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This section covers controller redundancy design, radio frequency groups, site survey, and wireless LAN design considerations.

Controller Redundancy Design

WLCs can be configured for dynamic or deterministic redundancy. For deterministic redundancy, the access point is configured with a primary, secondary, and tertiary controller. This requires more upfront planning but allows better predictability and faster failover times. Deterministic redundancy is the recommended best practice. N+1, N+N, and N+N+1 are examples of deterministic redundancy.

Dynamic controller redundancy uses LWAPP to load-balance APs across WLCs. LWAPP populates APs with a backup WLC. This solution works better when WLCs are in a centralized cluster. This solution is easier to deploy than the deterministic solution and allows APs to load-balance. The disadvantages are longer failover times and unpredictable operation. An example is adjacent APs registering with differing WLCs.

N+1 WLC Redundancy

With N+1 redundancy, shown in Figure 4-9, a single WLC acts as the backup of multiple WLCs. The backup WLC is configured as the secondary WLC on each AP. One design constraint is that the backup WLC may become oversubscribed if there are too many failures of the primary controllers. The secondary WLC is the backup controller for all APs.

Figure 4-9. N+1 Controller Redundancy

N+N WLC Redundancy

With N+N redundancy, shown in Figure 4-10, an equal number of controllers back up each other. For example, a pair of WLCs on one floor serves as a backup to a second pair on another floor. The top WLC is primary for AP1 and AP2 and secondary for AP3 and AP4. The bottom WLC is primary for AP3 and AP4 and secondary for AP1 and AP2.

Figure 4-10. N+N Controller Redundancy

N+N+1 WLC Redundancy

With N+N+1 redundancy, shown in Figure 4-11, an equal number of controllers back up each other (as with N+N), plus a backup WLC is configured as the tertiary WLC for the access points. N+N+1 redundancy functions the same as N+N redundancy plus a tertiary controller that backs up the secondary controllers.

Figure 4-11. N+N+1 Controller Redundancy

Radio Management and Radio Groups

The limit of available channels in the ISM frequencies used by the IEEE 802.11b/g standard presents challenges to the network designer. There are three nonoverlapping channels (channels 1, 6, and 11). The recommended best practice per AP is up to 20 data devices, or no more than seven concurrent voice over WLAN (VoWLAN) calls using g.711 or eight concurrent VoWLAN calls using g.729. Additional APs should be added as user population grows to maintain this ratio of data and voice per AP.

Cisco Radio Resource Management (RRM) is a method to manage AP radio frequency channel and power configuration. Cisco WLCs use the RRM algorithm to automatically configure, optimize, and self-heal. Cisco RRM functions are as follows:

• Radio resource monitoring— Cisco LWAPs monitor all channels. Collected packets are sent to the WLC, which can detect rouge APs, clients, and interfering APs.
• Dynamic channel assignment— WLCs automatically assign channels to avoid interference.
• Interference detection and avoidance— As Cisco LWAPs monitor all channels, interference is detected by a predefined threshold (10 percent by default). Interference can be generated by rouge APs, Bluetooth devices, or neighboring WLANs.
• Dynamic transmit power control— The WLCs automatically adjust power levels.
• Coverage hole detection and correction— WLCs may adjust the power output of APs if clients report that a low Received Signal Strength Indication (RSSI) level is detected.
• Client and network load balancing— Clients can be influenced to associate with certain APs to maintain network balance.

Radio Frequency (RF) Groups

An RF group is a cluster of WLC devices that coordinate their RRM calculations. When the WLCs are placed in an RF group, the RRM calculation can scale from a single WLC to multiple floors, buildings, or even the campus. With an RF group, APs send neighbor messages to other APs. If the neighbor message is above –80 dBm, the controllers form an RF group. The WLCs elect an RF group leader to analyze the RF data. The RF group leader exchanges messages with the RF group members using UDP port 12114 for 802.11b/g and UDP port 12115 for 802.11a.

RF Site Survey

Similar to performing an assessment for a wired network design, RF site surveys are done to determine design parameters for wireless LANs and customer requirements. RF site surveys help determine the coverage areas and check for RF interference. This helps determine the appropriate placement of wireless APs.

The RF site survey has the following steps:

Step 1.	Define customer requirements, such as service levels and support for VoIP.
Step 2.	Identify coverage areas and user density, including peak use times and conference room locations.
Step 3.	Determine preliminary AP locations, which need power, wired network access, mounting locations, and antennas.
Step 4.	Perform the actual survey by using an AP to survey the location and received RF strength based on the targeted AP placement. Consider the effects of electrical machinery. Microwave ovens and elevators may distort the ration signal from the APs.
Step 5.	Document the findings by recording the target AP locations, data rates, and signal readings.

Using EoIP Tunnels for Guest Services

Basic solutions use separate VLANs for guest and corporate users to segregate guest traffic from corporate traffic. The guest SSID is broadcast, but the corporate SSID is not. All other security parameters are configured. Another solution is to use Ethernet over IP (EoIP) to tunnel the guest traffic from the LWAPP to an anchor WLC.

As shown in Figure 4-12, EoIP is used to logically segment and transport guest traffic from the edge AP to the anchor WLC. There is no need to define guest VLANs in the internal network, and corporate traffic is still locally bridged. The Ethernet frames from the guest clients are maintained across the LWAPP and EoIP tunnels.

