Last Post: January 16, 2012:
Country element (ID = 7) has 4 data fields:
Country String (3B)
First Channel Number / Operating Extension Identifier (1B)
Number of Channels / Operating Class (1B)
Maximum Transmit Power Level / Coverage Class (1B)
When the last three data fields are repeated, as determined by the Length field
(Source: 802.11 standard, Country element format)
Does anyone knows when the data refers to the triplet (First Channel Number, Number of Channels, Maximum Transmit Power Level) and when to the other triplet (Operating Extension Identifier, Operating Class, Coverage Class)?
My goal is to parse the Operating Class, and thats the only element i have found it in.
Wouldn't that be an either/or case? I mean, if you are using let's say 802.11g, then the channel spacing is defined for that PHY.
If the operating class defines the channel spacing, then it would be constant for that particular PHY.
I think that value would be the number of channels, unless some other bit is set which changes the meaning of this element. I can't find further info on this in the CWAP book, but now I want to know too!
What is your overall goal? (I mean, why do you want to parse the operating class?)
First - thanks.
My goal is to write 20/40 Coexistence for STA, so i need to fill an INTOLERANT_CHANNELS_REPORT for the COEXISTENCE_FRAME, and this field is needed (it's source is the beacons which the STA collects and from what i have found it appears in the channel element).
I've used a sniffer and it parse the element and shows the first triplet (apparently since the first octet is 1)
i've found a document ([url=http://www.google.co.il/url?sa=t&rct=j&q=%22country+element%22+%22operating+class%22&source=web&cd=1&ved=0CB8QFjAA&url=https%3A%2F%2Fmentor.ieee.org%2F802.11%2Fdcn%2F10%2F11-10-0514-00-00af-channel-power-map.doc&ei=zcYOT-7TAYqI4gTPoZyLBA&usg=AFQjCNEZjOWi35K8Uikupb1F0p31mUUAKg]Document URL[/url]) from which one can learn that if the First Channel Number / Operating Extension Identifier field is 201 then the next field is referenced as operating class and not as channel number.
So your thinking have a good direction as it appears by that document :)
But, what about this information (operating class) when it does not appear in this element?
How will i know the operating class of the beacon??
please also view this document ([url=http://www.google.co.il/url?sa=t&rct=j&q=%22country+element%22+%22operating+class%22&source=web&cd=2&ved=0CCUQFjAB&url=https%3A%2F%2Fmentor.ieee.org%2F802.11%2Fdcn%2F11%2F11-11-0306-00-00ac-comment-resolution-tpc.doc&ei=zcYOT-7TAYqI4gTPoZyLBA&usg=AFQjCNH_YMAZ5XD-PPsFjtZr6FZEAKG11g]Document URL[/url])
I would have thought you'd only have to worry about that if you're programming the AP. (I assume you're talking about programming).
In the AP, in the HT operation element, there are the following values:
0 No secondary channel, meaning 20MHz BSS
1 Secondary channel is above primary
3 Secondary channel is below primary.
If the STA uses 20MHz, the AP will communicate with it on the primary channel. (which you probably are already well aware of). If the STA uses 40MHz, then the AP will communicate accordingly. These parameters are established on assocation.
I may have completely missed something here though, but maybe the information you're looking for can be found elsewhere in management frames.
I do recall somewhere in the depths of the standards that even in a BSS, two stations can directly communicate with each other in a certain way (not talking about IBSS here), but no-one implements it. (I'm sure I read that somewhere along the way) I guess in that case if one STA were 40MHz and the other 20MHz then something would have to be done. Just an idea.
That's correct but does not relate to what i'm looking for.
i tried hard to find it in other management frames, and found one, but it's optional to send it, so i really don't understand where can one get this info any time, and not just in some cases.
maybe i should refer to all relevant operating classes for the given channel??
In the early days of IEEE 802.11, the system was set up such that only a few regulatory domains were recognized. What is a regulatory domain ? In a country such as the United States, Government control of frequency spectrum is an absolute requirement. We can imagine the chaos that would occur if private companies and individuals had to control allocation of frequency space and power levels. Each company would have it?s own best interests in mind, and it would be very difficult to get anything done in terms of finalizing rules and regulations.
In the US, the FCC ( Federal Communications Commission ) is the branch of the US Government that is responsible for allocating and regulating power and bandwidth ( and other related parameters ). The FCC listens to various companies objections and/or support for proposed spectrum changes, but it has the final say. Some of the issues can be complex and costly:
They deal with two basic entities:
1. Licenced spectrum, such as in relation to cellular phone calls, in which a company may pay for the exclusive right to ?own? a portion of the RF spectrum. If interference occurs, the buyer or licence operator has the right to complain to the FCC, who in turn, will do their best to work with the customer to resolve the issue.
2. Unlicenced spectrum, such as Wi-Fi. In this case, users do not need to obtain a licence to operate, in for example, the 2.4 GHz band. If someone experiences interference, then usually it?s just a matter of ?well, that?s the name of the game here?.
In both cases, however, there are certain regulatory parameters that must be obeyed, even in an unlicenced band. For example, there are restrictions on absolute ( physical power ) and antenna gain. If an unlicenced operator supects that interference is coming from another unlicenced operator who has ?gone over? the regulatory power limits ( too high an antenna gain for example ), then there is the possibility of the FCC becoming involved. This is rare however.
