Cisco Cisco 5508 Wireless Controller 기술 참조
4
Radio Resource Management–Radio Frequency Grouping Algorithm
NDP
How RF Groups are Formed
When the WLC is initialized, it creates a unique Group ID using the IP address of the WLC and a Priority
Code. The Priority Code is assigned based on the controller model and MAX license count (hardware
limit) to create a hierarchical model and ensure that the controller with the most processing capacity is
assigned the job of Group Leader (GL). The Group ID and RF Group Name will be used together in
messages to other WLCs and APs to identify them. Devices having the same RF Group Name will
interoperate as members of the same RF Group.
Code. The Priority Code is assigned based on the controller model and MAX license count (hardware
limit) to create a hierarchical model and ensure that the controller with the most processing capacity is
assigned the job of Group Leader (GL). The Group ID and RF Group Name will be used together in
messages to other WLCs and APs to identify them. Devices having the same RF Group Name will
interoperate as members of the same RF Group.
The current controller hierarchy in terms of capacity is as such:
8500 > 7500 > 5760 > WiSM2 > 5508 > vWLC > 3850 > 2500
When comparing Group IDs for leader election, the priority code is the primary criteria and the IP
address is secondary. For instance, if there are three other controllers with same priority code, the one
with the highest IP address assumes the GL role.
address is secondary. For instance, if there are three other controllers with same priority code, the one
with the highest IP address assumes the GL role.
For two WLCs to form an RF Group, there is an infrastructure as well as OTA (Over The Air) component:
•
WLCs must be reachable to one another on the distribution network.
•
They must each have at least one AP that can hear other’s NDP messages above -80 dBm.
The distribution network communicates over unicast UDP:
The OTA component relies on two functions–NDP and collection of off channel metrics. Assume that
NDP is the Off Channel TX cycle and monitoring of off channel metrics is the off channel RX cycle. In
general, both NDP and monitoring are critical to the topic of RF Grouping and RRM .
NDP is the Off Channel TX cycle and monitoring of off channel metrics is the off channel RX cycle. In
general, both NDP and monitoring are critical to the topic of RF Grouping and RRM .
NDP
One of the most unique features about Cisco’s RRM implementation is that it uses OTA messages and
operates in a centralized manner even in large deployments. This advantage allows monitoring and
managing of all APs and their RF experience from a single point in the network, as well as understanding
how every AP relates to any other AP in the RF Group/Neighborhood. This feature is unique in the
industry because most other implementations run AP to AP at the edge in a distributed fashion with only
configuration elements being managed centrally.
operates in a centralized manner even in large deployments. This advantage allows monitoring and
managing of all APs and their RF experience from a single point in the network, as well as understanding
how every AP relates to any other AP in the RF Group/Neighborhood. This feature is unique in the
industry because most other implementations run AP to AP at the edge in a distributed fashion with only
configuration elements being managed centrally.
NDP is sent from every AP/Radio/Channel every 60 seconds or less. The NDP packet is a special
broadcast message that all APs listen for and it allows us to understand how every radio on every channel
hears every other radio. It also gives the RF group the actual RF path loss between APs.
broadcast message that all APs listen for and it allows us to understand how every radio on every channel
hears every other radio. It also gives the RF group the actual RF path loss between APs.
Neighbor messages are sent to a special Multicast address 01:0B:85:00:00:00, and are done so at:
•
The Highest Power allowed for the Channel/Band.
•
The Lowest data rate supported in the band.
For 802.11b, this means that the message is sent at power level 1 (always the highest power for a
particular radio)@ 1 Mbps, and for 5 GHz radio’s 6 Mbps. This function is hard coded into the radio
firmware and there is no user control. NDP power and modulation are not changed by user configured
data rates or power levels.
particular radio)@ 1 Mbps, and for 5 GHz radio’s 6 Mbps. This function is hard coded into the radio
firmware and there is no user control. NDP power and modulation are not changed by user configured
data rates or power levels.
Source Port
Destination Port
RRM Manger 11b (11a) 12134 (12135)
12124(12125)
RRM Client 11b (11a)
12124 (12125)
12134 (12135)