2 QoS Mechanisms QoS Bandwidth Provisioning Signaling Techniques Classification and MarkingCongestion AvoidanceTraffic Policing and ShapingCongestion ManagementLink Efficiency
3 Bandwidth ProvisionCall Admission Control – provision applications to a certain bandwidth or resource limit so they do not negatively affect other applications.Location-BasedSpecify 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 RSVPApplications 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 TechniquesThe 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 RelayBackward Explicit Congestion NotificationForward 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 classificationClassificationCreated using ACLs, QoS class maps or route maps.Classify based on:ProtocolIngress portIP Precedence or DSCP802.1p Class of Service bitsMarkingMarking is done at L2 or L3Marking is done to reflect the QoS classificationLayer 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 AvoidanceCongestion-Avoidance techniques monitor network traffic loads so that congestion can be anticipated and avoided before it becomes problematic.Random Early DetectionAllows for certain streams to be eligible for early discard.Prevents Congestion before it happensWeighted REDLeverages 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 ShapingTraffic 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 ScopeQueuingHardwareTxQFIFOSoftwareWFQPQCQCBWFQLLQSchedulingScheduling – decides from which queue traffic is to be sent next.
9 Link EfficiencyLink Efficiency reduces unacceptable delays on low-speed links with Link-Fragmentation and Interleaving and Compression schemesLink-Fragmentation and InterleavingVoice 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 schemesCompression 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 ModelCitation for this picture is provided in the next slide
11 CitationsTeare, Diane, Authorized Self-Study Guide: Designing for Cisco Internetwork Solutions (DESIGN), Second Edition East 96th Street, Indianapolis, Indiana USA: Cisco PressCisco Systems, Inc