Re: QoS VOIP on catalyst 4500

eringaard · ‎10-09-2005

We have the following QoS config on a 4500 running IOS.

We have Siemens IP phones connected which sent out COS 3 & 5 and DSCP 46 & 26 values for voice and signalling.

To configure the LAN end to end I have enabled the following COS config on the 4500.

Since we don't have any other QoS practises in our network, I don't want to configure bandwith, buffer overflow etc, or do anything with marking or changing values.

2 questions are below this config:

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switch4500#sh qos interface fa2/2

QoS is enabled globally

Port QoS is enabled

Administrative Port Trust State: 'dscp'

Operational Port Trust State: 'dscp'

Trust device: none

Default DSCP: 0 Default CoS: 0

Appliance trust: none

Tx-Queue Bandwidth ShapeRate Priority QueueSize

(bps) (bps) (packets)

1 N/A disabled N/A 240

2 N/A disabled N/A 240

3 N/A disabled high 240

4 N/A disabled N/A 240

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switch4500#sh qos maps cos dscp

CoS-DSCP Mapping Table

CoS: 0 1 2 3 4 5 6 7

--------------------------------

DSCP: 0 8 16 26 32 46 48 56

switch4500#sh qos maps dscp tx

DSCP-TxQueue Mapping Table (dscp = d1d2)

d1 : d2 0 1 2 3 4 5 6 7 8 9

-------------------------------------

0 : 01 01 01 01 01 01 01 01 01 01

1 : 01 01 01 01 01 01 02 02 02 02

2 : 02 02 02 02 02 02 03 02 02 02

3 : 02 02 03 03 03 03 03 03 03 03

4 : 03 03 03 03 03 03 03 03 04 04

5 : 04 04 04 04 04 04 04 04 04 04

6 : 04 04 04 04

----------------------------------------------------------------------------------------

Above qos map is fairly default except from the maps I created to put voice traffic in prio queue 3. for now this is all I want to confure.

Question 1: By looking at the map it seems values 0-15, 16-31, 26 32-47 and 58 - 63 are distributed over the different queues. Since we have no other qos traffic then dscp

46 and 26 I assume all other traffic is default 0. So where does this traffic go? - only to queue 1? Or is is distributed still? - Do I have to set all other queues to dscp 0?

Question 2: This would be fairly easy to check if there is a command which would show you the different queues and stats of packets going through, however I have not found such a command. Is there a way to monitor this process at all?

Chris Deren · ‎10-09-2005

First of all by classifing COS you do not really accomplish any QoS. It's only the first step. For LAN QoS you want to create expedite queue, for voice on 4500 switch you need to do it by appliying "tx-queue 3" and "priority high" commands to the interfaces. This way all of you DSCP 32-47 (COS 3 - default for RTP stream).

Refer to this doc:

http://www.cisco.com/en/US/products/hw/switches/ps4324/products_configuration_guide_chapter09186a00803671bd.html

Chris

eringaard · ‎10-10-2005

If you read my post you can see I already configured this. But that's not my question. There are 4 queues, one the expidite which I am sending Cos 3 (dscp 32 - 47) traffic. But the other queues all seem to have different ranged attached to them does this mean there is no traffic at all going to queues 2 and 4 (I dont have any cos or dscp traffic in that range) Anyway, it's all in my original post.