Essentially there are four egress or TX queues per interface, and in this particular instance the transmit queue 1 is the queue for all other traffic which has not been marked or classified.
Therefore in order to guarantee the minimum bandwidth for tx-queue 3 (33 percent) which is the strict priority queue for RTP, then queues will be serviced accordingly. This means that packets in TX queue 1 will be the first to be dropped as you have seen.
The fact the minimum bandwidth for the tx-queue 3 is 1/3 of the interface would seem some what excessive, thus starving other queues of bandwidth. Similarly the shaping or maximum bandwidth for queue 3 is also set to 1/3 and I would not expect voice traffic to peak 300 mbps on a gigabit interface.
Typically queue 3 is for VoIP and queue 4 is used for signalling,routing, BPDU updates etc, this obviously depends on your dscp mappings.
Depending on your traffic profile, which seems that your traffic typically falls into queue 1, then I would divide the bandwidth accordingly.
I would recommend initially adjusting the tx-queues as follows, and monitor the situation. You can always adjust the minimum and shaped maximum levels if you feel that voice quality is being comprised:-
interface GigabitEthernet6/27
tx-queue 1
bandwidth 500 mbps
tx-queue 2
bandwidth 200 mbps
tx-queue 3
bandwidth 50 mbps
priority high
shape 50 mbps
Regards
Allan.
Please remember to rate posts if you find this information helpful.
