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Introduction

Wireless LAN's are deployed in many and varied different manners. It is important to understand the different charateristics and issues associated with each WLAN deployment environment and architecture configuration.

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WLAN Deployment Environments

Private Wireless LAN Networks

Private WLANs refer to wireless networks privately deployed by corporations for internal employees’ usage. Similarly, wireless networks are defined private when deployed by other institutions or organizations, as well as by individual households, for their own personal usage.  A prerequisite for private WLAN is security. Given the relevance and confidentiality of the information that flows within a company, security must be guaranteed; in addition access is rigorously restricted to a limited number of users (employees, members of the organization/institution/family). Specifically, access is granted only to a controlled number of MAC addresses assigned to WLAN cards. The authorized MAC addresses are defined in a database within each access point. Security still represents the major obstacle to the widespread adoption of WLAN inside corporations. Once security is guaranteed, corporate usage of WLAN will grow exponentially, as the advantages compared to the efforts of implementation are undoubtedly significant.

Semi-private Wireless LAN Networks

Semi-private are those WLANs deployed in organizations or institutions open to the public, such as University campuses and high schools. Potential users of these networks are not only the members of the institution (students, teachers, etc.) but also other people who approach the institution and have the right equipment (everyone with a laptop or other wireless device and a wireless card). People are not charged for accessing the Internet via a semi-private network. However, unlike in private WLANs where companies provide their employees with the laptop and the wireless cards, in the semi-private wireless networks institutions are not supplying the wireless cards to the users. In fact, they are limiting to make the technology available and open to whom ever values it.

Public Access Wireless LAN Networks

Public Access WLANs are wireless networks deployed in highly frequented places, such as airports, hotels, convention center, cafés, etc. The main difference with private or semiprivate WLANs resides in the fact that users are charged for accessing broadband Internet. There are various business models implemented upon this type of network, the most popular of which consist in charging customers either a flat monthly fee or a per usage fee.

Community Wireless LAN Networks

Community networks imply sharing broadband Internet connection (like DSL or cable modem). There are different levels of sharing the high speed Internet connection. A limited sharing is when a WLAN is deployed in a neighborhood and two or more neighbors are splitting the costs of the equipment and the monthly broadband Internet access fee. The reasons for doing this are generally the difficulty for some of the residents in a neighborhood to get broadband Internet or to save money by dividing the costs for the broadband access.

WLAN Deployment Architectures

Independent Ad-Hoc Network

A set of stations that communicate in a Wireless LAN is called a Basic Service Set (BSS).  It is the logical connection between the stations that determines a set, no the proximity of the stations.  A network architecture where these mobile stations directly talk to each other and are not connected to a wired network, e.g. the Internet or the corporate LAN, is an Independent BSS (IBSS).  These stations can only talk to each other and build their own LAN.

In this IBSS, a station can only communicate with another station if they are in direct radio contact with each other.  In the basic IBSS there is no provisioning of a relay.  This limits the coverage area of these networks considerably.  Normally, there is no central hub that all stations connect to and the connections are established on an impromptu, per need basis.  In such a case the network is called an Ad-hoc Network, which is generally relatively small and short-lived.  For example, at a conference one could access the presenter’s computer and communicate with him/her, ask questions and download the presentation file without having to log onto the conference center’s private network.  In a collaborative setting, one could work together with colleagues on a document or presentation in a meeting.  A sales person can exchange information material wirelessly with a client or vendor when in the field.

Centralized Networks (with AP)

A BSS that includes a central access point (AP) where all stations connect to, is no longer independent and referred to as an infrastructure BSS.  All mobile stations need to communicate with the usually stationary AP to be able to exchange information.  The AP functions as a relay for the stations as well as a gateway to the wired network if attached.

In this constellation, all communication from one AP to another needs to go to the AP and back to the required station.  This in turn doubles the bandwidth needed for intra-BSS communication compared to a direct connection between APs.  However, it is a minor drawback compared to the benefits of this architecture.  First, the AP coordinates traffic and enables roaming.  Second, by buffering traffic to and from one station an AP makes power management feasible.  Third; authentication and authorization performed by an AP makes access to the wired network secure.

Extended Service Set (ESS)

To achieve a greater mobility of mobile stations and not confine them to a single BSS, multiple infrastructure BSSs can be combined to form an Extended Service Set (ESS).  A distribution system (DS) connects the APs, forwards traffic, and facilitates the movement of mobile stations within a larger area.  This DS does not need to be a network, and can be wired or wireless, but needs to fulfill certain functions.  In the AP it determines whether received information needs to be relayed in the BSS, forwarded within the ESS or sent to the wired network for communication with outside entities.  The DS also hides the mobility of the stations by combining the whole ESS into a single-MAC network, which makes it possible to use existing network protocols to make sense in mobile settings. 

Infrastructure BSSs and ESSs are very versatile and widely deployed.  It is the WLAN of choice for extending the wired corporate network, used in public access WLANs and most SOHO installations. 

Additional Resources:
See: Public Access WLAN
WLAN System Components
WLAN Roaming
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