The traffic flow within the
wireless mesh can be divided into three components:
Overlay CAPWAP traffic that
flows within a standard CAPWAP access point deployment; that is, CAPWAP traffic
between the CAPWAP access point and the CAPWAP controller.
Wireless mesh data frame
As the CAPWAP model is well
known and the AWPP is a proprietary protocol, only the wireless mesh data flow
is described. The key to the wireless mesh data flow is the address fields of
the 802.11 frames being sent between mesh access points.
An 802.11 data frame can use
up to four address fields: receiver, transmitter, destination, and source. The
standard frame from a WLAN client to an AP uses only three of these address
fields because the transmitter address and the source address are the same.
However, in a WLAN bridging network, all four address fields are used because
the source of the frame might not be the transmitter of the frame, because the
frame might have been generated by a device
behind the transmitter.
Figure 1 shows an
example of this type of framing. The source address of the frame is MAP:03:70,
the destination address of this frame is the controller (the mesh network is
operating in Layer 2 mode), the transmitter address is MAP:D5:60, and the
receiver address is RAP:03:40.
Figure 4. Wireless Mesh
As this frame is sent, the
transmitter and receiver addresses change on a hop-by-hop basis. AWPP is used
to determine the receiver address at each hop. The transmitter address is known
because it is the current mesh access point. The source and destination
addresses are the same over the entire path.
If the RAP’s controller
connection is Layer 3, the destination address for the frame is the default
gateway MAC address, because the MAP has already encapsulated the CAPWAP in the
IP packet to send it to the controller, and is using the standard IP behavior
of using ARP to find the MAC address of the default gateway.
Each mesh access point within
the mesh forms an CAPWAP session with a controller. WLAN traffic is
encapsulated inside CAPWAP and is mapped to a VLAN interface on the controller.
Bridged Ethernet traffic can be passed from each Ethernet interface on the mesh
network and does not have to be mapped to an interface on the controller (see
Figure 5. Logical Bridge and WLAN