10-28-2007 10:30 AM - edited 03-13-2019 04:35 PM
Hello
I'm new ro QOS, and is implementing a IP telephony solution for a customer. We have got a Catalyst 4510, where the phones are connected, and then the PC's are connected to the phones.
I have configured the "auto qos voip ciscophone" on the interfaces connected to the Cisco phones (7941's). However, we are experiencing a big performance descrease on the PC's (about 1/2 or 1/3 the performance or so), when the "auto qos voip ciscophone" is configured on the interfaces. When I remove the auto qos from the interfaces, everything works at normal speed.
Is it a bad idea to configure the "auto qos voip ciscophone" on the interfaces, when the PC's are connected to the phones?
10-28-2007 11:10 PM
post the config on one of the interfaces
I believe duplex becomes hardcoded and if so you can auto qos on one of the interfaces and set the duplex back to auto.
hth
10-28-2007 11:17 PM
interface GigabitEthernet6/27
switchport mode access
switchport voice vlan 10
qos trust cos
qos trust device cisco-phone
auto qos voip cisco-phone
tx-queue 3
bandwidth percent 33
priority high
shape percent 33
spanning-tree portfast
service-policy output autoqos-voip-policy
10-29-2007 10:27 AM
On a "sh interface counters detail module" are you dropping frames on one of the qos queues?
10-29-2007 11:30 AM
When I do a "sh interface counters detail", I have a lot of tx drops in the "Tx-Drops-Queue-1".
10-29-2007 03:03 PM
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.
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10-29-2007 09:25 PM
You can try upgrading the 7941 firmware to rule out any bugs
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