WIRELESS MESH NETWORKS

CHAPTER 12: WIRELESS MESH NETWORKS I F Akyildiz Broadband & Wireless Networking Laboratory School of Electrical and Computer Engineering Georgia Institute of Technology Tel: 404-894-5141; Fax: 404-894-7883 Email: ian@ece.gatech.edu Web: http://www.ece.gatech.edu/research/labs/bwn Wireless Mesh Networks I.F Akyildiz, et.al., “Wireless Mesh Networks; A Survey”, Computer Networks Journal, March 2005  The term 'wireless mesh networks' describes wireless networks in which each node can communicate directly with one or more peer nodes  The term 'mesh' originally used to suggest that all nodes were connected to all other nodes, but most modern meshes connect only a sub-set of nodes to each other  Still, this is quite different than traditional wireless networks, which require centralized access points to mediate the wireless connection  Even two 802.11b nodes that are side-by-side in infrastructure mode must send data to each other through the access point IFA’05 ECE6610 Wireless Mesh Networks  Nodes are comprised of mesh routers and mesh clients  Each node operates not only as a host but also as a router, forwarding packets on behalf of other nodes that may not be within direct wireless transmission range of their destinations  A WMN is dynamically self-organized and self-configured, with the nodes in the network automatically establishing and maintaining mesh connectivity among themselves IFA’05 ECE6610 Wireless Mesh Networks  Extend the range and link robustness of existing Wi-Fi’s by allowing mesh-style multi-hopping  A user finds a nearby user and hops through it - or possibly multiple users - to get to the destination  Every user becomes a relay point or router for network traffic  Mesh networks consist of multiple wireless devices equipped with COTS802.11 a/b/g cards that work in ad-hoc fashion  802.11 capable antennas placed on rooftops allow a large area coverage IFA’05 ECE6610 Network Architecture  WMNs consist of two types of nodes: Mesh Routers and Mesh Clients  A wireless mesh router contains additional routing functions to support mesh networking  It is equipped with multiple wireless interfaces built on either the same or different wireless access technologies  A wireless mesh router can achieve the same coverage as a conventional router but with much lower transmission power through multi-hop communications IFA’05 ECE6610 WMN COMPONENTS Examples of mesh routers based on different embedded systems: (a) PowerPC and (b) Advanced Risc Machines (ARM) IFA’05 ECE6610 WMN COMPONENTS Examples of mesh clients: (a) Laptop, (b) PDA, IFA’05 (c) Wi-Fi IP Phone and (d) Wi-Fi RFID Reader ECE6610 WMN COMPONENTS IFA’05 ECE6610 WMN COMPONENTS IFA’05 ECE6610 Wireless Mesh Networks  Conventional nodes (e.g., desktops, laptops, PDAs, PocketPCs, phones, etc.) equipped with wireless network interface cards (NICs) can connect directly to wireless mesh routers  Customers without wireless NICs can access WMNs by connecting to wireless mesh routers through, e.g., Ethernet  Thus, WMNs will greatly help users be always-on-line anywhere anytime IFA’05 ECE6610 10 Standard Activities To enhance the 802.16 mesh, several proposals have been submitted to the standard committee A group within 802.16, the Mesh Ad Hoc committee, is investigating ways to improve the performance of mesh networking It is understood that only a small amount of meshing is required to see a large improvement in the coverage of a single base station More importantly, the following issues are considered in specifying the 802.16 mesh MAC protocol: * avoiding hidden terminal collisions, * selection of links, * synchronization, * power versus data rate tradeoffs, and * greater routing-MAC interdependence IFA’05 ECE6610 14 ADVANTAGES OF WMNs  Price: 802.11 radios have become quite cheap, but the radios are often still among the most expensive elements of such a network The fact that each mesh node runs both as a client and as a repeater potentially means saving on the number of radios needed and thus the total budget  Ease and simplicity: If you have a box that is pre-installed with wireless mesh software and uses standard wireless protocols such as 802.11b/g, the setup is extremely simple Since routes are configured dynamically, it is often enough to simply drop the box into the network, and attach whatever antennas are required for it to reach one or more existing neighboring nodes (assuming that we can solve the issue of IP address allocation)  Organization and business models: The decentralized nature of mesh networks lends itself well to a decentralized ownership model wherein each participant in the network owns and maintains their own hardware, which can greatly simplify the financial and community aspects of the system IFA’05 ECE6610 14 ADVANTAGES OF WMNs  Network robustness: The character of mesh topology and ad-hoc routing promises greater stability in the face of changing conditions or failure at single nodes, which will quite likely be under rough and experimental conditions  Power: The substrate nodes of a mesh network can be built with extremely low power requirements, meaning that they can be deployed as completely autonomous units with solar, wind, or hydro power Power generating units are typically connected to points of infrastructure and human presence This makes them valid locations for network nodes As a secondary benefit, the presence of integrated network nodes within power networks may allow for better monitoring and management IFA’05 ECE6610 14 ADVANTAGES OF WMNs  