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MIMO will clean up the mesh in your network In any case, wired home networks will often utilise existing physical networks and therefore the physical topology is already set, as with power or telephone cabling. The story of mesh in the home is, therefore, almost entirely about wireless.

Extending the mesh with MIMO Wireless mesh technologies, however, evolved first for metro or local loop networking and are only now being considered for deployment in the home. Meanwhile, MIMO has given home networks a boost by exploiting the varying paths radio signals tend to take between points when there is no direct line of sight. MIMO tackles two problems. Firstly, it reduces the incidence of communication blackspots Mesh networks are evolving to where signals previously did not reach, support connectivity inside the home, and secondly, it improves Quality of Service (QoS) for real time applications such as with a number of CE companies video, by providing an alternative path looking at mesh WiFi as a way in the event of transmission interruptions. “MIMO leverages what has traditionally of improving the ability to provide been a liability for radio, which is the ubiquitous home coverage. Philip multiple paths with signals bouncing Hunter explores the potential role around,” says Frank Hanzlik, managing director of the WiFi Alliance, which formed that mesh can play in the connected a group in late 2006 looking at mesh networking capability and applications in the home. With appropriate signal ireless was too slow and to allow re- in the event of processing as in MIMO networks, unreliable for transmitting congestion, or failure of either nodes this multiple path effect can be Wvideo within the home or or links. In a full mesh, every device is exploited to provide redundancy anywhere else in the early days of WiFi, but connected to every other, so in a wired and network penetration. the maturation of mesh and MIMO (Multiple network, the amount of cable required But MIMO cannot guarantee to reach Input Multiple Output) technologies is increases geometrically with the number all corners of every home on its own. changing all that. By the time home net- of nodes - a three node network requires In some cases, the physical barriers works are widely deployed, WiFi is likely just three links, while a six node network to communication between any two points to be the most popular option for buildings requires 15 links. For this reason, wired are too great for signals to traverse via that do not already have a wired network networks with large numbers of nodes any path, as Dave Park, VP of product installed. The latest HomePlug AV standard, tend to be just partially meshed, with marketing at BelAir, a provider of mesh enabling transmission of data and video each device connected to a few others, networks for hotels, campuses and over the mains wiring, also avoids the sometimes only the immediate neighbours. metropolitan areas, points out. “The main need for additional cables, but only supports Within the home, meshing could be challenge in the home is the propagation portability between sockets, and not full deployed in principle across a wired network environment and mesh could help, for mobility as required by the growing number but there would be little point since it would example, reach into the basement,” of battery powered or rechargeable devices. not solve any bandwidth problems, which he says. In this case, a device - say located Mesh comes in various guises. It first are not really the issue here, while the small at the top of the house - might not be able evolved in trunk telephony networks risk of node or link failure can be tolerated. to transmit signals directly to one in the

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Home Networking Supplement www.cable-satellite.com WiFi mesh.qxd 04/05/2007 11:50 Page 4

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basement, but could do so perhaps via an home mesh has to be totally dynamic and network, it is also highly resilient. intermediate device in the middle of the fluid, able to reconfigure itself on the fly to If one node leaves or is congested, house. MIMO, in turn, would ensure that accommodate the shifting and disappearing traffic is routed elsewhere throughout reliable links with adequate QoS are nodes. the mesh.” maintained between devices within Support for such fluidity has not been Such a mobile mesh poses particular the mesh. necessary for metro WiFi applications, challenges for video, because the typically comprising access points installed reconfiguration or ‘self-forming’ process Fluidity is key on poles or rooftops, but some vendors as devices move around inevitably With a wireless mesh, there are no wires have adopted mobile-mesh anyway to takes time and imposes latency and therefore no cost associated with the provide the added flexibility and be ready constraints. According to Payne, , unless this uses licensed for the home market. One such vendor is PacketHop has addressed these issues spectrum, which would not be the case in the home. However, the allocation and use of spectrum has been a major issue in the evolution of wireless mesh for metropolitan networks and as an alternative to DSL or cable as a local loop for delivering broadband services. In such external networks, the role of meshing lies largely in providing coverage rather than QoS or reliability, for there will often be line of sight between nodes and the objective is to replace wires for interconnecting access points. “Meshing provides integration between wireless access and wireless transport,” notes Park. Early wireless networks, including WiFi hotspots, always comprised access points that were linked back into delivery infrastructure by wired connections. Client devices such as laptops or PDAs would then connect over wireless to the closest access point. The aim of mesh in the first instance is to makes these wired transport connections wireless as well. At present, the wireless transport is confined to the local or metropolitan area, but in principle it could be extended over larger distances, although currently it is questionable whether it would scale well or be cost effective for transmission over remote areas where there would be relatively little access. Within these networks outside the home, mesh has initially been implemented only between “Devices will not always be switched fixed access points, providing coverage between roaming devices inside the zone. on or even present, so the home To have a mesh, there has to be a mesh has to be totally dynamic and minimum of three such points, whereas fluid, able to reconfigure itself on the in the home there is usually just one access point serving all client devices. Therefore, fly to accommodate the shifting and a home mesh would be implemented in the disappearing nodes.” WiFi clients. This changes the game, for while some of the clients might be relatively PacketHop. “Unlike fixed-mesh networks, by ensuring that all devices within range tied to one location, for example a desk ours is highly mobile and the network of each other maintain connection so that bound PC or TV, others, such as laptops or adapts as users come and go within range when one drops out, traffic can be quickly even mobile handsets, would be roving. of the network,” says Kevin Payne, rerouted. The network maintains the Furthermore, devices will not always PacketHop's director of marketing optimum number of video streams be switched on or even present so the communications. “And because it is a mesh at all times.

