Quality of Service CCDA Quick Reference

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

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.

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

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.

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.

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

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.

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

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

Citations Teare, Diane, 2008. Authorized Self-Study Guide: Designing for Cisco Internetwork Solutions (DESIGN), Second Edition. 800 East 96th Street, Indianapolis, Indiana 46240 USA: Cisco Press Cisco Systems, Inc