Cisco aironet 1522 Design And Deployment Manual page 109

All backhaul frames are treated identically, regardless of whether they are MAP to MAP, RAP to MAP,
or MAP to RAP.
Figure 70
Mesh
Header
Mesh
Header
Queuing on the Mesh Access Point
The mesh access point uses a high speed CPU to process ingress frames, Ethernet, and wireless on a
first-come first-serve basis. These are queued for transmission to the appropriate output device, either
Ethernet or wireless. Egress frames can be destined for either the 802.11 client network, the 802.11
backhaul network, or Ethernet.
AP1520s support four FIFOs for wireless client transmissions. These FIFOs correspond to the 802.11e
platinum, gold, silver, and bronze queues, and obey the 802.11e transmission rules for those queues. The
FIFOs have a user configurable queue depth.
Likewise, the backhaul (frames destined for another outdoor mesh access point) uses four FIFOs, though
user traffic is limited to gold, silver, and bronze. The platinum queue is used exclusively for CAPWAP
control traffic and Voice, and has been reworked from the standard 802.11e parameters for CWmin,
CWmax, and so on, to provide more robust transmission but higher latencies.
Similarly, the 802.11e parameters for CWmin, CWmax, and so on, for the gold queue have been
reworked to provide lower latency at the expense of slightly higher error rate and aggressiveness. The
purpose of these changes is to provide a channel more conducive to video applications.
Frames destined for Ethernet are queued as FIFO, up to the maximum available transmit buffer pool (256
frames). There is a support for Layer 3 IP Differentiated Services Code Point (DSCP), so marking of the
packets is there as well.
In the controller to RAP path for the data traffic, the outer DSCP value is set to the DSCP value of the
incoming IP frame. If the interface is in tagged mode, the controller sets the 802.1Q VLAN ID, and
derives the 802.1p UP (outer) from 802.1p UP incoming and the WLAN default priority ceiling. Frames
with VLAN ID 0 are not tagged (See
Cisco Aironet 1520, 1130, 1240 Series Wireless Mesh Access Points, Design and Deployment Guide, Release 6.0
OL-20213-01
Encapsulating Mesh Traffic
RAP
Bridging Packet
802.1/802.1P IP/IP DSCP
Figure
Connecting the Cisco 1520 Series Mesh Access Point to Your Network
MAP
CAPWAP
CAPWAP Control/Data
Encapsulation
71).
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