Sample Topologies
Basic topologies

There are several basic physical configurations that can be used in a WLAN deployment. This section will discuss the following primary WLAN topologies:

  • Peer-to-Peer (Ad Hoc) Topology (IBSS) – As Figure shows, a wireless service set can consist of nothing more than two or more PCs, each with a wireless network card. This configuration, which does not include an AP, is called an Independent BSS (IBSS). Operating systems such as Windows 98 or Windows XP have made this type of peer-to-peer network very easy to set up. This topology can be used for a small office or home office, to allow a laptop to be connected to the main PC, or for several individuals, to simply share files. However, coverage limitations are a drawback in this type of a network since everyone must be able to hear everyone else.
  • Basic Infrastructure Topology (BSS) – The basic service set (BSS) is the building block of an 802.11 LAN. Figure shows a BSS with three stations that are members of the BSS, in addition to the AP. The BSS covers a single cell, as indicated by the circle. When a device moves out of its BSS, it can no longer communicate with other members of the BSS. A BSS uses infrastructure mode, a mode that needs an access point (AP). All stations communicate through the AP. The stations do not communicate directly. A BSS has one service set ID (SSID).
  • Extended Infrastructure Topology (ESS) – An extended service set (ESS) is defined as two or more BSSs that are connected by a common distribution system, as illustrated in Figure . This allows the creation of a wireless network of arbitrary size and complexity. As with a BSS, all packets in an ESS must go through one of the APs.
  • Dial-up – The dialup topology is designed for the small office/home office (SOHO) market. It allows telecommuters, SOHOs, and home users the convenience of wireless connectivity via an AP, as shown in Figure . In fact, some APs are less than $50 USD. Shared dialup connectivity allows both wired and wireless devices access to the modem and the Internet. A PC running Windows 2000 or XP Internet Connection Sharing provides the connectivity and also functions as a DHCP server for the wireless clients. Unfortunately, even though dialup is quite inexpensive, it is quite slow compared to the latest broadband technologies. Many consumers are choosing to go with broadband technologies if available.
  • Broadband – With greater availability of broadband services such as cable, DSL, wireless and satellite, many users are switching from dialup to broadband. Also, users are now installing home networks in order to share the high speed Internet connection as well as local file and print services. The basic home network topology consists of the "modem", a router, a hub/switch, a wireless AP, and clients. In some cases, the router, switch, and wireless AP are housed in a single unit called a wireless router.

There are still many broadband users with a standalone PC directly connected to the Cable or DSL modem. Since users are directly exposed to Internet attacks, this simple but insecure topology should be secured by some type of hardware or software firewall. Without any protection, the PC many "open" TCP ports will soon be compromised by attackers. Even if users do not have any valuable information on the PC, the device can be used to assist attackers to compromise other networks.

Wireless routers typically support both Cable and DSL, as Figure shows. In this topology, the AP or wireless router will support the wireless clients, while the built in switch supports the wired devices. Other services such as DHCP and Network Address Translation (NAT) are provided by the router. NAT enables multiple LAN devices using private IP addressing to share a single public IP address. Many vendors are also including firewall features such as access control, filtering and stateful inspection to protect the LAN devices from attackers. In addition to the wireless security issues, home users with an "always on" Internet connection are more prone to attackers.


Interactive Media Activity

Interactive Activity: Name that Topology

This activity is a game where the student must choose the correct name for a slowly forming topology as fast as possible. The goal is to type in the LETTER that corresponds to the correct name of the current topology as fast as possible in the text box.