Curious to know if others are using "qos basic" or "qos advanced" to support voip (Deskphones using voice vlan).
I'm trying to see if I can get by with just "qos basic" and "priority-queue out num-of-queues 3" so as to not overly complicate things in this smaller environment (CBS220/250/350). But I'm also not sure if just turning those two knobs on is sufficient for the switch to provide preferred / expedited treatment to cos 5 / dscp 46 voice frames.
basically doing this on CBS220 (v2.0.2.14) to start with (yealink phones can use lldp med to get vlan/cos/dscp values):
vlan 1
name "default"
vlan 100
name "Data"
vlan 200
name "Voice"
qos basic
qos trust cos-dscp
priority-queue out num-of-queues 3
voice vlan state disabled
lldp med network-policy 1 app voice vlan 200 vlan-type tag priority 5 dscp 46
! switchport with voip phone and desktop
interface gi1
switchport mode trunk
switchport trunk native vlan 100
switchport trunk allowed vlan remove 1-199,201-4094
spanning-tree portfast
lldp med network-policy add 1
loopback-detection enable
the "priority queue out" statement in global config mode is what was elusive to me. I got this explanation from TAC below, confirming that I should set to "3" so as to make sure to include cos 5 (queue 6..also includes queues 7 and 8 as priority queues). It was just interesting to me that the defaults of the switch without that "priority-queue out" command is that "all queues are expedite queues" (per the CLI guide). It would seem like logic would state that we want to "set apart" the voice traffic and one may think that just turning on "qos basic" would do the trick. But I think that "priority-queue out" is also key.
---TAC---
Queue 6 is the default queue where DSCP 46 and CoS 5 are mapped. This is a strict priority queue, which is a good practice for voice traffic to ensure low latency and jitter.
For the remaining queues (1-5), using Weighted Round Robin (WRR) helps ensure that while voice traffic gets the highest priority, other traffic types also get their fair share of bandwidth. This setup prevents lower-priority traffic from being starved and ensures balanced traffic handling.
Typically, queues 6 and 7 are reserved for high-priority traffic such as voice and video. Queue 8 is often reserved for control traffic or can be used as an additional high-priority queue. Configuring queues 1-5 with WRR ensures balanced traffic handling and prevents lower-priority traffic from being starved.
To summarize:
Queue 6: Strict Priority Queue for voice traffic (DSCP 46, CoS 5).
Queues 1-5: WRR for other types of traffic to ensure fair bandwidth distribution.
Queue 7: Can be used for other high-priority traffic such as video.
Queue 8: Often reserved for control traffic or additional high-priority needs.
