A WLAN using more than one AP [that is, an ESS (Extended Service Set) WLAN] requires careful planning to prevent the APs from interfering with one another while still servicing a desired coverage area. Specifically, an overlap of coverage between APs should exist to allow uninterrupted roaming from one WLAN cell (which is the coverage area provided by an AP) to another. However, those overlapping coverage areas should not use overlapping frequencies.
Figure 12-9 Coverage Overlap in Coverage Areas for Nonoverlapping Channels
Figure 12-9 shows how nonoverlapping channels in the 2.4GHz band can have overlapping coverage areas to provide seamless roaming between AP coverage areas. A common WLAN design recommendation is to have 10% to 15% overlap of coverage between adjoining cells.
Figure 12-10 Nonoverlapping Coverage Cells for the 2.4GHz Band
If a WLAN has more than three APs, the APs are deployed in a honeycomb fashion to allow an overlap of AP coverage areas while avoiding an overlap of identical channels. The example in Figure 12-10 shows an approach to channel selection for adjoining cells in the 2.4GHz band. Notice that cells using the same nonoverlapping channels (channels 1, 6, and 11) are separated by another cell. For example, notice that none of the cells using channel 11 overlap another cell using channel 11.
Note: Although a honeycomb channel assignment scheme can be used for the 5GHz band, identical channels should be separated by at least two cells rather than by a single cell, as shown in figure 12-10 for the 2,4GHz band.
About The Author
Anthony Sequeira, CCIE No. 15626, is a Cisco Certified Systems Instructor (CCSI) and author regarding all levels and tracks of Cisco Certification. Anthony formally began his career in the information technology industry in 1994 with IBM in Tampa, Florida. He quickly formed his own computer consultancy, Computer Solutions, and then discovered his true passion-teaching and writing about Microsoft and Cisco technologies. Anthony joined Mastering Computers in 1996 and lectured to massive audiences around the world about the latest in computer technologies. Mastering Computers became the revolutionary online training company, KnowledgeNet, and Anthony trained there for many years. Anthony is currently pursuing his second CCIE in the area of Security and is a full-time instructor for the next-generation of KnowledgeNet, StormWind.com. Anthony is also a VMware Certified Professional.
CompTIA Network+ N10-008 Cert Guide contains proven study features that allow you to succeed on the exam the first time. Expert instructor Anthony Sequeira shares preparation hints and test-taking tips, helping you identify areas of weakness and improve both your conceptual knowledge and hands-on skills, essential for successful completion of the performance-based testing items on the exam. This complete, CompTIA-approved study package includes the following:
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