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= 802.11 Reference Design Experiments Framework Basic Service Set (BSS) =

The 802.11 Reference design uses a structure to record information about a [https://en.wikipedia.org/wiki/Service_set_(802.11_network) basic service set (BSS)].  This information can be for the node's current BSS (i.e. network) or networks that the node has seen by either receiving a beacon or from [http://warpproject.org/docs/mango-wlan-exp-dev/node.html#network-scan scanning for networks].  Each node is either a member of no BSS (colloquially "unassociated") or a member of one BSS.  The following fields are recorded in the BSS information structure to describe a BSS:

||=  Field Name  =||=  Description  =||
|| bssid || BSS ID ||
|| channel || Primary channel ||
|| channel_type || Channel Type ||
|| latest_beacon_rx_time || Value of System Time in microseconds of last beacon Rx ||
|| ssid || SSID (32 chars max) ||
|| latest_beacon_rx_power || Last observed Rx Power (dBm) ||
|| flags || BSS flags ||
|| capabilities || Supported capabilities of the BSS ||
|| beacon_interval || Beacon interval - In time units of 1024 us ||


=== Python ===

The 802.11 Reference Design Experiments Framework provides methods to interact with BSS information.  In addition to the fields above, the BSS information structures in Python also contain a {{{timestamp}}} field which is the value of the MAC time in microseconds when the structure was created.  The following methods are used to interact with BSS information:

  * [http://warpproject.org/docs/mango-wlan-exp-dev/node.html#wlan_exp.node.WlanExpNode.get_bss_info get_bss_info()]

     This method will return the BSS information about the node's current BSS.  The value returned can be {{{None}}} if the node is not a member of a BSS.

  * [http://warpproject.org/docs/mango-wlan-exp-dev/node.html#wlan_exp.node.WlanExpNode.get_network_list get_network_list()]

    This method will return a list of BSS information about all the networks that the node has seen.  This list can include the node's current BSS if the node is a member of a BSS.  This list could be empty.

  * '''{{{configure_bss()}}}''' for [http://warpproject.org/docs/mango-wlan-exp-dev/node_ap.html#wlan_exp.node_ap.WlanExpNodeAp.configure_bss AP], for [http://warpproject.org/docs/mango-wlan-exp-dev/node_sta.html#wlan_exp.node_sta.WlanExpNodeSta.configure_bss STA], for [http://warpproject.org/docs/mango-wlan-exp-dev/node_ibss.html#wlan_exp.node_ibss.WlanExpNodeIBSS.configure_bss IBSS]
      
    This method will configure the node's current BSS.  For each node type, there is a specific implementation of {{{configure_bss}}} that has different argument requirements.  See below for more details.



=== Configuring the BSS ===

A node requires a minimum set of information to be a member of a BSS. The minimum set of information is:
   * BSSID: 48-bit MAC address
   * Channel: logical channel for Tx/Rx by BSS members
   * SSID: variable length string
   * Beacon Interval: time between TBTTs in units of TUs (not required by STA)

A node's current BSS can be populated by default in C, by active scanning, or by wlan_exp.  The DIP switch on the WARP v3 node can be used to control the default BSS at boot (see [http://warpproject.org/trac/wiki/802.11/Usage/UserIO user I/O documentation] for each MAC project).

'''Arguments:'''

 * {{{bssid}}}: depends on node type; {{{None}}} means wipe BSS state; {{{False}}} means no change
  * '''AP''': must be node's wireless MAC address
  * '''STA''': must be BSSID of BSS with which to associate
  * '''IBSS''': must be valid locally-administered BSSID (use [http://warpproject.org/docs/mango-wlan-exp-dev/wlan_exp_util.html#wlan_exp.util.create_locally_administered_bssid create_locally_administered_bssid()] utility to create locally-administered BSSIDs from MAC addresses)
 * {{{ssid}}}: string; {{{None}}} means no change
 * {{{beacon_interval}}}: integer in ![10, 65534]; {{{None}}} means no beacon Tx; {{{False}}} means no change
 * {{{channel}}}: Integer channel index; {{{None}}} means no change
 * {{{ht_capable}}}: Does the node advertise HT processing capabilities; {{{None}}} means no change

