Information Technology Reference
In-Depth Information
If multiple classes are configured for LLQ, they share a single queue but are allocated
bandwidth and policed individually. It is recommended that you place only voice in the
priority queue, because voice traffic typically is well behaved, requiring fixed maximum
amounts of bandwidth per call. The voice traffic is identified by IP precedence bits set to a
value of 5 or a DSCP of Expedited Forwarding (EF) with values of 101xxx. Introducing
video or other variable-rate, real-time or non-real-time traffic types could cause unaccept-
able jitter for the voice traffic. Video traffic normally is set to AF41 (100010). And signal-
ing normally is set to an IP precedence of 3 or a DSCP of 011xxx.
Auto QoS
Auto QoS is a Cisco IOS feature that uses a simpler command-line interface (CLI) to en-
able QoS for VoIP in WAN and LAN environments. Auto QoS significantly reduces the
number of configuration lines necessary to support VoIP in the network.
For the WAN, Auto QoS prov ides the follow ing c apabilities:
Automatically classifies RTP and VoIP control packets
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Builds VoIP Modular QoS in the Cisco IOS software
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Provides LLQ for VoIP bearer traffic
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Provides minimum-bandwidth guarantees by using CBWFQ for VoIP control traffic
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For the L AN, Auto QoS prov ides the follow ing c apabilities:
Enforces a trust boundary at the Cisco IP phone
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Enforces a trust boundary on the Catalyst switch access and uplink and downlink ports
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Enables strict-priority queuing and weighted round robin for voice and data traffic
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Modifies queue admission criteria by performing CoS-to-queue mapping
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Modifies queue sizes and queue weights where required
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Modifies CoS-to-DSCP and IP precedence-to-DSCP mappings
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AutoQoS is beneficial for small and medium-size businesses that need to deploy IPT
quickly but lack the experience and staffing to plan and deploy IP QoS services.
AutoQoS also benefits large customer enterprises that need to deploy Cisco IPT on a
large scale while reducing the costs, complexity, and timeframe for deployment and ensur-
ing that the appropriate QoS for voice applications is being set consistently.
Ta ble 1 4 -1 4 summarizes QoS schemes used with IPT.
Ta b l e 1 4 -1 4
QoS Scheme Summary
QoS
Scheme
Description
cRTP
bytes.
