Cluster Multiple Access points – A peek at Wireless Clustering for Unified Management

Well, you want to go with a reliable and simple wireless solution for your organization. But your’s is not a small one for a single/ couple of stand alone access points. Neither is it a big one for going with wireless controller managed access points. Your requirement is to provide wireless coverage for around 100 people by having five to six access points, but you want the wireless technology to be reliable as well as cost effective. Wireless Access Points Clustering, may be the answer for you! Read on to find out more…

Architecture/ Block Diagram for Wireless Access Points Clustering
Architecture / Block Diagram for Wireless Access Points Clustering

Unlike wired networks which are quite simple to predict and build, wireless technology has always been tricky – you just cannot predict the coverage area or the bandwidth levels! Worse, it keeps changing frequently. Some times there are disconnections, some times the wireless network is slow, some times users don’t get signals properly! If you have multiple stand-alone access points, this might have been your experience. Getting a wireless controller might be the best answer, but its not a cost-effective option.

So, when you analyze the options – there are chances that you might have totally missed Clustering Access Points because very few vendors provide products supporting this nice technology!

So, What is Wireless Access Point Clustering?

Cluster, as the meaning goes, is a group which works in unison. So, the ability of the Stand-Alone Access Points to form a dynamic configuration aware group with similar access points (Read: same model, same vendor) is called a Wireless Cluster. A Wireless Cluster provides single point of administration for all the Access Points configured in the cluster mode in the same network. That means, you just need to configure one access point, and the remaining access points in the same cluster will borrow the configuration details from the first one. Not only that, when you need to make changes to the configuration of all the access points in the cluster, you just make them in one of the access points – the remaining will auto-sync all the changes.

An Access Point can even form a cluster with itself (cluster of one member). But for more than one clustering enabled access points, clustering can be achieved if,

  • All the Access Points are from the same vendor and the same make – they should support the wireless cluster technology.
  • All the Access Points should be in the same LAN (subnet).
  • They should have same radio (some vendors support dual radio as well) and band (2.4 Ghz or 5 Ghz) configuration.
  • Well generally, 8-10 Access Points can form such clusters depending on how many the vendor supports. The other stand-alone access points can reside on the network as stand-alone access points and this does not affect the cluster. Multiple clusters in the same network are supported by some vendors.
  • Generally, each Access Point can be individually selected/ not selected to join a cluster. A cluster also has its unique name and if there are going to be multiple clusters, all the access points in each cluster should have the same name.

What are the advantages of Access Point Clustering?

The main advantage is that multiple stand alone access points can be managed as one entity instead of having to configure settings in each of them separately. When one of them is configured/ re-configured, all of them pick up the settings and configurations from there. The cluster settings in some models allows to check if any changes have been made in the cluster access points every hour (or some other duration, that can be selected).

Another important advantage is Roaming. Clustering multiple access points allow wireless clients (laptops, wi-fi phones, wi-fi cell phones) to roam within any of the clustered access points without having to disconnect and with a very fast hand over time (in milli-seconds) so that even calls being made on the wireless IP network can continue without interruptions when the clients roam from one access point to another (clustered mode).

Clustering enables Automatic Channel Assignment: Well, with stand-alone access points, this is a big dis-advantage as they select the channel of operation (sub-frequency in the given spectrum) by themselves in a random fashion (without checking for the channels in which neighboring access points operate in). This results in interference, frequent disconnections, etc. And what makes is worse is that the commonly used 2.4 Ghz spectrum has only three non over lapping channels (2,6,11) and the neighboring access points should work in one of these three but should not select the same channel as well!  But with clustering, automatic channel assignment can be enabled in which each access point checks the channel of operation of the neighboring access points and adjusts its frequency accordingly so that there would be minimum interference. The channels assigned to each cluster member can be viewed, and if required locked manually.

The configuration/ settings for the following can be generally managed by a cluster (not all vendors support all the below settings, but this is a generic list):

  • Wireless Network Name (SSID)
  • Administrator Password
  • Configuration Policy
  • Wireless Interface Settings
  • User accounts and Authentication
  • Network Time Protocol Settings
  • Radio Settings (Mode, Channel, Fragmentation Threshold, RTS Threshold etc)
  • Basic security settings/ MAC address filtering tables
  • QoS settings

Limitations of Wireless Access Points Clustering:

  • It is supported by a very few vendors, and in particular models only (all the cluster AP’s should be of the same vendor and model).
  • There are no standards for this technology, and is generally proprietary to the vendor.
  • Has not been adopted on a large scale.
  • IP addresses, MAC addresses, Location Info, Load balancing Info etc. are not shared between the cluster members (for those settings not shared by cluster members, the configuration should be done individually in each AP).
  • There is a limit to the maximum number of access points that can form a cluster (generally 8 or 10)
  • Sometimes the access points need to be in the range of at least one of the cluster AP’s.

Related Article: Everything you wanted to know about Wi-Fi Networks – Architecture/ Block Diagram and Components

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