Network Security Fundamentals [Electronic resources] نسخه متنی

Different WLAN Configurations

As you will see in the case study at the end of the chapter, wireless network connectivity is not limited to corporate enterprise buildings. WLANs also offer connectivity outside the traditional office environment. Numerous wireless Internet service providers are appearing in airports (hotspots), trains, hotels, and conference and convention centers.

As with most technologies, the early wireless networks were nonstandard, and only vendor-proprietary technologies existed. This caused interoperability issues between the different standards of WLAN technologies with vendor-specific implementations. Standards-based WLAN technologies were developed because of the interoperability issues. Today, several standards exist for WLAN applications: 802.11, HiperLAN, HomeRF Shared Wireless Access Protocol, and Bluetooth. This chapter focuses on the 802.11 implementations, which are the most widely used.

For an end user, WLANs can be categorized as follows:

• Peer-to-peer

• LAN

• Hotspots

For a network administrator, WLANs can be categorized as follows:

• Point-to-point bridge

• Point-to-multipoint bridge

• Ethernet to wireless bridge

One of the earliest setups for WLANs was in peer-to-peer WLAN configurations. Wireless clients equipped with wireless network interface cards (NICs) communicate with each other without the use of an independent network device called an access point. These wireless NICs exist in different types: card bus, Personal Computer Memory Card International Association (PCMCIA), and Peripheral Component Interconnect (PCI). Peer-to-peer LANS have limitations such as limited coverage area and lack of access to wired resources.

NOTE

Among the first wireless devices were laptops with built-in infrared ports. Many peer-to-peer transfers were accomplished successfully over these ports to replace null modem cable transfers. Now Ethernet crossover cables accomplish this purpose.

Figure 14-1 illustrates the peer-to-peer WLAN configuration.

The peer-to-peer WLAN is often referred to as the independent basic service set (IBSS), as discussed later in the chapter.

A multiple-segment WLAN extends the coverage of a peer-to-peer WLAN through the use of overlapping zones or areas. The coverage area of a zone is determined by the characteristics of the access point (a wireless bridge) that coordinates the wireless clients' use of wired resources.

Typical examples of these zones are hotspots in airports, coffee shops, and hotels. Your hotel provides access in the room, in the restaurant, in the lobby, and in the conference rooms. You are able to roam about without losing the connection. Figure 14-2 shows the setup of a wireless hotspot.

The hotspot WLAN is often referred to as the infrastructure basic service set.

NOTE

An extension of these hotspots is found in community networks. These types of networks extend Internet access with free access. The purchase, installation, and maintenance are taken care of by the community. Community networks can extend to include schools, neighborhoods, and small businesses. It has been noted recently that community networks are not limited to certain areas; instead, wireless community networks are popping up worldwide.

A full database of worldwide deployments of wireless community networks can be found at http://www.nodedb.com.

Imagine that Company XYZ acquires Company ABC, which is located in the same business park. The network administrators have the responsibility to establish connectivity between the two companies and integrate Company ABC's infrastructure into Company XYZ's infrastructure. Building-to-building wireless networks might be an option to address the connectivity requirement between LANs (buildings) in a campus-area network.

There are two different types of building-to-building wireless networks:

• Point-to-point

• Point-to-multipoint

Point-to-point wireless links between buildings can be either radio- or laser-based point-to-point links. Figure 14-3 illustrates the point-to-point wireless setup between two buildings.