QOS (Quality of Service) is a hack or work around if you do not have enough bandwidth to deploy delay sensitive applications such as voice. QOS can buy you sometime whilst you sought out your bandwidth problems.
QOS has to be configured and deployed through the whole network for it to work ( Handsets, switches, routers etc).
To configure a IPBrick to tag packets with the recommended layer 2 and Layer 3 markers, Edit the following file
;Main file for manual changes to ; /home1/_AsteriskConfs/sip_main.conf tos_sip=cs3 tos_audio=ef tos_video=af41 tos_text=af41 cos_sip=3 cos_text=3 cos_video=4 cos_audio=5
Note: This will only affect asterisk, You may still see SIP signalling tagged as COS 4. This will be the kamaillo proxy. I’m not sure where to find the setting to match to cs3 instead. You could do cos mapping on your switch instead.