QoS

Key QoS requirements and recommendations for call signaling traffic:

• Call signaling traffic should be marked as DSCP CS3 per the QoS Baseline (it can also be marked with the legacy value of DSCP AF31).
• 150 bps (plus Layer 2 overhead) per phone of guaranteed bandwidth is required for voice control traffic; more may be required, depending on the call signaling protocol.

References

Cisco QoS Exam Certification Guide (IP Telephony Self-Study) (2nd Edition)
End-to-End QoS Network Design: Quality of Service in LANs, WANs, and VPNs

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Key QoS requirements and recommendations for voice (bearer traffic):

• Voice traffic should be marked to DSCP EF per the QoS Baseline and RFC 3246.
• Loss should be no more  than 1 percent.
• One-way latency (mouth to ear) should be no more than 150 ms.
• Average one-way jitter should be targeted at less than 30 ms.
• A range of 21 to 320 Kbps of guaranteed priority bandwidth is required per call (depending on the sampling rate, the VoIP codec, and Layer 2 media overhead).

Reference

End-To-End QoS Network Design: Quality of Service in LANs, WANs, and VPNs

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There are three main components that make up the MQC (Modular QoS CLI) and are listed below:

• class-map – This is used as a classification filter defined within the policy map to identify traffic for preferential or deferential treatment. Traffic can be identified by IPP or DSCP, named or numbered ACL, Network-Based Application Recognition (NBAR), Layer 2 parameters (CoS, FR DE, ATM cell loss priority [CLP], MPLS Experimental [EXP] value), or combination of all of these.
• policy-map – This is used as a statement that defines how each traffic type, as identified by the class map(s), should be serviced. Options include marking/re-marking, policing, shaping, low-latency or class-based weighted fair queuing, selective dropping, and header compression.
• service-policy – This is used as a statement that binds the policy to an interface and specifies direction

For example:

ip access-list extended VOICE-RTP
 permit udp 192.168.1.0 0.0.0.255 any range 16384 32767
ip access-list extended VOICE-SIGNALING
 permit tcp 192.168.1.0 0.0.0.255 any range 2000 2002
!
class-map match-all VOICE-SIGNALING
 match access-group name VOICE-SIGNALING
class-map match-all VOICE-RTP
 match access-group name VOICE-RTP
!
policy-map VOICE
 class VOICE-RTP
 set dscp ef
 class VOICE-SIGNALING
 set dscp cs3
!
interface Vlan10
 description Voice VLAN
 service-policy input VOICE
!
end

References

Cisco QoS Exam Certification Guide (IP Telephony Self-Study) (2nd Edition)
End-to-End QoS Network Design: Quality of Service in LANs, WANs, and VPNs

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Cisco QoS tools fall into these categories:

• Classification and marking tools
• Policing and shaping tools
• Congestion-avoidance (selective dropping) tools
• Congestion-management (queuing) tools
• Link-specific tools

Click here for more information.

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According to End-To-End QoS Network Design: Quality of Service in LANs, WANs, and VPNs book, there are four available standard PHBs (Per-Hop Behavior) and are listed below:

• Expedited Forwarding (EF) – Provides a strict-priority service. This is similar to the Express Mail service of USPS.
• Assured Forwarding (AF) – Provides a qualified delivery guaranteee and makes the provision for oversubscription to this service (specifically, markdown and dropping schemes for excess traffic). This is similar to Registered Mail service of USPS.
• Class Selectors (CS) – Provides code points that can be used for backward compatibility with IP Precedence models.
• Default PHB (Best-Effort Service) – Provides a “delivery when possible” or best effort service. This is similar to Regular Mail service of USPS.

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Reference

End-To-End QoS Network Design: Quality of Service in LANs, WANs, and VPNs

Disclosure

NetworkJutsu.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.