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Catalyst 3750 Metro Switch Software Configuration Guide
78-15870-01
Chapter 1 Overview
Features
QoS Features
• Standard QoS to classify, police, mark, queue, and schedule incoming traffic on a standard port or
on an ES port, as well as queue and schedule outgoing traffic on a standard port
Classification
–
IP type-of-service/Differentiated Services Code Point (IP ToS/DSCP) and 802.1p CoS marking
priorities on a per-port basis for protecting the performance of mission-critical applications
–
IP ToS/DSCP and 802.1p CoS marking based on flow-based packet classification (classification
based on information in the MAC, IP, and TCP/UDP headers) for high-performance quality of
service at the network edge, allowing for differentiated service levels for different types of
network traffic and for prioritizing mission-critical traffic in the network
–
Trusted port states (CoS, DSCP, and IP precedence) within a QoS domain and with a port
bordering another QoS domain
–
Trusted boundary for detecting the presence of a Cisco IP phone, trusting the CoS value
received, and ensuring port security
Policing and out-of-profile marking
–
Traffic-policing policies on the switch port for managing how much of the port bandwidth
should be allocated to a specific traffic flow (single-rate traffic policing)
–
Aggregate policing for policing traffic flows in aggregate to restrict specific applications or
traffic flows to metered, predefined rates
–
Out-of-profile markdown for packets that exceed bandwidth utilization limits (drop policy
actions are passing through the packet without modification, marking down the assigned DSCP
in the packet, or dropping the packet)
Ingress queueing and scheduling
–
Two configurable ingress queues for user traffic (one queue can be the priority queue)
–
Weighted tail drop (WTD) as the congestion-avoidance mechanism for managing the queue
lengths and providing drop precedences for different traffic classifications
–
Shaped round robin (SRR) as the scheduling service for determining the rate at which packets
are dequeued to the internal ring (sharing is the only supported mode on ingress queues)
Egress queues and scheduling
–
Four egress queues per port
–
WTD as the congestion-avoidance mechanism for managing the queue lengths and providing
drop precedences for different traffic classifications
–
SRR as the scheduling service for determining the rate at which packets are dequeued to the
egress interface (shaping or sharing is supported on egress queues). Shaped egress queues are
guaranteed but limited to using a share of port bandwidth. Shared egress queues are also
guaranteed a configured share of bandwidth, but can use more than the guarantee if other queues
become empty and do not use their share of the bandwidth.
• Hierarchical QoS on ES ports to classify, police, mark, queue, and schedule outgoing traffic
Classification
–
Three QoS configuration levels in the hierarchy: class, VLAN, and physical interface
–
Classification based on the CoS value, the DSCP value, the IP precedence value, the MPLS
experimental (EXP) bits, or the VLAN
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