Colubris LMP: Extending hotspot reach

By Lisa Phifer

July 25, 2007

We create a network running the new Local Mesh Protocol. The results: Easier, cheaper deployment, better connectivity.

Despite competition from 3G and WiMAX, the Wi-Fi hotspot market continues to grow, fueled by mobile worker demands for high-speed Internet access to both data and voice services. But, in many public access venues, network infrastructure costs and complexities make it hard to expand hotspot capacity and coverage.

To simplify this, Colubris Networks recently added a new Local Mesh Protocol (LMP) to its MultiService Access Points (MAPs) and MultiService Controllers (MSCs). Using LMP, we quickly created a 5-node Colubris hotspot, interconnected by a self-healing Dynamic Wireless Distribution System to a single wired backhaul link. However, we were unable to centrally provision or monitor our local mesh hotspot—a key enhancement that Colubris expects to ship this October.

Colubris MSC 3300 ($1,099)
Colubris MAP-330 ($699)
5-node Local Mesh as tested: $3,895
Colubris Networks, Inc.
Waltham, Massachusetts
http://www.colubris.com
Colubris APs

Making a mesh

Many hotspot operators are already familiar with Colubris MAPs and MSCs. Today, Colubris sells half a dozen MAP models with single or dual radios, for indoor or outdoor use. This fall, Colubris expects to start shipping a new 802.11n MAP as well. In our test mesh, we used four MAP-330s with dual a/b/g radio APs that support up to 16 Virtual Service Communities (VSCs), each with its own SSID and QoS/security policy.

Colubris WLANs can be controlled in several ways. For example, Colubris 5000 series MSCs can provide access control and management for up to 200 MAPs/2000 users. Colubris 3000 series nodes combine MSC and MAP functionality to yield "hotspot in a box" solutions for up to 100 users. We chose a single MSC 3300 as our fifth (Master) AP—and the only node in our test mesh to have a wired Internet drop.

On each mesh node, we configured one radio with user-accessible 802.11b/g VSCs: an open "GuestNet" VSC requiring web authentication, a WPA2-encrypted "CorpNet" VSC requiring 802.1X authentication, and a MAC-authenticated VSC for tester access (see below). To focus on LMP, we stuck to these basic VSCs and did not attempt to exercise the more advanced QoS/WMM or VPN capabilities of our Colubris nodes.

To connect our MAPs to each other and the MSC, we configured each node's second radio to participate in an AES-encrypted 802.11a Dynamic Wireless Distribution System (DWDS) group (see below). Our tests focused largely on set-up and operation of this self-healing wireless backhaul mesh and its impact on administration and usability.

Test network

To avoid competition with our 802.11b/g public access hotspot, we chose to dedicate each MAP's second radio to 802.11a backhaul, secured by WPA2-PSK, without WMM. But we could have applied any radio, protocol, security, or QoS profile supported by our MAPs—for example, using WMM to prioritize VoIP across the mesh—so long as all DWDS group links share the same frequency, channel, and keys.

Overcoming static backhaul barriers

In past Colubris OS releases, MAPs could be inter-connected by static WDS links, nailed up between nodes. But if a static WDS node fails, all downstream MAPs are left high and dry. If one static WDS node changes channels to avoid interference, there is no guarantee that other MAPs will change to the same channel at the same time to preserve the mesh. These factors can make static wireless backhaul links unreliable and very hard to manage remotely. But the conventional alternative—Ethernet drops to every node—can be expensive or impractical in venues with hard-to-wire expanses.

In COS v5, Colubris added a Local Mesh Protocol (LMP) that MAPs can use to discover other dynamic WDS nodes, automatically forming the best possible backhaul links and healing the mesh without administrator intervention after failure or RF change. We found these improvements significantly reduced the effort associated with MAP installation and footprint/performance tuning. For example:

  • When we placed a MAP too far from the mesh to sustain a reliable link, we could easily reposition that MAP without relocating an Ethernet drop.
  • When we wanted to extend our test mesh's footprint to another building 50 yards away, we just carried a MAP next door and plugged it into an AC outlet.
  • When an external 802.11a AP was placed near our MSC to create channel competition, the MSC shifted the entire mesh to a friendlier channel.
  • With few exceptions, when a MAP was "accidentally" rebooted or unplugged, the mesh reformed itself to work around the lost node within minutes.
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