Just a brief note to mention QoS for call control and media flow on ISRs. Three areas are Dial Peers, MGCP Gateways (IOS Only) and SCCP controlled resources. Its important to understand where to find the QoS related configuration for each of the above not only for the CCIE Voice exam but for real-world projects aswell.

Dial-Peers

The default QoS markings are the same for both H323 (Default) and SIP dialpeers on an ISR. The RTP or Media is marked as EF, while the Signalling is marked at AF31. Remember Industry best practices for RTP/Media is EF and for signalling is CS3. To find this information on a Cisco ISR, enter the following command.

#Show dial-peer voice dialpeer number | i DSCP

Output from the above command:

ip media DSCP = ef, ip media rsvp-pass DSCP = ef
ip media rsvp-fail DSCP = ef, ip signaling DSCP = af31,
ip video rsvp-none DSCP = af41,ip video rsvp-pass DSCP = af41
ip video rsvp-fail DSCP = af41,

To change the default QoS markings, entering the Dial-Peer config mode and use the below commands:

• ip qos dscp ef media
• ip qos dscp cs3 signalling

I realise we are not changing the EF marking, but this is just to give you an example of where and how to change the markings.

You can find all the QoS DSCP Values and their relating Binary numbers if enter the ? after dscp:

(config-dial-peer)# ip qos dscp ?

<0-63>   DSCP value
af11     Sets DSCP to assured forwarding (af11) bit pattern 001010
af12     Sets DSCP to assured forwarding (af12) bit pattern 001100
af13     Sets DSCP to assured forwarding (af13) bit pattern 001110
af21     Sets DSCP to assured forwarding (af21) bit pattern 010010
af22     Sets DSCP to assured forwarding (af22) bit pattern 010100
af23     Sets DSCP to assured forwarding (af23) bit pattern 010110
af31     Sets DSCP to assured forwarding (af31) bit pattern 011010
af32     Sets DSCP to assured forwarding (af32) bit pattern 011100
af33     Sets DSCP to assured forwarding (af33) bit pattern 011110
af41     Sets DSCP to assured forwarding (af41) bit pattern 100010
af42     Sets DSCP to assured forwarding (af42) bit pattern 100100
af43     Sets DSCP to assured forwarding (af43) bit pattern 100110
cs1      Sets DSCP to class selector codepoint 1 (precedence 1)
cs2      Sets DSCP to class selector codepoint 2 (precedence 2)
cs3      Sets DSCP to class selector codepoint 3 (precedence 3)
cs4      Sets DSCP to class selector codepoint 4 (precedence 4)
cs5      Sets DSCP to class selector codepoint 5 (precedence 5)
cs6      Sets DSCP to class selector codepoint 6 (precedence 6)
cs7      Sets DSCP to class selector codepoint 7 (precedence 7)
default  Sets DSCP to default bit pattern of 000000
ef       Sets DSCP to expedited forwarding bit pattern 101110

MGCP Controlled Resources

MGCP has the same defaults as Dial Peers, so I won’t go in too deep. To find the what QoS values have been configured for MGCP resources enter the command:

#Show mgcp | i DSCP

To change the DSCP Values for media and signalling in MGCP, enter the following commands:

(config)#mgcp ip qos dscp ef media

(config)#mgcp ip qos dscp cs3 signalling

SCCP Controlled Resources

QoS default markings for SCCP are EF for RTP/Media and CS3 for signalling, so in effect SCCP meets the industry best practices. However dont assume these values are configured correctly for the CCIE Voice lab exam. SCCP QoS config is found in the SCCP CCM Group configuration.

#Show sccp ccm group 1

To configure QoS markings for SCCP CCM Groups enter the following:

(config-sccp-ccm)#audio dscp ef

(config-sccp-ccm)#signalling dscp cs3

I hope this clarifies a little for you, now knowing exactly where to go find and change DSCP Values for call controll resources on an ISR Voice Gateway.