The FCC has many functions, but some of the most important are to create rules and regulations which will help minimize the interfering effects of one network on another ( even to some degree in the unlicenced band ).
There are many scientific and military organizations who share the unlicenced bands. Wi-Fi networks need to take this into consideration at times. For example, many of us are familiar with the concept of Dynamic Frequency Selection, whereby a Wi-Fi network may have to take ?avoiding action? if radar pulses ( or energy reported as being of radar origin ) are detected in areas such as the UNII 2 and UNII 2e bands in the 5 GHz spectrum.
Now, it so happens that different countries may have different services present in the Wi-Fi bands compared with others. For example, one country may have scientific usage of certain portions of the bands, whereas other countries may not. What is applicable to the RF environment in the US, may not necessarily be applicable to another country. In general, each country has it?s own regulatory agency.
In some areas, there are strong cultural, business and military connections between countries. In some of these cases, the countries may get together and form a regulatory agency that applies similar rules to all members. For example, in Europe, an organization called ETSI ( European Tecommunications Standards Institute ) sets regulations for RF spectrum usage which applies to a large number of European neighbors.
A regulatory domain is simply a geographical area ( for example the US ) that is covered by rules relevant to that area. Again, in the regulatory domain of the US, the entity responsible, is the FCC.
When 802.11 first started up, the regulations that were created in the IEEE docs to specify compliance, covered certain countries ( who had been working on the creation of the specs ) such as the US, Canada and Japan.
It was soon realised that Wi-Fi was taking off world-wide. An access point meant for the US could end up in another country where the local regulations were entirely different. This could have led to all sorts of legal problems with interference etc. It may also mean that that particulary country could ban the import of such devices. Certification of the devices by the appropriate body, prior to import in that country, was the answer.
In order to help get around this, manufacturers worked in cooperation with the IEEE. One particular method would be to program a table of regulatory domain information such as country name with appropriate values of power and frequency etc. The problem with this is that regulatory changes may take place. Therefore, the devices would have to be capable of for example, firmware changes to update the table.
In actual practice, regulatory changes such as those mentioned are rare.
The next idea to come up was to simply have the AP and STA advertise the regulatory domain that they were to operate in. Most governments have groups that control the import of such devices.
Information Elements ( or IEs ) are frames which are included in such things as beacons, and advertise certain information which is useful for the STAs. For example, in FT, a MDIE ( Mobility Domain Information Element ) is sent in certain frames. This element contains the ?name?of a mobility domain which can prove useful to STAs which wish to roam. There are all sorts of IEs ( lists can be found in e.g. IEEE 802.11-2007 etc ).
The idea now was that an AP could advertise regulatory information by means of the newly created Country Information Element. This element would basically say ?Hey, I?m an AP from Japan ( say ) , if anyone wants to communicate with me, you have to show me that you have been programmed with the correct regulatory information by means of entering in a country code by means of your device?s configuration method. If you cannot show this to me, I won?t allow you to connect?sorry?.
If a US manufacturer wishes to export some new APs etc into Japan, they cannot simply put them on a boat and send them off. Tests have to be done to prove to the regulatory agency ( in Japan in this case ), that the device will be within the regulatory specification s of that country. Certificates are awarded upon successful completion of testing.
Military organizations may use certain frequencies that are not publically known. This can sometimes be a reason why there may be problems with certification etc.
You are correct. The arrangement is known as a Direct Link Setup or DLS. Details may be found in Section 11.7 of the IEEE 802.11 ? 2007 document.
It was originally part of the IEEE 802.11e spec. That also included work on security. When WEP vulnerabilities were first shown, a split-off task group 802.11i was quickly formed to deal with that.
In Australia the authority is Australian Communications and Media Authority (ACMA). (This ACMA not to be confused with Aruba's ACMA certification)
Trying to get the technical info required from the website is a nightmare though.
To be honest, Australia generally tends to just copy other countries like US or Europe, although we don't have a big problem from neighbouring countries, given that it's an island :)
You are right. In the first triplet ( grouping of octets ) following the Country Strings, if the value of the first octet is less than 201, the second group of triplets refers to the ?traditional? IEEE 802.1d system of ?First Channel Number/Number of Channels/Maximum Transmit Power Level?. However, if the value of the first octet is 201 or greater, we now shift to the meaning of ?Regulatory Extension Identifier/Regulatory Class/Coverage Class? ( this was not present in the original IEEE 802.11d spec ).
Very often we find that there are different terms used by different organizations/manufacturers in Wi-Fi. I would suggest that you always use the terms indicated in the IEEE docs. This is not nit picking. There are some good reasons behind this.
"Operating Class" . IEEE refers to this as "Regulatory Class"
"Operating Extension Identifier". IEEE refers to this as "Regulatory Extension Identifier"
Now, using the term ?Regulatory Class?, we can find that Annex I ( Regulatory Classes ) of the IEEE 2001-2007 spec gives us some useful information, as does Annex J ( Country Information and Regulatory Classes ).
Bye the way, when looking at Maximum Transmit Power Level values, be careful. Some regulatory authorities refer to the value as the value at the input to the antenna connector. Others effectively refer to EIRP values, by giving the power at boresight from the output of the antenna. If in doubt, refer to the regulatory documents of the country of interest.
Ah, I figured there must be something that defines when the different meanings are in effect. Well done.