In my last post I only introduced myself, and the CCNA Wireless Certification. In this post I want to lay the groundwork regarding some of the terminology used in Wireless Networking. Lets begin with the ISM bands. ISM is an Acronym that stands for Industry, Scientific, and Medical. The ISM bands are defined by the ITU-R. The folks at the ITU-R set Radio Regulations. These bands are typically intended for unlicensed use. That means anyone can use them. Your Access-Points operate in the ISM bands. This brings us to the 802.11a/b/g/n standards. The 2.4-GHz ISM band ranges from 2.4 to 2.4835 GHz (2.4970 GHz in Japan). This is the range used by 802.11b, 802.11g. The 5-GHz ISM band ranges from 5.725 to 5.875 GHz. What is unique about the 5-GHz ISM band is that it actually overlaps with the Unlicensed National Information Infrastructure (UNII) bands:
- –UNII-1 which ranges from 5.15 to 5.25 GHz.
- –UNII-2 ranges from 5.25 to 5.35 GHz.
- –UNII-2 extended ranges from 5.470 to 5.725 GHz.
- –UNII-3 ranges from 5.725 GHz to 5.825 GHz.
Using these frequency ranges can carry extra requirements that I wont discuss here, but its something that you need to know if you pursue the CCNA Wireless. The 5-GHz ISM rages is used by the 802.11a standard. The 802.11n standard operates in the 2.4-GHz, the 5-GHz radio band, or both bands, offering backward compatibility with preexisting 802.11a/b/g deployments. Wireless solutions based on the 802.11n standard employ several techniques to improve the throughput, reliability, and predictability of wireless LANs. The three primary innovations are:
- -Multiple Input Multiple Output (MIMO) technology
- -Packet aggregation
- -Channel bonding (40MHz Channels)
Together, these techniques allow 802.11n solutions to achieve up to nine times the performance over current 802.11a/b/g networks. The following chart displays a nice summary of these protocols, the data rates they are capable of, and frequency range they operate in. The chart also displays the method of transmission that they use. 802.11b uses Direct Sequence Spread Spectrum (DSSS) while 802.11a uses Orthogonal Frequency Division Multiplexing (OFDM). 802.11g and n use OFDM. Last but not least I want to mention this post in no way covers everything. There are however a few resources that I want to make you aware of. First off there is a great deal of information on the Cisco Learning Network specifically regarding the CCNA Wireless Exam and the topics covered therein. Another great resource is the Cisco Wireless Section of their Web site. And of course you can find more information on the CCNA Wireless topics as well as practice questions in the book CCNA Wireless Official Exam Certification Guide. I personally use my Cisco Press Safari Account to get access to all the Cisco Press books in a searchable format. And a final note, I mentioned some free Webinars that I will be doing this month. You can register for the first one, CCNA Wireless Technical Introduction by clicking on this link. The session will be held February 11th at 11:30am PST. Based on your feed back future sessions may be held at different times. Hope you enjoy and look forward to speaking to you in the Webinar.
