Overview
Furthermore, the design problems get even more complex if Wi-Fi RFID tagging and location
traffic are also using the WLAN, because they require a completely different design.
The best solution to avoid these design problems is to separate traffic types, either physically
( see
on page 6) or logically (see
on page 6), so
they do not interfere with each other.
Physical Separation
A WLAN network can either operate on the IEEE 802.11 2.4 GHz or a 5 GHz band. Depending
on the WLAN APs used, a network may support either one of those bands or both if the AP is
equipped with dual radios. In such a case, the WLAN network can be thought of as two indepen-
dent WLANs that are physically separated by the usage of different frequencies.
An AP that has only one radio must be using protocol features that mitigate the effects of having
different traffic types and patterns in the WLAN.
Physical separation of traffic types in a wire line network is achieved by pulling two cables side
by side. It is quite common that IT departments build a second totally independent network used
only for the management of infrastructure devices that have additional management ports, for
example a WLAN controller. The management network will still be functional if the normal net-
work breaks down. Physical separation of Wi-Fi traffic is, however, not possible in any another
way than using different radio channels for different traffic types.
If voice has to share the channels with any other type of data, Wi-Fi Multimedia (WMM) priority
protocol must be used.
Logical Separation
All clients in a wireless cell have equal access rights to the air if priority schemes are not used.
Laptops that use streaming audio and video applications, like a video conferencing tool, require
not only high bandwidth but also steady regular access to the network. The large video packets
take up a lot of the bandwidth and thus the available airtime for a voice call is less.
Using the IEEE 802.11e standard or WMM gives voice packets, if configured correctly, a higher
probability to use the air than other types of packets. This standard stops data clients from mo-
nopolizing the WLAN.
In a network it is possible to use information found in the headers of the packets to identify traffic
types and to treat the traffic differently on its route to the destination based on that information.
The information that is written to or read from the headers can be used to prioritize a certain traf-
fic type above another type.
Logical Separation of Voice and Data Traffic on the Same
Channel
In a wired converged data network, traffic types are often logically separated using Virtual Local
Area Network (VLANS). This allows the administrator of the network to set up rules in the switch-
es and routers that treat the traffic types differently depending on the VLAN association of a de-
vice. Having devices on separate VLANs (but still on the same physical LAN) hides the visibili-
ty of a device from any other device that is not on the same VLAN. It also reduces the impact of
broadcasts sent in the LAN since only devices in the same VLAN receive broadcasts. The LAN
is actually divided into smaller broadcast domains, each with its own range of IP-addresses.
Some of the benefits of using VLANs are:
• Creating a separate subnet for managing devices and thus blocking any normal user from
tampering with configuration.
• Separating guest traffic from corporate data traffic, which only gives guests access to the In-
ternet.
A31003-M2000-P103-01-76A9, 29/04/2020
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System Planning, Planning Guide