Integration: Mesh hardware is typically small, noiseless, and easily encapsulated in weatherproof boxes This means it also integrates nicely outdoors as well as in human housing  Reality fit: Reality rarely comes as a star, ring, or a straight line In difficult terrain be that urban or remote where not every user can see one or few central points, chances are one can see one or more neighboring users IFA’05 ECE6610 14 FURTHER ADVANTAGES  Provides a value-added entry into the high-speed wireless packet and data business  Utilizes 802.11 technology—the interface of choice for high-speed wireless packet data  Offers high-speed wireless packet data access across a wider coverage area  Today's cellular systems not provide the bandwidth available in WLANs  Today's isolated hotspot 802.11 deployments not satisfy user desire for ubiquitous access or for mobility  Emergence of small-form factor terminals with 802.11 wireless interfaces means impending demand for adding mobility to WLAN packet data services  Minimizes cost of capital, installation and commissioning  Utilizes low-cost 802.11 technology  Uses wireless links for backhaul to eliminate costs associates with installation of wired interconnect IFA’05 ECE6610 14 FURTHER ADVANTAGES  Auto-configuration algorithms in Wireless Access Point eliminate costs associated with engineering and organization of the wireless backhaul network  Minimizes cost of operations  Uses wireless links for backhaul to eliminate costs associated with ongoing leasing of facilities  Auto-configuration, self-organizing and self-healing are intrinsic to the Wireless Mesh Network solution  Centralized OAM&P minimizes staffing requirements  Highly flexible in terms of capacity, coverage and availability  Increasing capacity, coverage and/or availability simply means deploying more Wireless Access Points  Wireless Access Points maybe deployed indoors or outdoors  IFA’05 ECE6610 15 Ugly Truths Radio is a shared medium and forces everyone to stay silent while one person holds the stage Wired networks, on the other hand, can and hold multiple simultaneous conversations In a single radio ad hoc mesh network, the best you can is (1/2)^^n at each hop So in a multi hop mesh network, the max available bandwidth available to you degrades at the rate of 1/2, 1/4, 1/8 By the time you are hops away the max you can get is 1/16 of the total available bandwidth IFA’05 ECE6610 15 Ugly Truths That does not sound too bad when you are putting together a wireless sensor network with limited bandwidth and latency considerations It is DISASTROUS if you wish to provide the level of latency/throughput people are accustomed to with their wired networks Consider the case of just 10 client stations at each node of a hop mesh network The clients at the last rung will receive -at best- 1/(16,0000) of the total bandwidth at the root IFA’05 ECE6610 15 Ugly Truths Why has this not been noticed as yet? Because first there are not a lot of mesh networks around and second, they have not been tested under high usage situations Browsing and email not count Try video - where both latency and bandwidth matter - or VOIP where the bandwidth is a measly 64Kbps but where latency matters Even in a simple hop ad hoc mesh network with 10 clients, VOIP phones will not work well beyond the first or second hop – the latency and jitter caused by CSMA/CA contention windows (how wireless systems avoid collisions) will be unbearable Mesh networks are a great concept But the challenge lies in managing the dynamics of mesh networks so users receive an acceptable level of performance in terms of both latency and throughput It is time to focus on solving some real problems to make mesh networks scale and provide stable performance IFA’05 ECE6610 15 Is this a Disruptive Technology?  In its vision of WLANs and wireless access networks of the very near future, Mesh Networks sees every client device also becoming a relay point or router for network traffic  One immediate benefit is that such networks can in effect see around corners  Even line-of-sight network technologies like 802.11 can become non-line-of-sight - almost overnight if Mesh Networks can deliver what it is promising  And the next-generation networks the company is building will also power mobile broadband services IFA’05 ECE6610 15 What is a Disruptive Technology?  "In real-world terms, it has to meet at least two of three criteria: Be ten times cheaper than any alternative, have ten times higher performance, and ten times higher functionality All three is best."  There are two parts to Mesh Networks' supposedly disruptive technology IFA’05 ECE6610 15 WMNs as Disruptive Technology  One is QDMA (quad-division multiple access), a proprietary radio technology developed for and currently used by WMNs  QDMA's most notable characteristics are that it is IP from end to end and supports high-speed mobile broadband access and infrastructure-free "ad hoc peer-to-peer networking."  