=== Changes to code from 802.11 Reference Design v1.4 ===

  * '''Replaces:'''
    * {{{node.set_channel()}}}: New method [http://warpproject.org/docs/mango-wlan-exp-dev/node.html#wlan_exp.node.WlanExpNode.set_radio_channel set_radio_channel()] only affects hardware, not BSS
    * {{{node_ap.get/set_ssid()}}}: Use {{{get_bss_info()}}} as getter
    * {{{node_ap.get/set_beacon_interval()}}}: Use {{{get_bss_info()}}} as getter
    * {{{node_sta.set_association()}}}
    * {{{node_ibss.join()}}}
    * {{{util.create_bss_info()}}}

  * '''Affected:'''
    * {{{node.reset()}}} has new arguments:
      * {{{bss=bool}}}: nullifies the node's BSS state but does not remove any entries from the BSS information list; wipes station_info list
        * {{{n.reset(bss=True)}}}, unlike {{{n.configure_bss(bssid=None)}}}, shall produce the following OTA transmission:
          * For AP, a deauthentication frame to each associated station
          * For STA, a disassociation frame to its AP
          *  For IBSS, nothing. {{{n_ibss.reset(bss=True)}}} == {{{n_ibss.configure_bss(bssid=None)}}}
      * {{{network_list=bool}}}: wipes the node's list of overheard BSS information, excluding the bss_info entry for the node's current network (if any)
      * Removed arguments {{{associations=bool}}}, {{{bss_info=bool}}}
    * {{{node.reset_all()}}} includes {{{(bss=True, network_list=True)}}}


=== Example: Configuring BSS ===


{{{#!python
# Setup a new network with 1 AP, 1 STA
#     - Assumes that both nodes started with no default BSS (i.e. 
>>> n_ap.configure_bss(ssid='My Network', beacon_interval=100, channel=6, ht_capable=True)
>>> n_ap.get_bss_info()
{'bssid': AP_WLAN_MAC_ADDR, 'ssid': 'My Network', 'beacon_interval': 100, 'channel': 6, 'ht_capable': True, ...}

>>> n_sta.get_bss_info()
None

>>> n_ap.add_association(n_sta)

>>> n_sta.get_bss_info()
{'bssid': AP_WLAN_MAC_ADDR, 'ssid': 'My Network', 'beacon_interval': 100, 'channel': 6, 'ht_capable': True, ...}

# Update the beacon interval
>>> n_ap.configure_bss(beacon_interval=250)
>>> n_ap.get_bss_info()
{'bssid': AP_WLAN_MAC_ADDR, 'ssid': 'My Network', 'beacon_interval': 250, 'channel': 6, 'ht_capable': True, ...}

# Query STA before it receives a new beacon
>>> n_sta.get_bss_info()
{'bssid': AP_WLAN_MAC_ADDR, 'ssid': 'My Network', 'beacon_interval': 100, 'channel': 6, 'ht_capable': True, ...}

# Query STA after it receives a new beacon
>>> time.sleep(250*1024*1e-6)
>>> n_sta.get_bss_info()
{'bssid': AP_WLAN_MAC_ADDR, 'ssid': 'My Network', 'beacon_interval': 250, 'channel': 6, 'ht_capable': True, ...}

# Retune both nodes by adjusting the BSS channel
for n in [n_ap, n_sta]:
    n.configure_bss(channel=7)

# Disable AP beacon Tx
>>> n_ap.configure_bss(beacon_interval=None)
}}}

=== Example:  Changing Channel ===



{{{#!python
# No command arguments, no response payload
my_node.send_user_command(CMDID_USER_MYCMD, args=None)
}}}


=== Example:  Adjusting Beacon Interval ===

{{{#!python
# No command arguments, no response payload
my_node.send_user_command(CMDID_USER_MYCMD, args=None)
}}}


=== Example:  Scanning for Networks ===

{{{#!python
# No command arguments, no response payload
my_node.send_user_command(CMDID_USER_MYCMD, args=None)
 args=[ARG0 ARG1])
}}}