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Cisco AVVID Network Infrastructure Enterprise Quality of Service Design
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Chapter 2 QoS Considerations When Connecting End-Points to an AVVID Network
Video
VoIP Gateways
Cisco offers two types of VoIP gateways: H.323 and MGCP.
H.323
IOS-based H.323 gateways can be configured to correctly mark their VoIP bearer traffic with a DSCP
value of EF and their VoIP control traffic with a DSCP value of AF31.
Tip
Detailed examples for IOS configurations can be found in the IP Telephony QoS Design Guide.
Because H.323 gateways correctly mark their traffic, the network requirement at the trusted edge is to
allow the classified traffic to be admitted to the network. This is accomplished through the use of the
trust dscp
or trust ip precedence port/interface level configuration command.
MGCP
MGCP gateways can be configured to correctly mark their VoIP bearer traffic with a DSCP value of EF
and their VoIP control traffic with a DSCP value of AF31.
Tip
Detailed examples for IOS configurations can be found in the IP Telephony QoS Design Guide.
Because MGCP gateways correctly mark their traffic, the network requirement at the trusted edge is to
allow the classified traffic to be admitted to the network. This is accomplished through the use of the
trust dscp
or trust ip precedence port/interface level configuration command.
Classification for Non-marking Applications
Some Cisco applications and older versions of IOS-based gateways may not correctly classify their VoIP
bearer and control traffic. When this is the case, the requirement at the trusted edge of the network is to
apply the correct classification. Because these devices generate both VoIP control and bearer traffic, you
cannot use the simple port-level configuration commands to set the CoS or DSCP. In this case, a Layer 3
aware switch that supports Modular Quality of Service CLI (MQC)-based classification should be used.
When you use MQC, the VoIP bearer and control traffic is identified via extended Access Control Lists
(ACLs) and subsequently marked with the correct DSCP value (EF for VoIP bearer and AF31 for VoIP
control). Configuration examples using MQC are included in
Chapter 3, "QoS in an AVVID-Enabled
Campus Network"
and
Chapter 4, "QoS in an AVVID-Enabled Wide-Area Network."
Video
There are two types of IP Video traffic: IP video conferencing, which is an interactive, two-way video,
and streaming video, which is one way, view only. Each has different and specific requirements of the
network. One varies greatly in its bandwidth and packet size requirements and is very delay and delay
variation sensitive, while the other acts very much like a large file transfer (tolerant of delay, delay