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Campus Wireless Networks Validated Reference Design Version 3.3 | Design Guide Mobility Controller and Access Point Deployment | 35
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:
z What applications are running on the network
z Which frequency bands are in use
z The degree of overlap in the cells for self-healing
z Antenna 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.