Layer 2 QoS Congestion management - Help

Answered Question
Oct 31st, 2011

Hello everyone.

I´ve an escenario with some cisco access switches and cisco router that support connectivity for IP telephony. But the PBX is Nortel. Suppose i am trying to manage voice and signaling traffic with the recommended values (CoS5 and CoS3), and that i´m changing DSCP values on access port so i can use DSCP 24 for signaling and DSCP 46 for voice (not trusting DSCP but remarking with a policy MAP). Then on switches i´ve the following congestion managemente config:

mls qos srr-queue output cos-map queue 1 threshold 3 5

mls qos srr-queue output cos-map queue 2 threshold 1 2 4

mls qos srr-queue output cos-map queue 2 threshold 2 3

mls qos srr-queue output cos-map queue 2 threshold 3 6 7

mls qos srr-queue output cos-map queue 3 threshold 3 0

mls qos srr-queue output cos-map queue 4 threshold 3 1

mls qos srr-queue output dscp-map queue 1 threshold 3 46

mls qos srr-queue output dscp-map queue 2 threshold 1 16

mls qos srr-queue output dscp-map queue 2 threshold 1 18 20 22

mls qos srr-queue output dscp-map queue 2 threshold 1 25

mls qos srr-queue output dscp-map queue 2 threshold 1 32

mls qos srr-queue output dscp-map queue 2 threshold 1 34 36 38

mls qos srr-queue output dscp-map queue 2 threshold 2 24

mls qos srr-queue output dscp-map queue 2 threshold 3 48 56

mls qos srr-queue output dscp-map queue 3 threshold 3 0

mls qos srr-queue output dscp-map queue 4 threshold 1 8

mls qos srr-queue output dscp-map queue 4 threshold 3 10 12 14

mls qos queue-set output 1 threshold 2 70 80 100 100

mls qos queue-set output 1 threshold 4 40 100 100 100

But with this config, the PBX is generating a lot of QoS error logs related to delay and jitter. Because of this i want to change how Signaling (DSCP 24 - CoS 3) will be managed by switches. Could i use this config instead?

mls qos map cos-dscp 0 8 16 24 34 46 48 56

mls qos srr-queue output cos-map queue 1 threshold 3 3 5

mls qos srr-queue output cos-map queue 2 threshold 1 2 4

mls qos srr-queue output cos-map queue 2 threshold 3 6 7

mls qos srr-queue output cos-map queue 3 threshold 3 0

mls qos srr-queue output cos-map queue 4 threshold 3 1

mls qos srr-queue output dscp-map queue 1 threshold 3 24 41 42 43 44 45 46 47

mls qos srr-queue output dscp-map queue 2 threshold 1 16 18 20 22 25 32 34 36

mls qos srr-queue output dscp-map queue 2 threshold 1 38

mls qos srr-queue output dscp-map queue 2 threshold 2 40

mls qos srr-queue output dscp-map queue 2 threshold 3 26 27 28 29 30 31 48 49

mls qos srr-queue output dscp-map queue 2 threshold 3 50 51 52 53 54 55 56 57

mls qos srr-queue output dscp-map queue 2 threshold 3 58 59 60 61 62 63

mls qos srr-queue output dscp-map queue 3 threshold 3 0 17 19 21 23 33 35 37

mls qos srr-queue output dscp-map queue 3 threshold 3 39

mls qos srr-queue output dscp-map queue 4 threshold 1 8

mls qos srr-queue output dscp-map queue 4 threshold 2 9 11 13 15

mls qos srr-queue output dscp-map queue 4 threshold 3 1 2 3 4 5 6 7 10

mls qos srr-queue output dscp-map queue 4 threshold 3 12 14

mls qos queue-set output 1 threshold 1 138 138 92 138

mls qos queue-set output 1 threshold 2 70 80 100 100

mls qos queue-set output 1 threshold 4 40 100 100 100

mls qos

What i´m trying to do here is to locate signaling traffic on output priority queue (1). What about the queue-set output, will that work?. Thanks.

I have this problem too.
0 votes
Correct Answer by Marwan ALshawi about 2 years 5 months ago

well signalling is ok to be placed in diffrent queue other than the PQ

just make sure the VOIP RTP marked with cos5/dscp 46 is placed in the PQ and make sure that you have the right cos-to-dscp maping from cos 5 to dscp 46

hope this help

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Average Rating: 5 (1 ratings)
Marwan ALshawi Mon, 10/31/2011 - 19:47

mls qos srr-queue input cos-map queue 2 threshold 3 3 5
mls qos srr-queue output cos-map queue 1 threshold 3 5

mls qos srr-queue output dscp-map queue 1 threshold 3 40 41 42 43 44 45 46 47

and on the interface level you the enable PRQ

priority-queue out

i am assuming you are using 3560 switch

HTH

andres@franco Mon, 10/31/2011 - 20:48

Ok. Let me proccess  this to see if I understand it!

