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What is the default QoS behaviour of the 6608 PRI and 6624 FXS Catalyst 6000 cards?

Core Issue

The 6608 and 6624 cards are not configurable for Quality of Service (QoS). Therefore, you need to understand the default tagging behaviour of these cards and, if necessary, take action on the Catalyst switch to conform to the QoS policy being implemented network wide.

Resolution

The 6608 and 6624 internal port is treated as trust-cos to the Catalyst 6000. So the default COS-to-DSCP mapping of the cards will determine the DSCP values with which the IP packets are marked unless they are changed in the switch.

The 6608 and 6624 will tag packets as follows:

  • COS = 5 for rtp traffic
  • COS = 3 for signalling traffic

By default on the Catalyst 6000, these COS values map in IP packets to DSCP 24 (COS = 3) and 40 (COS = 5) as shown in the table below.

Generally, the recommended DSCP values to use in a VoIP network differ slightly. They are:

  • DSCP = 46 for rtp traffic (Recommended Expedited Forwarding (EF) value)
  • COS = 26 for signalling traffic (AF31)

It may be necessary to change the default COS-DSCP mapping on the Catalyst 6000 so that the DSCP markings in packets generated by the 6608 and 6624 cards conform to the network policy. For example, if other devices in the network are marking packets with the recommended values.

Information on how to change the default COS-DSCP mapping is provided in the Mapping Received CoS Values to Internal DSCP Values section of Catalyst 6000 Family Software Configuration Guide.

In addition, the following service parameters give you the control of the TOS bit marking used by CCM for signalling:

  • IpTosCm2Cm = 3 (default)
  • IpTosCm2Dvce = 3 (default)

Parameter IpTosCm2Dvce controls class of service of IP traffic and signals between Cisco CallManager to device.

Parameter IpTosCm2Cm controls Class of Service for IP traffic and signals between Cisco CallManager to Cisco CallManager.

The following table compares QoS Values for IP Precedence, DSCP, MPLS EXP values along with standard values used in IOS for configuration.

Per Hop Behaviour (PHB)DSCP ValueDSCP BitsIP Precedence and COS Value (xyz000)Comment:MPLX EXP Bits
Default00000000=routine           
  • Best Effort
        
1000001
2000010
3000011
4000100
5000101
6000110
7000111
CS180010001=priority        

        
9001001
AF1110001010           
  • Assured Forwarding Class 1 (001)
  • Drop Priority 010 (1)
  • Dropped last in AF1 Class
        
11001011
AF1212001100           
  • Assured Forwarding Class 1 (001)
  • Drop Priority 100 (2)
  • Dropped 2nd in AF1 Class
        
13001101
AF1314001110           
  • Assured Forwarding Class 1 (001)
  • Drop Priority 110 (3)
  • Dropped first in AF1 Class
        
15001111
CS2160100002=immediate1
17010001
AF2218010010           
  • Assured Forwarding Class 2 (010)
  • Drop Priority 010 (1)
  • Dropped last in AF2 Class
        
18010011
AF2320010100           
  • Assured Forwarding Class 2 (010)
  • Drop Priority 100 (2)
  • Dropped 2nd in AF2 Class
        
21010101
AF2422010110           
  • Assured Forwarding Class 2 (010)
  • Drop Priority 110 (3)
  • Dropped first in AF2 Class
        
23010111
CS3240110003=flash2
25011001
AF3126011010           
  • Assured Forwarding Class 3 (011)
  • Drop Priority 1 (010)
  • Dropped last in AF3 Class
        
27011011
AF3228011100           
  • Assured Forwarding Class 3 (011)
  • Drop Priority 2 (100)
  • Dropped 2nd in AF3 Class
        
29011101
AF3330011110           
  • Assured Forwarding Class 3 (011)
  • Drop Priority 3 (110)
  • Dropped first in AF3 Class
        
31011111
CS4321000004=flashover3
33100001
AF4134100010           
  • Assured Forwarding Class 4 (100)
  • Drop Priority 1 (010)
  • Dropped last in AF4 Class
        
35100011
AF4236100100           
  • Assured Forwarding Class 4 (100)
  • Drop Priority 2 (100)
  • Dropped 2nd in AF4 Class
        
37100101
AF4338100110           
  • Assured Forwarding Class 4 (100)
  • Drop Priority 3 (110)
  • Dropped first in AF4 Class
        
39100111
CS5401010005=critical1
41101001
42101010
43101011
44101100
45101101
EF46101110Recommended Expedited Forwarding (EF) Value (used for voice traffic)6
47101111
CS6481100006=internet0
49110001
50110010
51110011
52110100
53110101
54110110
55110111
CS7561110007=network4
57111001
58111010
59111011
60111100
61111101
62111110
63111111

Version history
Revision #:
1 of 1
Last update:
‎06-22-2009 04:43 PM
Updated by: