Understanding Wireless LAN Switching
for Wi-Fi Wireless LAN Centralized Control and Management

Connect802 can help with the selection and system design for many manufacturer's wireless LAN switch equipment. We are also an authorized, value-added reseller for a number of major manufacturer's products.

If you have questions, please don't hesitate to call us today! We'll be happy to provide you with any technical explanation that you need to help you assure a successful wireless networking deployment.

Access Points and Wireless LAN Switching

An Access Point contains both a radio circuit and 802.11 processing intelligence

A typical 802.11 network may have many Access Points that connect back into the core Ethernet network through one or more Layer 2 Ethernet switches (standard Ethernet switches). This is referred to as the "wired distribution system" and, for a particular group of Access Points, a single wireless LAN is created (because each Access Point has been configured to advertise the same network name, "SSID").

An Access Point contains both a radio circuit (2.4 GHz or 5.8 GHz transmitter/receiver) and on-board intelligence capable of processing 802.11 control and management information plus the ability to encrypt and decrypt frames as well as a capability to communicate to an authentication server (802.1x / RADIUS) to confirm the identity of a user trying to access the network. This combination of radio+intelligence is Ethernet-attached to the core network's Ethernet switch.

The radio circuitry stands alone in the Wireless LAN Switch system,
with processing intelligence moved to the central switch device

Now, lets redesign things slightly. Let's move some (or all) of the intelligence out of the Access Point's case and into the Ethernet switch. This is going to require some specialized communication between the stand-alone radio circuitry and the central switch controller. And so it is when we talk about a "Wireless LAN Switch". The advantages of a Wireless LAN Switch system generally result from this centralization of intelligence for all the radio transceivers. Wireless LAN Switching may provide:

• Awareness of the physical location of a mobile device based on signal strength triangulation
• Automatic recognition of a failed Access Point and autorecovery through automatic reconfiguration of the entire system
• Intrusion detection and rogue blocking (since all Access Points are known to the central switch)
• Preemptive roaming, in which the Access Points can share information about when to hand-off communication to a particular moving client

The Difference Between Stand-Alone Access Point Systems and Wireless LAN Switching
	Stand-Alone Access Point An 802.11 Access Point contains a radio circuit and the intelligence to process 802.11 management and control information as depicted inside the red oval in the diagram on the left. The standard Layer 2 Ethernet switch, serving as the central connection point, simply forwards Ethernet packets. Access Points can't easily convey configuration or security information to each other since no standard protocols exist to perform these functions. Each Access Point operates as an independent device.
	Wireless LAN Switch In a Wireless LAN Switch system most of the intelligence is moved from the remote Access Point into the centralized switch. The remote "box" is, essentially a radio transceiver and the central switch performs both Layer 2 Ethernet switching and controls the remote radios as depicted in the diagram on the left by the fact that the intelligence is now in the central switch device. Since some, or all, of the 802.11 management and control functions are moved to the central device each Access Point operates in harmony with all others and the system functions in a manner that can be generally though of as one very large antenna system.

Preemptive Roaming

Consider the situation where a user is downloading their email while they're walking down the hallway from their office to a conference room (or, perhaps, while a wireless VoIP telephone user is walking across the corporate campus). The mobile device is initially communicating to the wired network through some particular Access Point. Now the mobile device is moving away from that Access Point (and, hopefully, towards an area covered by some other Access Point). The default behavior for an 802.11 device is to reduce transmission speed as signal quality degrades. This means that the mobile device will reduce its speed down to 1 Mbps (in an 802.11b environment) and only then will the device attempt to synchronize/associate with the next Access Point. This roaming behavior is controlled by the mobile client device. The Access Points involved have no awareness of the location of the client relative to one or the other.

When Wireless LAN Switching is being used the central switch can maintain an awareness of the signal level being received from each mobile device by each radio. Hence, instead of having to wait until the last possible moment (as per the 802.11 standard) the mobile device can be handed off by the Wireless LAN Switch. Hence, users in a Wireless LAN Switch environment experience a more consistent data rate as they roam through the area. Their mobile devices don't need to wait until the "last possible moment" (with the resulting lowest possible bit-rate) before they reassociate to the "next" Access Point.

Legacy Hand-Off Behavior Compared to Preemptive Roaming

The mobile device (position 1) is going to move to the right towards Access Point "B" Notice that the coverage area for Access Point extends to A' and the coverage area for Access Point B extends to B' The point where the signal is equal from A and B (position 2) is the ideal place to change-over from one Access Point to the other. The mobile device, however, will wait until it reaches the edge of the coverage area (position 3) before it changes its association, and that means the device waits until it's in the lowest bit-rate zone before a hand-off occurs. Preemptive Roaming would cause the hand-off to occur at Position 2 under the control of the Wireless LAN Switch, rather than at Position 3 where it would occur when under the control of the mobile device.

It's Not Called and "Access Point" Anymore

Vendor	Term Used for Radio Device
Aruba Networks:	Access Point
Cisco Systems:	Thin Access Point
Symbol:	Access Port
Trapeze:	Mobility Point
Other Vendors:	Lightweight Access Point

Definitions and descriptions of Wireless LAN Switches that you might find on the web:

• The term switch is a bit of a misnomer, because while the WLAN switch offers similar management and control functions as a wireline switch, it doesn't do so on a port-by-port basis and it doesn't provide dedicated bandwidth to an end user. An exact parallel essentially would require dedicating a single blast of wireless coverage per user. Until that happens, the term switch will have to suffice for the current generation of product.
• Wireless LAN switches use multiple, separate directional antennas that send signals in different directions at the same time. This enables simultaneous, collision free transmission among clients associated with the same access point. This means that more users can associate with the same access point at longer ranges and attain higher overall throughput (due to less contention with other users). [Note: This definition refers to an antenna technology that is NOT the same as the "Wireless LAN Switching" being discussed here!]
• Many existing wireless LAN switches are really doing nothing more than managing access points, there's not much intelligence in them, and all the intelligence is in the access point. If the design of the access point decouples RF capabilities from IP addressing and memory processing, and put the latter functions into the central switch the result is that you have IP addressing happening in the switch, and any application server functions. It's a branch office in a box and what you are left with is very inexpensive access points that make it easier for you to decide about expanding Wi-Fi to branch offices.
• Some vendors have a layer-2 solution for the wireless users, which means that the Access Points need to be directly connected to their "switch". This greatly reduces the deployment options and is often not in line with the enterprises networking designs. Other vendors offer AP's, that are able to be deployed anywhere in the network, LAN or WAN, and even across layer 3 boundaries. They automatically create a generic routing encapsulation (GRE) tunnel back to the switch wherever it resides in the network. Capital and operational costs are low because, even for a 4000-user population, only one switch is required.
• Some AP's are truly thin because they process nothing of the 802.11 frame. The entire frame, including the admin portion, is passed in its entirety to the WLAN switch which would then perform all the needed functions for the network (security, management, mobility, RF controls, etc). This approach is less complex to configure, and for troubleshooting the switch then has all required information at hand because it received the entire 802.11 frame. New 802.11 standards (except RF ones) are done in the switch only, while security and maintenance rule issues are centrally managed.
• A wireless LAN switch describes a configuration where the functions of a number of specially designed “thin” access points are coordinated through a central server. While the level of sophistication varies from product to product, wireless LAN switches will typically incorporate a mechanism for managing the radio domain. They usually come with tools that allow them to insure adequate radio coverage, identify problem areas, and facilitate network upgrades. In wireless LAN switch environment, when a new access point is added to the network, the transmit power of the surrounding access points is automatically adjusted to reduce interference and maximize performance. Further, as the central controller will know all of its access points, it can quickly identify “rogue” access point installed by users. Besides managing the radio domain, wireless LAN switches can also centralize security management and record keeping and provide a solution that is geared toward large-scale commercial implementations.

You may read about centralized encryption models, seamless and secure mobility, WLAN scalability, synchronized encryption keys, and other real-time communication's features to support secure 802.11 networking. In many cases you're reading about features associated with Wireless LAN Switches. Ever wonder how rogue AP detection and classification or automatic client and AP intrusion detection algorithms work? Wireless LAN Switching is probably part of the equation. Connect802 provides two unique wireless LAN switching solutions (symbol technologies and trapeze networks) to meet your required level of functionality and sophistication. In addition, we have standard access point implementations when wireless LAN switching is not required. We've Got You Covered!