You´re telling me to manage priority for signaling only in the input priority queue (2) (does it matter if i put cos 3 in queue 2 for output?) while voice will be manage here an also y in the ouput priority queue (1)???? So  the hole thing could look like this?

mls qos map cos-dscp 0 8 16 24 34 46 48 56

mls qos srr-queue input cos-map queue 2 threshold 3 3 5 

mls qos srr-queue output cos-map queue 1 threshold 3 5

mls qos srr-queue output cos-map queue 2 threshold 1 2 4

mls qos srr-queue output cos-map queue 2 threshold 2 3

mls qos srr-queue output cos-map queue 2 threshold 3 6 7

mls qos srr-queue output cos-map queue 3 threshold 3 0

mls qos srr-queue output cos-map queue 4 threshold 3 1

mls qos srr-queue output dscp-map queue 1 threshold 3 40 41 42 43 44 45 46 47

mls qos srr-queue output dscp-map queue 2 threshold 1 16 18 20 22 25 32 34 36

mls qos srr-queue output dscp-map queue 2 threshold 1 38

mls qos srr-queue output dscp-map queue 2 threshold 2 24

mls qos srr-queue output dscp-map queue 2 threshold 3 26 27 28 29 30 31 48 49

mls qos srr-queue output dscp-map queue 2 threshold 3 50 51 52 53 54 55 56 57

mls qos srr-queue output dscp-map queue 2 threshold 3 58 59 60 61 62 63

mls qos srr-queue output dscp-map queue 3 threshold 3 0 17 19 21 23 33 35 37

mls qos srr-queue output dscp-map queue 3 threshold 3 39

mls qos srr-queue output dscp-map queue 4 threshold 1 8

mls qos srr-queue output dscp-map queue 4 threshold 2 9 11 13 15

mls qos srr-queue output dscp-map queue 4 threshold 3 1 2 3 4 5 6 7 10

mls qos srr-queue output dscp-map queue 4 threshold 3 12 14

mls qos queue-set output 1 threshold 1 138 138 92 138

mls qos queue-set output 1 threshold 2 70 80 100 100

mls qos queue-set output 1 threshold 4 40 100 100 100

mls qos

I´ve priority-queue out and queue-set 1 applied to all interfaces (including trunks) and yes, i´m usign 3560 switches. Will this be your recommended setting to prioritize signaling?

Correct Answer
Marwan ALshawi Mon, 10/31/2011 - 22:07

well signalling is ok to be placed in diffrent queue other than the PQ

just make sure the VOIP RTP marked with cos5/dscp 46 is placed in the PQ and make sure that you have the right cos-to-dscp maping from cos 5 to dscp 46

hope this help

andres@franco Tue, 11/01/2011 - 06:37

Thanks again dude, thanks for your patience.

This will be my complete config taking in account your suggestions!

mls qos

class-map match-all VoIP
match ip dscp ef
class-map match-all VoIP-SIGNALING
match ip dscp cs5

policy-map QoS-SW3560
class VoIP
set dscp ef
class VoIP-SIGNALING
set dscp cs3

mls qos map cos-dscp 0 8 16 24 34 46 48 56

mls qos srr-queue input cos-map queue 2 threshold 3 3 5

mls qos srr-queue output cos-map queue 1 threshold 3 5
mls qos srr-queue output cos-map queue 2 threshold 1 2 4
mls qos srr-queue output cos-map queue 2 threshold 2 3
mls qos srr-queue output cos-map queue 2 threshold 3 6 7
mls qos srr-queue output cos-map queue 3 threshold 3 0
mls qos srr-queue output cos-map queue 4 threshold 3 1
mls qos srr-queue output dscp-map queue 1 threshold 3 40 41 42 43 44 45 46 47
mls qos srr-queue output dscp-map queue 2 threshold 1 16
mls qos srr-queue output dscp-map queue 2 threshold 1 18 20 22
mls qos srr-queue output dscp-map queue 2 threshold 1 25
mls qos srr-queue output dscp-map queue 2 threshold 1 32
mls qos srr-queue output dscp-map queue 2 threshold 1 34 36 38
mls qos srr-queue output dscp-map queue 2 threshold 2 24
mls qos srr-queue output dscp-map queue 2 threshold 3 48 56
mls qos srr-queue output dscp-map queue 3 threshold 3 0
mls qos srr-queue output dscp-map queue 4 threshold 1 8
mls qos srr-queue output dscp-map queue 4 threshold 3 10 12 14

mls qos queue-set output 1 threshold 1 138 138 92 138
mls qos queue-set output 1 threshold 2 70 80 100 100
mls qos queue-set output 1 threshold 4 40 100 100 100

interface range GigabitEthernet0/X

no mls qos trust dscp

no auto qos voip trust
queue-set 1
srr-queue bandwidth share 1 70 25 5
srr-queue bandwidth shape 3 0 0 0
service-policy input QoS-SW3560
priority-queue out

Now, taking into consideration other comments you have done, what will take precedence for this interface configuration? the queue-set 1 or the priority queue out? should i remove one? and, This whole config looks ok to you?

Thanks again.

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Posted October 31, 2011 at 6:46 PM
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