IEEE 802.11 Handbook, Additional Material

Additional Material for the
IEEE 802.11 Handbook

This page will be kept updated with the most recent corrections and additional material for the Handbook. The authors will also post answers that bring new information to light from questions that are received at handbook@informed-technology.com.

Additional Material

There is a list of acronyms that was not included in the book.

Page 31: The implication of changes made to the MAC when the 802.11b PHY (higher rate extension to DSSS) was adopted are not clearly spelled out in the standard. 802.11b states that the PHY is to be considered both a direct sequence and a frequency hopping PHY. This was included to make it possible for the 802.11b PHY to operate cooperatively with older FH systems. The changes to the MAC were very small. A restriction on when the FH and DS information elements are to be used was removed. This change now allows both of these elements to be included in the Beacon and Probe Response frames sent by an 802.11b AP. Stations that are compliant with 802.11b now are able to participate in a fully isochronous CFP. This comes about because of the existing requirement that the MAC not begin a transmission that can not be completed, including the ACK from the destination, before the current FH dwell time expires. Thus, an 802.11b AP can significantly increase the probability that it will be able to begin the CFP exactly at the TBTT.

Page 63: The standard does not clearly indicate the setting and meaning of the Privacy bit in the Capabilities Information Field for all cases. In section 7.3.1.4 of the standard, the use by the AP is described and the use by a station in an IBSS is described. However, there is no mention of how a station in an infrastructure network is to use this bit. The current consensus is that a station will set this bit in its association request frame if WEP is enabled. The implications of the use of this bit by the AP are that the AP may refuse an association request from a station where the Privacy bit in the station's CIF is zero and the AP's Privacy bit is one. Similarly, a station will not attempt to associate with an AP when the AP's Privacy bit is zero and the station's Privacy bit is one. These actions will ensure that the data traffic in a BSS is either entirely in the clear (unencrypted) or entirely encrypted. There will be no BSSs where there is a mix of clear and encrypted data traffic.

Errata and Other Corrections

Page 31: In Figure 3-4, the third block should hold the text "Data+CF-Ack+CF-Poll to Station 2". There should also be an ellipsis ("...") before the block holding the text "CF-End" to indicate that there are other frames in the CFP that occur before the CFP is ended.

Page 60: At the end of the first line in the "Capability Information" section, the word "the" should be "that". Also, the word "qssaciation" in the middle of the page should be "association".

Page 116: In Figure 6-3, the CRC at the end of the PLCP header should be 16 bits, not 8.

Page 133: In Figure 6-11, the CRC at the end of the PLCP header should be 16 bits, not 8.

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