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www.cable-satellite.com Supplement Home Networking WiFi mesh.qxd 04/05/2007 11:51 Page 5

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“The IEEE 802.11s amendment is with the local loop or metro network. If trying to get the 802.11 mesh network the latter are also wireless mesh based, working at layer two and this seems then it might after all make sense to support layer three routing for end-to-end a very hard issue to cope with, because transport. A likely compromise, according it involves extensions that are very to BelAir's Park, will involve layer two difficult to implement at hardware level.” within the home, but then allocating IP addresses to cross the external network The support for video has been driven Which layer for in-home mesh? at layer three. by PacketHop's customers in security Routing is also simpler within a home mesh, There is the option, however, of and surveillance at the metro level but will which has an impact on the debate over supporting the home mesh as an extension be just as relevant in the home, says Payne. whether it is best to do at layer two or layer of the public or external network, as has Indeed, mesh will only come into its own three. This debate has resurfaced at different already been tried with some community within the home for high bandwidth levels for almost two decades, ever since projects. The user would still appear to applications such as video, Payne asserts. local Ethernet networks started to be have a home network but in practice this “For example, if you were trying to stream interconnected into more complex wide area would just be part of a much larger mesh. video between computers, meshing would mesh-like configurations. Layer two simply For this to work, mesh networks need to offer some advantages because the mesh refers to Ethernet itself, and the process of scale to very large numbers of nodes creates more bandwidth as more nodes/ transmitting data between nodes on a without degradation in QoS. On this front, users are added,” he says. “So potentially fixed point-to-point basis with only limited Microsoft is among the pioneers, having as more devices, such as home enter- support for re-routing in the event of failures developed a new routing protocol called tainment systems, become WiFi enabled, or congestion. Layer three evolved to Virtual Ring Routing (VRR) at its research meshing may offer some advantages.” support more complex routing within mesh laboratory in Cambridge, UK. Meshing could also reduce the chance networks, and therefore comes with the This is an interesting development of temporary breaks in service when a fundamental ingredients for wireless mesh because it takes account of the limited device roams around. A mobile handset networking already built-in. For this reason, range of each hop in a wireless mesh, might be moved into a spot where it is some wireless mesh vendors have adopted with the whole network inevitably out of range of, say, a home PVR streaming the layer three approach, arguing that layer comprising a large number of hops if it video to it, even with the help of MIMO. two needs substantial extension to support has any geographical scale. “This takes a But it might be closer to another device, mesh networking. new approach to routing by merging ideas which in turn is still within range of the But there is also a competitive dimension, for peer-to-peer overlay networks and PVR. So while mesh extends distance with layer two standards being promoted by traditional routing protocols,” says Peter at the metro level, within the home it could the IEEE and layer three by the IETF. “The Key, head of the system and network have the effect of joining up lines of IEEE 802.11s amendment definition is trying group at Microsoft Research (MSR) in communication. to get the 802.11 mesh network working at Cambridge. “Meshes have already been Like MIMO, mesh has the effect of turning layer two and this seems a very hard issue shown to scale to the order of 100s of conflict between signals into cooperation, to cope with because it involves extensions nodes, and we have one of the world's as is noted by Roberto Arcadu, general that are very difficult to implement at largest test-beds in our lab at Cambridge manager of WiNext, which has recently hardware level,” says WiNext’s Arcadu. consisting of over 110 machines.” introduced a home version of its mesh “On the other hand, IETF already proposes However, this is still a long way from solution based on its New Wireless Auto- a complete mesh solution laying on OLSR the size of a full blown metropolitan configurable Device (NAAW) broadband (Optimized Link State Routing) or AODV network, emphasising that these are early access system, which enables any WiFi (Ad hoc On Demand distance Vector) days. As the WiFi Alliance's Hanzlik device to participate in a mesh. “A mesh routing protocols. This is a de-facto standard agrees, it is too soon to tell whether the network is more stable as all the nodes that many mesh network providers around community approach will prevail, or cooperate instead of conflicting, and the the world are already adopting to deploy whether consumers will prefer to have result is a better quality signal and a lower systems in large WiFi covered areas.” their own private home mesh. “There will consumption of energy and less radio Yet within the home, some vendors regard probably be different go-to-market pollution,” says Arcadu. use of such protocols as unnecessary models,” he says. Moreover, some of the problems facing overkill, given that there is not that much The whole issue of spectrum allocation mesh networks over a larger geographical real routing to be done. “Layer 3 in the then arises, with the intriguing possibility scale do not arise within most homes. home would be a big mess,” insists Matt of convergence or integration between the “Because the range is limited in the home, Holdrege, technical director of the wireless licensed spectrum used in public networks, performance may actually improve,” says mesh pioneer Strix Systems. and unlicensed spectrum as used by WiFi PacketHop's Payne. “A mesh network in the at the home or neighbourhood level. home wouldn't be likely to face the Integrating home WiFi networks Amid all these debates, there is interference or usage challenges that a But this raises another issue, which is agreement at least that the home mesh will metro WiFi would face.” how home WiFi networks will integrate come to market one way or another. CSI

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