Understanding Load Balancing for Wireless Radios

Load balancing distributes a workload across multiple
entities, in this case wireless radios, to achieve optimal utilization,
maximize throughput, minimize response time, and avoid overload.

RF load-balancing for access points has the ability to reduce
network congestion over an area by distributing client sessions across
access point radios with overlapping coverage. With load-balancing,
you can ensure that all access points on the network handle a proportionate
share of wireless traffic, and that no single access point gets overloaded.
Load balancing of access points is enabled by default in WLAN Service
profiles—that means that all access points using a WLAN Service
profile are load-balanced.

This topic describes:

Why Would I Need Load Balancing?

As new clients arrive, load-balancing distributes the clients
among access points such that the access points share the client load.
The wireless operating system, MSS, encourages clients to associate
with the least loaded (by client count) access point, so that clients
are well distributed across access points. This way, no one access
point is more overloaded and there is less interruption of wireless
services on the network. For example, in an auditorium or lecture
hall, there might be a large number of clients in a relatively small
amount of space. While a single access point might be sufficient for
providing an RF signal to the entire area, more access points might
be required to deliver enough aggregate bandwidth for all of the clients.
When additional access points are installed in the room, RF load-balancing
spreads clients evenly across the access points, increasing the available
aggregate bandwidth by increasing the number of access points. Without
load-balancing, you could have multiple access points in a classroom
with all clients associated to just one of the access points.

When Would I Avoid Load Balancing?

We do not recommend load-balancing for low-latency applications
such as voice or live-streaming (unbuffered) video. Load balancing
is not advisable for voice transmission because load-balancing can
impact roam times, which can impact voice quality for roaming clients.
Load balancing can also make streaming video jittery with dropped
frames.

How Load Balancing Works

The wireless operating system, MSS, balances the client load
by adjusting how access points are perceived by clients advertising
the same SSID. The capacity of an access point handling new clients
is compared to other access points in the SSID. As new clients arrive,
MSS encourages them to associate with the least loaded (by client
count) access points, such that clients are well distributed across
access points. By default, MSS only encourages clients to associate
with an access point if there are access points available with capacity
to accept more clients. Clients are never prevented from associating
with an access point if it is the only one available.

Can I Group Access Points for Load Balancing?

You can optionally place access point radios into load-balancing
groups. When two or more access point radios are placed in the same
load-balancing group, MSS assumes that they have exactly the same
coverage area, and attempts to distribute the client load across them
equally. The AP radios do not have to be on the same controller. A
balanced set of AP radios can span multiple controllers in a mobility
domain. When you have grouped APs for load-balancing, you can also
indicate how strictly the balancing is enforced, low, medium, high,
and maximum enforcement.

Where Do I Configure Load Balancing in Network Director?

Load balancing is enabled and configured in multiple places
for several kinds of load-balancing. The load-balancing option discussed
here applies to wireless access points and radios.

Note

Load balancing configured in Access profiles applies to the
RADIUS servers configured within that profile. For directions, see Creating and Managing Access Profiles.

RF load-balancing for access points is enabled by default in
Juniper Networks WLAN mobility domains, affecting all radios within
that domain. You can, however, disable load-balancing in a WLAN Service
profile. If you want a WLAN’s SSID on access points to be exempt
from load-balancing, you can indicate that a WLAN Service profile
is Load Balancing Exempt—see the directions
for Network Director Creating and Managing a WLAN Service Profile.

You can assign a single access point to a specific load-balance
group when you add that access point to a controller—see Adding and Managing an Individual Access Point. You can also configure load-balancing on a controller—see Configuring a Controller .