Specifications

General 7
A WLAN network can either operate on the IEEE 802.11 2.4 GHz (b/g) or a 5 GHz (a) band. De-
pending 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 in
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dependent WLANs which 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 management of infrastructure devices that have additional management ports, for example a
WLAN controller. The management network will still be functional if the normal network breaks
down. Physical separation of WiFi 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, 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 uses streaming audio and video applications, like a video conferencing tool, require
not just high bandwidth but they will also require steady regular access to the network. The large
video packets will take up a lot of the bandwidth and thus the available airtime for a voice call will
be less.
Using the IEEE 802.11e standard or WMM will give voice packets, if configured correctly, a higher
probability to use the air than other types of packets. This standard will stop data clients from mo
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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 traffic
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 LANS
(VLANS). This allows the administrator of the network to set up rules in the switches and routers
that treat the traffic types differently depending on the VLAN association of a device. Having de
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vices on separate VLANs (but still on the same physical LAN) will hide the visibility of a device from
any other device that is not on the same VLAN. It will also reduce the impact of broadcasts sent
in the LAN since only devices in the same VLAN will receive broadcasts. The LAN will actually be
divided in smaller broadcast domains, each with its own range of IP-addresses.
Some of the benefits of using VLANs are:
• The possibility to create a separate subnet for management of devices and thus blocking any
normal users from tampering with configuration.
• The separation of guest traffic from corporate data traffic which only give guests access to the
Internet.
• Reducing the broadcast domain.
• Separating traffic types.
• Protecting devices from access by unauthorized personnel.
• Give priority in the network for some kind of traffic.
• Using role-based access rights and access to a VLANs depending on users group membership.
• Create security rules and allow the use of internal firewalls.
It is important to understand that devices on separate VLANs will not be able to talk with each other
if there are no devices in the network that will route the traffic between the virtual networks.