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AIS300 - Scheme of Work - Scholarly Commons Home

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2005). The first advantage <strong>of</strong> this mode is the simplified, easy and quick WLANs<br />

formation by consenting nodes without having to rely on other medium such as AP.<br />

The second advantage is in the minimal hardware and network management<br />

requirements (Housley & Arbaugh, 2003). The main disadvantage <strong>of</strong> Ad hoc WLANs<br />

is the inability <strong>of</strong> wireless nodes to connect and communicate with other networks<br />

without applying additional routing protocols (Housley & Arbaugh, 2003; Tyrrell,<br />

2003). Figure 2.1a represents the simplified Ad hoc WLANs architecture.<br />

a) Ad hoc<br />

Figure 2.1 WLAN architecture a) Ad-hoc (IBSS) and b) Infrastructure (ESS)<br />

The infrastructure BSS is more popular among the current WLAN users compared to<br />

the IBSS (Housley & Arbaugh, 2003). Infrastructure BSS can be used to create<br />

WLANs coverage in homes and small <strong>of</strong>fices that have access to the wired LANs. In<br />

the infrastructure BSS, the WLANs will comprise <strong>of</strong> at least one access point (AP) that<br />

links to a group <strong>of</strong> wireless nodes and also to the wired LANs. In the infrastructure<br />

mode, the AP acts as an Ethernet bridge for all communications that occurs between the<br />

wireless nodes and also for communication that occurs between the wireless nodes and<br />

the distribution system (DS) located at the wired LANs (Tyrrell, 2003). The DS is<br />

defined as an interconnection networks that combines several BSS to form a single<br />

logical network (Schafer, 2003). In the infrastructure WLANs environment, there will<br />

exist at least one set <strong>of</strong> BSS (Arbaugh, 2003; Housley & Arbaugh, 2003). Figure 2.1b<br />

represents a simplified infrastructure WLAN configuration where BSS1 and BSS2 are<br />

5<br />

AP1<br />

INTERNET<br />

ROUTER<br />

HUB<br />

b) Infrastructure<br />

AP2

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