- Communication with an
Access Point:
- A user node (device) can
only communicate
with an Access Point after:
- Authenication and
- Association
(E.g.: your laptop will not work on the MathCS wireless network without the correct pass code)
- A user node (device) can
only communicate
with an Access Point after:
- Authentication:
- 802.11 authentication
is the first step in
network attachment.
- 802.11 authentication requires a mobile device (station) to establish its identity with an Access Point (AP)
- 802.11 authentication
is the first step in
network attachment.
- Authentication Procedure:
- A node transmits its
- MAC address (= identity)
- Pass phrase
to an Access Point (AP) (or broadband wireless router):
- The node
can use one of the secure protocols to
send its
authentication information:
- Wired Equivanlent Privacy (WEP),
- Wi-Fi Protected Access (WPA) or
- Wi-Fi Protected Access 2 (WPA2)
(Encryption methods is outside the scope of this course)....
- A node transmits its
- Association:
- Once
authentication is
complete:
- Mobile devices can associate (register) with an AP/router to gain full access to the network.
- Association allows the
AP/router to
record
each mobile device
so that frames
may be properly delivered.
- Association only occurs on wireless infrastructure networks
- Association does not happen in ad hoc (peer-peer) mode.
- A station can only associate with one AP/router at a time.
Detailed explanation:
- The Access Point is usually
connected to the Internet
- If
a wireless node wants to
send data to
nodes on the Internet:
- the node must first associate with an Access Point.
- An Access Point will reserve buffers (= precious resource) only for associated nodes !!!
- Once
authentication is
complete:
- Association Prcedure:
- The node sends an
Asscoiation request
to the AP
- When an AP/router
grants association,
the AP will
responds with
- The status code of 0 (successful)
- The Association ID (AID).
The Association ID is used to identify the station for delivery of buffered frames
- Data frame from the Internet must be buffered at the Access Point before the Access Point can deliver the frames !!!
- The node sends an
Asscoiation request
to the AP
- Mobile nodes and
signal quality:
- Mobile nodes can
move outside the
coverage area of
an Access Point:
Result:
- The mobile node must switch to another Access Point that can provide connection with a stronger signal strength
- Mobile nodes can
move outside the
coverage area of
an Access Point:
- Switching Access Points:
- The 802.11 protocol allows
moible nodes to
switch
Access Points using a
- Hand off protocol
- The 802.11 protocol allows
moible nodes to
switch
Access Points using a
- There are 2
hand off protocols defined in
IEEE 802.11:
- Active Scanning
- Passive Scanning