With traditional Wi-Fi networks, access points form radio cells that provide wireless connectivity to users, and these access points require cabling that interconnects them with Ethernet switches to enable roaming and connections to servers and the Internet. This is the most common wireless LAN configuration, but a problem for many applications is that it’s costly and not feasible to run cabling to each access point. As a result, vendors such as BelAir Networks, Firetide and Tropos Networks are delivering mesh networking solutions to ease installations where cabling gets in the way.
In general, mesh networking replaces the access points with “backhaul nodes” that are entirely wireless, except for the electrical cord. One side of the node interfaces with Wi-Fi users, typically via 802.11b/g. The Wi-Fi user associates with the mesh network node just as it does with an access point. The other side of the backhaul node has radios that interconnect the node to other backhaul nodes that comprise the mesh network.
BelAir Networks, for example, has a mesh solution that includes backhaul nodes having a circular antenna array consisting of eight high gain antennas and three radios. The radios operate independently and have automatic and adaptive antenna selection mechanisms for making the most efficient interconnections and topologies. This eases installation and accommodates changes in the radio environment. The nodes deliver traffic throughout the backhaul network over non-2.4GHz frequencies to maximize capacity.
The operation of a mesh network is fairly straightforward. For example, the URL request from a Wi-Fi user enters the mesh network at the back haul node that the user associates with using Wi-Fi protocols and then hops from one node to the other until it reaches the node that connects to the Internet service provider. In some cases, the data packets may hop only a couple of nodes, but a greater number of hops may be necessary in larger networks. Thus, the time it takes for the corresponding web page to return to the user will vary depending on the layout of the network.
A mesh network offers multiple paths from source to destination, and intelligent routing algorithms allow each node to makes a decision on which path to forward packets through the network in order to improve performance. If the link between a pair of nodes along one of the paths is clogged, for example, then the algorithms establish another path that avoids the congested link. Also, if a node goes down, an alternate route is chosen based on the routing algorithms.
This makes mesh networks suitable for areas where it’s not feasible to install a traditional wireless LAN consisting of access points. For example, a mesh network approach makes sense to consider for residential and city-wide (“muni,” short for municipal) Wi-Fi networks. The deployment of cabled access points over larger, open areas is a daunting task because of the massive amount of data cabling that requires installation and the countless permissions that you must receive. Other places where installation is difficult includes convention centers, college campuses stadiums, marinas, parks, and construction sites. Simply plop in the backhaul nodes where coverage is necessary, and automatic mechanisms connect the node into the network.
A mesh network is also worthwhile when installing a temporary wireless network because the backhaul nodes are faster to install and there’s less to remove. For example, emergency crews can quickly establish a mesh network when working at a disaster site. Enterprises can also benefit from mesh networks when needing network connectivity in temporary work areas.
Another good fit is within buildings that don’t have existing data cabling for access points. The costs of installing cable are very relatively high, especially when there are requirements for conduit for enclosing the cabling, which is commonly the case. The conduit alone generally doubles the cost of installing access points. In this case, the deployment of a mesh network can save hundreds of dollars per access point.
Mesh networks, however, are not yet ready for wide-scale installation in large enterprises, mainly because there are no official standards for mesh networks. The development of the 802.11s standard, which addresses mesh networks, is in process with a possible draft available within the next year or so. But, based on the history of the 802.11 group with other standards, such as 802.11n, we’ll likely be waiting for a couple years. There are currently dozens of 802.11s proposals, which means that the mesh equipment that you buy today will likely be obsolete after ratification of the 802.11s standard. Enterprises shouldn’t invest in this type of technology until standards are firmer.
The mesh network solutions on the market today all differ widely. As a result, you must carefully analyze each solution and ensure that it satisfies requirements before moving forward. The current state of the mesh network market is somewhat worse than 802.11n in terms of stability. At least with 802.11n, we’re down to two competing proposals, and 802.11n doesn’t address as much of the network architecture as mesh networking does. Therefore, one should be very wary of performance, security, and management of existing mesh network solutions.
Latency, for instance, may vary significantly, depending on the number of users and hops that are necessary for moving packets through the back haul network. Roaming and routing delays may offer performance issues, especially for VoIP applications. Even if the data rate between the user and the local backhaul node is kept high, which many of the mesh network vendors claim, the delays across the network may be substantial. A mesh network, though, will likely deliver much better performance than existing 3G systems.
In some cases, the benefits of a mesh network far outweigh the issues. If you need a robust Wi-Fi solution where it’s not feasible to run cable to access points, then a mesh network is the answer. Lower installation costs because of less cabling and increased utility in difficult-to-wire areas make mesh networks shine. There are a few wrinkles to iron out with the standards and better provisions for VoIP, but mesh networks certainly have a permanent home in the wonderful world of wireless.
Jim Geier is the principal of Wireless-Nets, Ltd., a consulting firm focusing on the implementation of wireless mobile solutions and training.
