Aruba Networks Version 3.3 AP Power and Connectivity, AP Location and Density Considerations

VLAN at the Local Controller where a VLAN trunk already exists. This also allows for mobile IP functionality without client software as the intervening VLAN between the AP and the controller is never seen by the client.

AP Power and Connectivity

The AP can use DHCP for IP addressing and can automatically discover the Mobility Controller through a number of methods making it easily added to any existing employee port and VLAN.

If the Access Point and Mobility Controller share the same Layer 2 VLAN, then nothing else needs to be done as the AP will automatically discover the controller via the Aruba Discovery Protocol (ADP). If the AP and controller are separated by a Layer 3 network then two other methods are available for controller discovery. An entry can be entered into the organization’s DNS for ‘aruba-master’ with the AP address of the Mobility Controller, or a DHCP option 43 value may be configured with the address of the Mobility Controller.

Power should be supplied either using 802.3af Power-over-Ethernet (PoE) or using a power adapter for the access point. PoE is the simplest method if it is already in place because the AP will be able to use a single cable for both power and data.

AP Location and Density Considerations

Determining the correct number of APs to deploy for a given area requires careful planning. RF designers generally use a metric called ‘AP density’ which refers to the number of square feet that each AP is expected to serve.

AP Density is affected by:

zWhat applications are running on the network

zWhich frequency bands are in use

zThe degree of overlap in the cells for self-healing

zAntenna choice

It is possible for AP density to vary within a campus or even within a building. Aruba recommends working with a professional WLAN engineering organization to select the proper AP density for all coverage areas.

In addition to AP density, the RF engineer must also select a Placement Methodology. This refers to whether the APs are spaced uniformly or not, and whether they are located along the perimeter of an area or spread throughout the interior. The methodology has important consequences for customers that plan to use location services. With the AP Density and Placement Methodology known, the RF engineer can use the Aruba RF Plan tool to create a design for each floor or area to be covered. This is explained in more detail in a later chapter.

Office Deployment

It used to be common practice to deploy APs in the plenum space above the ceiling grid. As the cost of APs came down, and with the advent of the thin AP with attractive industrial design, it is now common to deploy the AP directly in the user space. Access Points such as the Aruba AP65 have an integral T-bar clip to attach directly to standard drop ceilings common in carpeted office areas, as well as supporting many other mounting methods. A best practice is to clearly label the AP during installation using letters large enough to be seen from the ground to facilitate moves, adds and changes.

Performance is best when a clear line-of-sight (LOS) exists between the AP and its clients. Aruba does not recommend placing the AP on desktops, or placing an AP on the top of a set of cubicles. LOS is easily obstructed in these cases, resulting in performance that may not meet the standards of the design.

Campus Wireless Networks Validated Reference Design Version 3.3 Design Guide Mobility Controller and Access Point Deployment 35