Cisco Cisco Aironet 1522 Lightweight Outdoor Mesh Access Point 디자인 가이드
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Cisco Mesh Access Points, Design and Deployment Guide, Release 7.0
OL-21848-01
Connecting the Cisco 1520 Series Mesh Access Point to Your Network
QoS and DSCP Marking
Cisco supports 802.11e on the local access and on the backhaul. Mesh access points prioritize user traffic
based on classification, and therefore all user traffic is treated on a best-effort basis.
based on classification, and therefore all user traffic is treated on a best-effort basis.
Resources available to users of the mesh vary, according to the location within the mesh, and a
configuration that provides a bandwidth limitation in one point of the network can result in an
oversubscription in other parts of the network.
configuration that provides a bandwidth limitation in one point of the network can result in an
oversubscription in other parts of the network.
Similarly, limiting clients on their percentage of RF is not suitable for mesh clients. The limiting
resource is not the client WLAN, but the resources available on the mesh backhaul.
resource is not the client WLAN, but the resources available on the mesh backhaul.
Similar to wired Ethernet networks, 802.11 WLANs employ Carrier Sense Multiple Access (CSMA),
but instead of using collision detection (CD), WLANs use collision avoidance (CA). This means that
instead of each station trying to transmit as soon as the medium is free, WLAN devices will use a
collision avoidance mechanism to prevent multiple stations from transmitting at the same time.
but instead of using collision detection (CD), WLANs use collision avoidance (CA). This means that
instead of each station trying to transmit as soon as the medium is free, WLAN devices will use a
collision avoidance mechanism to prevent multiple stations from transmitting at the same time.
The collision avoidance mechanism uses two values, called CWmin and CWmax. CW stands for
contention window. The CW determines what additional amount of time an endpoint should wait, after
the interframe space (IFS), to attend to transmit a packet. Enhanced distributed coordination function
(EDCF) is a model that allows end devices that have delay-sensitive multi-media traffic to modify their
CWmin and CWmax values to allow for statically greater (and more frequent) access to the medium.
contention window. The CW determines what additional amount of time an endpoint should wait, after
the interframe space (IFS), to attend to transmit a packet. Enhanced distributed coordination function
(EDCF) is a model that allows end devices that have delay-sensitive multi-media traffic to modify their
CWmin and CWmax values to allow for statically greater (and more frequent) access to the medium.
Cisco access points support EDCF-like QoS. This provides up to eight queues for QoS.
These queues can be allocated in several different ways, as follows:
•
Based on TOS / DiffServ settings of packets
•
Based on Layer 2 or Layer 3 access lists
•
Based on VLAN
•
Based on dynamic registration of devices (IP phones)
AP1520s, in conjunction with Cisco controllers, provides a minimal integrated services capability at the
controller, in which client streams have maximum bandwidth caps, and a more robust differentiated
services (diffServ) capability based on the IP DSCP values and QoS WLAN overrides.
controller, in which client streams have maximum bandwidth caps, and a more robust differentiated
services (diffServ) capability based on the IP DSCP values and QoS WLAN overrides.
When the queue capacity has been reached, additional frames are dropped (tail drop).
Encapsulations
There are several encapsulations used by the mesh system. These include CAPWAP control and data
between the controller and RAP, over the mesh backhaul, and between the mesh access point and its
client(s). The encapsulation of bridging traffic (non-controller traffic from a LAN) over the backhaul is
the same as the encapsulation of CAPWAP data.
between the controller and RAP, over the mesh backhaul, and between the mesh access point and its
client(s). The encapsulation of bridging traffic (non-controller traffic from a LAN) over the backhaul is
the same as the encapsulation of CAPWAP data.
There are two encapsulations between the controller and the RAP. The first is for CAPWAP control, and
the second for CAPWAP data. In the control instance, CAPWAP is used as a container for control
information and directives. In the instance of CAPWAP data, the entire packet, including the Ethernet
and IP headers, is sent in the CAPWAP container (see
the second for CAPWAP data. In the control instance, CAPWAP is used as a container for control
information and directives. In the instance of CAPWAP data, the entire packet, including the Ethernet
and IP headers, is sent in the CAPWAP container (see
).