function to signal condition information to ensure that the ephemeral nature of RF environments does not
impact network stability.
Traffic Flow
The traffic flow within the wireless mesh can be divided into three components:
1
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.
2
Wireless mesh data frame flow.
3
AWPP exchanges.
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 18: Wireless Mesh Frame, on page 43
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 18: Wireless Mesh Frame
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
Cisco Mesh Access Points, Design and Deployment Guide, Release 7.3
OL-27593-01
43
Mesh Network Components
Adaptive Wireless Path Protocol