Hi Antonis,
Have a look at these docs. Hopefully they will help get you started;
Cisco Aironet 1300 Series Outdoor Access Point/Bridge Software Configuration Guide, 12.3(4) JA
Chapter 14 - Configuring QoS
This chapter describes how to configure quality of service (QoS) on your access point/bridge. With this feature, you can provide preferential treatment to certain traffic at the expense of others. Without QoS, the access point/bridge offers best-effort service to each packet, regardless of the packet contents or size. It sends the packets without any assurance of reliability, delay bounds, or throughput.
From this doc;
http://www.cisco.com/en/US/products/ps5861/products_configuration_guide_chapter09186a00804158a6.html
Giving Priority to Voice Traffic
This section demonstrates how you can apply a QoS policy to your wireless network's voice VLAN to give priority to wireless phone traffic.
In this example, the network administrator creates a policy named voice_policy that applies voice class of service to traffic from Spectralink phones (protocol 119 packets). The user applies the voice_policy to the incoming and outgoing radio ports and to the outgoing Ethernet port for VLAN 77.
Use the Apply Policies to Interface/VLANs drop-down menus to apply policies to the access point Ethernet and radio ports. If VLANs are configured on the access point, drop-down menus for each VLANs' virtual ports appear in this section. If VLANs are not configured on the access point, drop-down menus for each interface appear.
From this doc;
http://www.cisco.com/en/US/products/ps5861/products_configuration_guide_chapter09186a00804158a6.html#wp1047736
Hope this helps!
Rob
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