Figure 4-12. EoIP Tunnels

Wireless Mesh for Outdoor Wireless

Traditionally, outdoor wireless solutions have been limited to point-to-point and point-to-multipoint bridging between buildings. With these solutions, each AP is wired to the network. The Cisco Wireless Mesh networking solution, shown in Figure 4-13, eliminates the need to wire each AP and allows users to roam from one area to another without having to reconnect.

Figure 4-13. Wireless Mesh Components

The wireless mesh components are as follows:

• Wireless Control System (WCS) is the wireless mesh SNMP management system that allows network-wide configuration and management.
• Wireless LAN Controller (WLC) links the mesh APs to the wired network and performs all the tasks previously described for a WLC.
• Rooftop AP (RAP) connects the mesh to the wired network and serves as the root (or gateway). It also communicates with the MAPs.
• Mesh Access Points (MAP) are remote APs. They communicate with the RAP to connect to the wired network.

Mesh Design Recommendations

The following are Cisco recommendations (and considerations) for mesh design:

• There is a 2- to 3-ms typical latency per hop.
• For outdoor deployment, four or fewer hops are recommended for best performance. A maximum of eight hops is supported.
• For indoor deployment, one hop is supported.
• 20 MAP nodes per RAP are recommended for best performance. Up to 32 MAPs are supported.

Campus Design Considerations

When designing for the Cisco Unified Wireless Network, you need to be able to determine how many LWAPs to place and how they will be managed with the WLCs. Table 4-4 summarizes campus design considerations.

Table 4-4. WLAN Design Considerations

Design Item	Description
Number of APs	The design should have enough APs to provide full RF coverage for wireless clients for all the expected locations in the enterprise. Cisco recommends 20 data devices per AP and 7 g.711 concurrent or 8 g.729 concurrent VoWLAN calls.
Placement of APs	APs are placed in a centralized location of the expected area for which they are to provide access. APs are placed in conference rooms to accommodate peak requirements.
Power for APs	Traditional wall power can be used, but the preferred solution is to use power over Ethernet (PoE) to power APs and provide wired access.
Number of WLCs	The number of WLCs depends on the selected redundancy model based on the client's requirements. The number of controllers is also dependent on the number of required APs and the number of APs supported by the differing WLC models.
Placement of WLCs	WLCs are placed on secured wiring closets or in the data center. Deterministic redundancy is recommended, and intercontroller roaming should be minimized. WLCs can be placed in a central location or distributed in the campus distribution layer.

Table 4-5 summarizes AP features for Cisco APs.

Table 4-5. Supported Features and Specifications for Cisco APs

Feature	10x0 Series	1121 Series	1130 Series	1230 Series	1240 Series	1300 Series	1500 Series
Autonomous/LWAPP	LWAPP	Both	Both	Both	Both	Both	LWAPP
External antenna	Yes	No	No	Yes	Yes	Yes	Yes
Outdoor install	No	No	No	No	No	Yes	Yes
REAP/Hybrid REAP (H-REAP)	REAP	No	H-REAP	No	H-REAP	No	Yes
Dual radio	Yes	No (only 11b/g)	Yes	Yes	Yes	No (only 11b/g)	Yes
Power (watts)	13	6	15	14	15	—	—
Memory (Mb)	16	16	32	16	32	16	16
WLANs supported	16	8	8	8	8	8	16

Branch Design Considerations

For branch networks you need to consider the number and placement of APs, which depends on the location and expected number of wireless clients at the branch office. It may not be costjustifiable to place a WLC at each branch office of an enterprise. One requirement is that the round-trip time (RTT) between the AP and the WLC should not exceed 100 ms. For centralized controllers, it is recommended that you use REAP or Hybrid REAP (H-REAP).

Local MAC

LWAPP supports local media access control (local MAC), which can be used in branch deployments. Unlike with split-MAC, the AP provides MAC management support for association requests and actions. Local MAC terminates client traffic at the wired port of the access point versus at the WLC. This allows direct local access to branch resources without requiring the data to travel to the WLC at the main office. Local MAC also allows the wireless client to function even if a WAN link failure occurs.

REAP

REAP is designed to support remote offices by extending LWAPP control timers. It is the preferred solution for LWAPs to connect to the WLC over the WAN. With REAP control, traffic is still encapsulated over a LWAPP tunnel and is sent to the WLC. Management control and RF management are done over the WAN. Client data is locally bridged. With REAP, local clients still have local connectivity if the WAN fails.

WLCs support the same number of REAP devices as APs. REAP devices support only Layer 2 security policies, do not support NAT, and require a routable IP address.

Hybrid REAP

H-REAP is an enhancement to REAP that provides additional capabilities such as NAT, more security options, and the ability to control up to three APs remotely.

H-REAP operates in two security modes:

• Standalone mode— H-REAP does the client authentication itself when the WLC cannot be reached.
• Connected mode— The device uses the WLC for client authentication.

H-REAP is more delay-sensitive than REAP. The RTT must not exceed 100 ms between the AP and the WLC.

Branch Office Controller Options

For branch offices, Cisco recommends one of four options:

• Cisco 2006— Supports six APs.
• Cisco 4402-12 and 4402-25— These devices support 12 and 25 APs, respectively.
• WLC Module in Integrated Services Router (ISR)— Supports six APs.
• 3750 with WLAN controller— Depending on the model, this can support 25 or 50 APs.