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Hello experts,

Are HT APs required to send HT IEs in all probe responses (Probe requests from HT STA and non-HT STA)?
or
Are HT APs required to send HT IEs only when the HT STA includes HT IE in the Probe request?

I tried to google and search 11n standard but could not find this info.

Thanks

I have no idea but sound like you are studying for the CWAP lol

The short answer is yes. 802.11n capable stations must include these elements.

802.11-2007, 7.2.3 (Management Frames) "The frame body consists of the fields followed by the information elements defined for each management frame subtype. All fields and information elements [b]are mandatory[/b] unless stated otherwise and appear in the specified, relative order. STAs that encounter an element ID they do not recognize in the frame body of a received management frame ignore that element and continue to parse the remainder of the management frame body (if any) for additional information elements with recognizable element IDs."

Inclusion of the HT Capabilities and HT Operation elements (as well as a few other HT elements) [b]are conditional[/b] upon the setting of the MIB attribute "dot11HighThroughputOptionImplemented". If this attribute is true (the station is HT capable), the HT elements are included. (See 7.2.3.9 of 802.11n-2009 as well as page 371 for a brief description of the dot11... MIB attribute)

In practice, I'm sure that vendors could choose to omit these elements if the AP is configured in a non-802.11n mode.

Sean, it would be good to be already studying but that's work related. ;o)

Marcus, thanks for your answer. I want to be sure about my interpretation given that the AP is configured for b/g/n or a/n:
1) Must a non-AP HT STA include HT IEs in all probe requests?

2) If non-AP HT STA does not include HT IEs in the probe request must the HT AP include HT IEs in the probe response?

3) Must the HT AP include HT IEs in probe responses even when the STA is not HT capable?

All answers are according to the spec.

1) The HT Capabilities element, yes

2) Yes, it must (and should). But as always, implementations are proprietary, so if there are no HT fields in the request, the AP might omit them in the response.

3) Yes, HT element inclusion [u]should[/u] depend only on the AP's capabilities and not on the client's capabilities

Remember that information fields and elements listed for each management frame subtype are considered mandatory unless a specific condition exists. In this case, the condition is 802.11n support, so HT STAs should include all specified 802.11n elements. See the frame body components of management frames in 802.11 (-2007 and 802.11n), Clause 7.2.3.