《IEEE802.11-2012 Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications 》
8. Frame formats
8.4 Management frame body components
8.4.2 Information elements
8.4.2.10 Country element
The Country element contains the information required to allow a STA to identify the regulatory domain in
which the STA is located and to configure its PHY for operation in that regulatory domain.
The format of this element is as shown in Figure 8-90.
The element ID for this element is set to the value for Country, specified in Table 8-54. The length of the
element is variable, as the element may contain more than one triplet comprising the First Channel Number,
Number of Channels, and Maximum Transmit Power Level fields and referred to as subband triplets.
Alternatively, where dot11OperatingClassesRequired is true and the First Channel Number/Operating
Extension Identifier octet has a positive integer value of 201 or greater, then that triplet comprises the
Operating Extension Identifier, Operating Class, and Coverage Class fields. Together they are referred to as
an operating triplet. The minimum length of the element is 8 octets.
The Country String field of the element is 3 octets in length. The AP and mesh STA set this field to the value
contained in the dot11CountryString attribute before transmission in a Beacon or Probe Response frame.
Upon reception of this element, a STA sets the value of the dot11CountryString to the value contained in
this field.
The First Channel Number/Operating Extension Identifier field is 1 octet in length. If the field has a positive
integer value less than 201, then it contains a positive integer value that indicates the lowest channel number
in the subband described in this element. The group of channels described by each pair of the First Channel
Number and the Number of Channels fields do not have overlapping channel identifiers. [For example, the
pairs (2,4) and (5,2) overlap and are not used together.] The First Channel Numbers are monotonically
increasing where dot11OperatingClassesRequired is not true.
Where dot11OperatingClassesRequired is true, consecutive subband triplets following an operating triplet
have monotonically increasing First Channel Number fields.
The Number of Channels field of the subelement is 1 octet in length.
ISO/IEC 3166-1, Codes for the representation of names of countries and their subdivisions—Part 1: Country
codes.