Last Post: January 17, 2005:
The first paragraph of page 70 of the CWNA Study Guide indicates that the FCC defines 26 standard hop patterns for FHSS systems. On-line practice Test C contains a question whose answer indicates the IEEE defines 22 FHSS channels (hop patterns). I don't see any mention in the CWNA Study Guide about hop patterns defined by the IEEE.
Do both the FCC and IEEE define FHSS hop patterns? Are the 22 hop patterns defined by the IEEE a subset of the 26 defined by the FCC?
I suggest the following changes to the CWNA study guide regarding FHSS. Please let me know if you find them helpful or needing improvement.
page 68 after Figure 3.2, first paragraph second sentence ==> Reword: Ã¢Â€ÂœThe process of repeating the sequence will continue indefinitely.Ã¢Â€Â
page 68 next to last paragraph first sentence ==> Reword: Ã¢Â€ÂœAll radios within a basic service set use the hop sequence announced in beacons in order to send and receive on the proper frequency at the proper time.Ã¢Â€Â
page 69 first paragraph last sentence ==> Reword: Ã¢Â€ÂœThe rest of the spread spectrum signal would remain intact, and the lost data may be retransmitted on another frequency.Ã¢Â€Â
page 70 figure 3.3 ==> The three blocks at the bottom should be labeled Ã¢Â€ÂœBSS Using Sequence 1Ã¢Â€Â Ã¢Â€ÂœBSS Using Sequence 2Ã¢Â€Â and Ã¢Â€ÂœBSS Using Sequence 3Ã¢Â€Â. Also the graphic should show that each BSS hops at a difference moment of time rather than all at the same time.
page 70 all three paragraphs including the top of page 71 ==> Reword: Ã¢Â€ÂœAll the stations of a frequency hopping BSS operate using a specified hop pattern, also called a hopping sequence. Frequency hopping stations typically use one of the FCCÃ¢Â€Â™s three hop sets. Each set has twenty-six hop patterns for a total of seventy-eight unique hop patterns, numbered 0-77. Each hop pattern specifies a different arrangement of the same seventy-nine 1 MHz frequency channels ordered such that each hop is at least six MHz up or down the frequency band. The channels within any one hop pattern are identified by hop index, numbered 1-79. Some frequency hopping stations will allow custom hop patterns to be created.
All stations in a frequency hopping BSS synchronize by agreeing on current hop set, current hop pattern, and current hop index. When it is time to hop, each station increments its hop index, wrapping to zero if necessary, and calculates which frequency channel to use next.
Some frequency hopping equipment vendors allow synchronization between multiple BSSÃ¢Â€Â™s all using the same hop set and hop pattern but starting at a different hop index and hopping to the next channel at the same moment. In this way it is theoretically possible to have as many as seventy-nine synchronized co-located BSSÃ¢Â€Â™s that never operate on the same channel at the same time. The cost of such a system is prohibitive and is generally not considered an option. In practice no more than 12 such co-located BSSÃ¢Â€Â™s is considered practical.
If non-synchronized BSSÃ¢Â€Â™s are to be used, depending on traffic, an upper limit of fifteen to twenty-six co-located frequency hopping BSSÃ¢Â€Â™s may be used with acceptable interference. As more co-located BSSÃ¢Â€Â™s and/or traffic are added to this environment multiple BSSÃ¢Â€Â™s operate on the same channel at the same time while other channels go unused placing an upper limit on aggregate throughput.Ã¢Â€Â
I am going through the practice exams and also found the same inconsistancy (22 freq hopping patterns or 26?). My question is simple. What will the correct answer be for the CWNA exam? (22 or 26?). I would like to know so I can correct my Official Study Guide if it is incorrect.
IEEE states, according to IEEE P802.11-96/49D:
78 hopping patterns organized in 3 sets of 26 patterns each.