1. Quality of Service
CCDA Quick Reference

2. QoS Mechanisms QoS Bandwidth Provisioning Signaling Techniques
Classification and Marking
Congestion Avoidance
Traffic Policing and Shaping
Congestion Management
Link Efficiency

3. Bandwidth Provision
Call Admission Control – provision applications to a certain bandwidth or resource limit so they do not negatively affect other applications.
Location-Based
Specify the maximum bandwidth available for calls to and from each location.
Limits the number of active calls and preventing the WAN from be oversubscribed.
Hub-and-spoke design only.
CAC with RSVP
Applications must first request to reserve bandwidth.
RSVP defines signaling messages that are exchanged between the source and destination devices for the data flow and that are processed by intermediate routers along the path.

4. Signaling Techniques
The Resource Reservation Protocol (RSVP) allows bandwidth and other resources along the routing path to be reserved so that a certain level of quality is provided for delay-sensitive traffic.
Frame Relay
Backward Explicit Congestion Notification
Forward Explicit Congestion Notification

5. Classification and Marking
Classification is the process of partitioning traffic into multiple priority levels or classes of service.
Marking is the process of changing the priority of class of service setting within a frame or packet to indicate its classification
Classification
Created using ACLs, QoS class maps or route maps.
Classify based on:
Protocol
Ingress port
IP Precedence or DSCP
802.1p Class of Service bits
Marking
Marking is done at L2 or L3
Marking is done to reflect the QoS classification
Layer 3 marking changes the IP Precedence or DSCP values in the IP packet.
Layer 2 marking changes the Class of Service bits in the 802.1Q frame.

6. Random Early Detection
Congestion Avoidance
Congestion-Avoidance techniques monitor network traffic loads so that congestion can be anticipated and avoided before it becomes problematic.
Random Early Detection
Allows for certain streams to be eligible for early discard.
Prevents Congestion before it happens
Weighted RED
Leverages RED by also using IP Precedence and DSCP values to determine which streams to initiate discarding.

7. Traffic Policing and Shaping
Traffic policing either discards the packet or modifies some aspect of it, such as its IP Precedence of CoS bits, when the policing agent determines that the packet that the packet meets a given criterion.
Traffic Shaping
Traffic shaping attempts to adjust the transmission rate of packets that match a certain criterion. A shaper typically delays excess traffic by using a buffer or queuing mechanism to hold packets and shape the flow when the source’s data rate is higher than expected

8. Congestion Management
Congestion Management Scope
Queuing
Hardware
TxQ
FIFO
Software
WFQ PQ CQ
CBWFQ
LLQ
Scheduling
Scheduling – decides from which queue traffic is to be sent next.

9. Link Efficiency
Link Efficiency reduces unacceptable delays on low-speed links with Link-Fragmentation and Interleaving and Compression schemes
Link-Fragmentation and Interleaving
Voice gateway fragments large packets into smaller equal-sized frames and interleaves them with small voice packets.
A voice packet does not have to wait until the entire large data packet is sent. LFI reduces and ensures a more predictable voice delay.
Compression schemes
Compression is the reduction of data size to save transmission time.
Compression enables more efficient use of the available bandwidth, which is often limited.
Compression algorithms include: FRF.9, LZS (STC), Predictor, etc…
cRTP for compression of IP/UDP/RTP header

10. Layered QoS Model
Citation for this picture is provided in the next slide

11. Citations
Teare, Diane, Authorized Self-Study Guide: Designing for Cisco Internetwork Solutions (DESIGN), Second Edition East 96th Street, Indianapolis, Indiana USA: Cisco Press
Cisco Systems, Inc