on-the-move and even go on-site to the nodes to monitor them in real time.

9 References [1] Aseeja, V. and Zheng, R MeshMan: A management framework for wireless mesh networks. In Proceedings of the 11 th IFIP/IEEE international Conference on Symposium on Integrated Network Management (New York, NY, USA, June 01 05, 2009), IEEE Press, Piscataway, NJ, , DOI: /INM ( [2] Badonnel, R., State, R., and Festor, O Management of mobile ad hoc networks: information model and probe-based architecture. Int. J. Netw. Manag. 15, 5 (Sep. 2005), DOI= [3] CISCO available at: Accessed 26 April 2010 [4] Dhorat I. Afrimesh, Simple & Easy setup of wireless mesh networks for rural Africa Available from: (2009) Accessed 15 April 2010 [5] Duarte, J.L. and Passos, D. and Valle, R.L. and Oliveira, E. and Muchaluat-Saade, D. and Albuquerque, C.V., Management Issues on Wireless Mesh Networks, Latin American Network Operations and Management Symposium, September 2007, Pages 8-19, DOI: /LANOMS ( [6] Ian F. Akyildiz, Xudong Wang, Weilin Wang, Wireless mesh networks: a survey, Computer Networks, Volume 47, Issue 4, 15 March 2005, Pages , ISSN , DOI: /j.comnet ( 2/2/9fa1587e47665f1fb3f7fb461461dd6b) [7] International Standard, Information processing systems Open Systems Interconnection Basic Reference Model, Part 4: Management framework. Reference Number: ISO/IEC : 1989 (E) Available at: [8] Kaustubh S. Phanse, Luiz A. DaSilva, Addressing the requirements of QoS management for wireless ad hoc networks*, Computer Communications, Volume 26, Issue 12, 21 July 2003, Pages , ISSN , DOI: /S (02)00261-X. (

10 [9] Lei Zhang, Jogesh K. Muppala, Samuel T. Chanson, Integrated location management and location-aided routing system for mobile ad hoc networks, Journal of Parallel and Distributed Computing, Volume 66, Issue 3, March 2006, Pages , ISSN , DOI: /j.jpdc ( [10] Meraki available at: Accessed 27 April 2010 [11] Network Management Systems Available at: Accessed 29 April 2010 [12] Open-Mesh available at: Accessed 27 April 2010 [13] Rowe, D The mesh potato. Linux J. 2009, 188 (Dec. 2009), 5. Available at: y2= &coll=acm&dl=acm&cfid= &cftoken= Accessed 15 April 2010 [14] Simple Network Management Protocol Available at: Accessed 29 April 2010 [15] Senior Projects 2009 Available at: Accessed 27 April 2010 [16] Valle R. De T., Passos D., Albuquerque, C., Saade, D.C.M. Mesh Topology Viewer (MTV): an SVG-Based Interactive Mesh Network Topology Visualization Tool. In IEEE Symposium on Computers and Communications (July, 2008), , DOI: /ISCC ( [17] Wenli Chen, Nitin Jain, Singh,S., ANMP: Ad hoc network management protocol. IEEE Journal on Selected Areas in Communications, Volume 17, Issue 8, August 1999, Pages , ISSN , DOI: /