The company claims it can deliver up to Mbps to each user in a QDMA wireless network  The technology also has built-in GPS capabilities and QoS (quality of service) for IP voice and video IFA’05 ECE6610 15 REMARKS  For QoS in the strict sense, there are doubts  But for Video and Data with a certain bandwidth, they will take off in wireless as the physical wireless capacity becomes really broadband and reliable for mobile end users  Because, currently, GSM/GPRS systems are widely used here for data and multimedia (to a certain degree, such as small video, image and sound captures with the camera of the cellular phone) communication, although its data rate is very low GPRS data rates were around 14.4-20 IFA’05 ECE6610 15 REMARKS  However, the interest of the people and the success in the implementation draws big companies' attention  Especially the future application of Mesh networks is considered to realize Mobile WiFi by integrating Mesh Enabled Architecture (MEA) architecture with 802.11 access points  MEA consists of wireless cards, cheap mesh wireless routers, portable wireless routers, and intelligent access points IFA’05 ECE6610 15 Wireless Mesh Networks Case Studies Medford, OR (70,000 people) 24 square miles – broadband communications ROI – months possible $770,000 to install Garland, TX (221,000 people) 57 square miles – broadband communications Cost Avoidance – subscription fees / cell towers IFA’05 ECE6610 [...].. .Wireless Mesh Networks  Moreover, the gateway/bridge functionalities in mesh routers enable the integration of WMNs with various existing wireless networks such as cellular, wireless sensor, wireless- fidelity (Wi-Fi), worldwide interoperability for microwave access (WiMAX) networks  Consequently, through an integrated WMN, users of existing networks are provided with otherwise... a wired backbone  Compared to wired networks, e.g., cable or optical networks, wireless mesh MAN is an economic alternative to broadband networking, especially in underdeveloped regions  Wireless mesh MAN covers a potentially much larger area than home, enterprise, building, or community networks  Thus, the requirement on the network scalability by wireless mesh MAN is much higher than that by other... impossible services of these networks IFA’05 ECE6610 11 Network Architecture Classification 1 INFRASTRUCTURE MESHING 2 CLIENT MESH NETWORKING 3 HYBRID MESH NETWORKING IFA’05 ECE6610 12 INFRASTRUCTURE MESHING  This includes mesh routers that form an infrastructure for clients that connect to them  This can be built using various types of radio technologies  The mesh routers form a mesh of self-configuring,... radio technologies as mesh routers, they can directly communicate with mesh routers IFA’05 ECE6610 14 INFRASTRUCTURE MESHING IFA’05 ECE6610 15 INFRASTRUCTURE MESHING  If different radio technologies are used, clients must communicate with the base stations that have Ethernet connections to mesh routers  These are the most commonly used  For example, community and neighborhood networks can be built... increased when compared to infrastructure meshing; the end-users have to perform additional functions such as routing and self-configuration IFA’05 ECE6610 17 Client WMNs IFA’05 ECE6610 18 HYBRID WMNs  This architecture is the combination of infrastructure and client meshing  Mesh clients can access the network through mesh routers as well as directly meshing with other mesh clients  While the infrastructure... Self-Healing, and Self-Organization  Mobility Dependence on the Type of Mesh Nodes  Multiple Types of Network Access  Dependence of Power-Consumption Constraints on the Type of Mesh Nodes  Compatibility and Interoperability with Existing Wireless Networks IFA’05 ECE6610 21 WMNs vs AD HOC Networks Dedicated Routing and Configuration:  In ad-hoc networks, end-user devices also perform routing and configuration... IFA’05 ECE6610 24 WMNs vs AD HOC Networks Compatibility:  WMNs contain many differences when compared to ad hoc networks  Ad hoc networks can be considered as a subset of WMNs  More specifically, the existing techniques developed for ad-hoc networks are already applicable to WMNs  As an example, through the use of mesh routers and routingcapable end-users, multiple ad hoc networks can be supported in... themselves  With gateway functionality, mesh routers can be connected to the Internet IFA’05 ECE6610 13 INFRASTRUCTURE MESHING  It provides backbone for conventional clients and enables integration of WMNs with existing wireless networks, through gateway/bridge functionalities in mesh routers  Conventional clients with Ethernet interface can be connected to mesh routers via Ethernet links  For conventional... including directional antennas IFA’05 ECE6610 16 Client WMNs  Client meshing provides peer-to-peer networks among client devices  Client nodes constitute the actual network to perform routing and configuration functionalities as well as providing end-user applications to customers  A mesh router is not required for these types of networks  A packet destined to a node in the network hops through multiple... in the same channel in ad-hoc networks constraining the performance IFA’05 ECE6610 23 WMNs vs AD HOC Networks Mobility:  Since ad-hoc networks provide routing using the end-user devices, the network topology and connectivity depends on the movement of users  This imposes additional challenges to routing protocols as well as network configuration and deployment  Since mesh routers provide the infrastructure ... However, these solutions only achieve a low end-to-end throughput, because they cannot significantly reduce the probability of contentions among neighboring nodes As long as contention occurs frequently,... using long-range communication techniques including directional antennas IFA’05 ECE6610 16 Client WMNs  Client meshing provides peer-to-peer networks among client devices  Client nodes constitute... Configuration:  In ad-hoc networks, end-user devices also perform routing and configuration functionalities for all other nodes  However, WMNs contain mesh routers for these functionalities