Quality of Service Ib Hansen ibhansen@cisco.com 1
Why Enable QoS? Security Quality of Service High Availability QoS: Enables UC and other collaborative applications Drives productivity by enhancing service levels to mission-critical applications Cuts costs by bandwidth optimization Helps maintain network availability in the event of DoS/worm attacks 2
Enabling QoS in the Network Traffic Profiles and Requirements Voice Video Data Smooth Bursty Smooth/bursty Benign Greedy Benign/greedy Drop sensitive Drop sensitive Drop insensitive Delay sensitive Delay sensitive Delay insensitive UDP priority UDP priority TCP retransmits Bandwidth per Call Depends on Codec, Sampling-Rate, and Layer 2 Media Latency 150 ms Jitter 30 ms Loss 1% One-Way Requirements Network requirements for video traffic can vary greatly, based on the type of application being used, as well as whether the media flows are standard or high definition. Latency 150 300ms Jitter 10 ms 50ms Loss.05% One-Way Requirements Traffic patterns for Data Vary Among Applications Data Classes: Mission-Critical Apps Transactional/Interactive Apps Bulk Data Apps Best Effort Apps (Default) 3
Typical Voice and Video QoS Requirements Elements that Affect Latency and Jitter PSTN IP WAN Campus Branch Office CODEC Queuing Serialization Propagation and Network Jitter Buffer G.729A: 25 ms Variable Variable Fixed (6.3 µs/km) + Network Delay (Variable) 20 50 ms End-to-End Delay (Must Be 150 ms) 4
What Is Quality of Service? To the End User User s perception that their applications are performing properly Voice No drop calls, no static Video High quality, smooth video Data Rapid response time To the Network Manager Maximize network bandwidth utilization while meeting performance expectations Control Delay The finite amount of time it takes a packet to reach the receiving endpoint Jitter The difference in the end-to-end delay between packets Packet Loss Relative measure of the number of packets that were not received compared to the total number of packets transmitted 5 5
How Is QoS Optimally Deployed? 1. Strategically define the business objectives to be achieved via QoS 2. Analyze the service-level requirements of the various traffic classes to be provisioned for 3. Design and test the QoS policies prior to productionnetwork rollout 4. Roll-out the tested QoS designs to the production-network in phases, during scheduled downtime 5. Monitor service levels to ensure that the QoS objectives are being met 6
Business Objectives 7
New Business Requirements Why Video? 1 Kandola, Pearn The Psychology of Effective Business Communications in Geographically Dispersed Teams, Cisco Systems, September 2006 2 Vision Group Research, FMRIB, University of Oxford, UK 8
New Application Requirements The Impact of HD on the Network User demand for HD video has a major impact on the network (H.264) 720p HD video requires twice as much bandwidth as (H.323) DVD (H.264) 1080p HD video requires twice as much bandwidth as (H.264) 720p 9
How does QOS work? 10
Quality of Service Operations How Does It Work and Essential Elements CLASSIFICATION AND MARKING QUEUEING AND DROPPING POST-QUEUING OPERATIONS Classification and Marking: The first element to a QoS policy is to classify/identify the traffic that is to be treated differently; following classification, marking tools can set an attribute of a frame or packet to a specific value Policing: Determine whether packets are conforming to administratively-defined traffic rates and take action accordingly; such action could include marking, remarking or dropping a packet Scheduling (including Queuing and Dropping): Scheduling tools determine how a frame/packet exits a device; queuing algorithms are activated only when a device is experiencing congestion and are deactivated when the congestion clears Link Specific Mechanisms (Shaping, Fragmentation, Compression, Tx Ring) Offers network administrators tools to optimize link utilization 11
Classification 12
Catalyst 2960/3560/3750 + 3560-E and 3750-E QoS Model Policer Policer Marker Marker Ingress Queues Stack Ring Egress Queues Traffic Classify SRR SRR Policer Marker Ingress Policer Marker Egress Classification Inspect incoming packets Based on ACLs or configuration, determine classification label Policing Ensure conformance to a specified rate On an aggregate or individual flow basis Up to 256 policers per Port ASIC Support for rate and burst Marking Act on policer decision Reclass or drop out-of-profile Ingress Queue/ Schedule Congestion Control Two queues/port ASIC shared servicing One queue is configurable for strict priority servicing WTD for congestion control (three thresholds per queue) SRR is performed Egress Queue/ Schedule Congestion Control Four SRR queues/port shared or shaped servicing One queue is configurable for strict priority servicing WTD for congestion control (three thresholds per queue) Egress queue shaping Egress port rate limiting 13
Classification Tools Layer 2 Ethernet 802.1Q Class of Service Pream. SFD DA Three Bits Used for CoS (802.1p User Priority) SA PRI Type CFI 802.1p user priority field also called Class of Service (CoS) Different types of traffic are assigned different CoS values CoS 6 and 7 are reserved for network use TAG 4 Bytes PT VLAN ID CoS 7 6 5 4 3 2 1 Data 802.1Q/p Header FCS Ethernet Frame Application Reserved Routing Voice Video Call Signaling Critical Data Bulk Data 0 Best Effort Data 14
Classification Tools Layer 3 IP Precedence and DiffServ Code Points Version Length ToS Byte Len ID Offset TTL Proto FCS IP SA IP DA Data IPv4 Packet 7 6 5 4 3 2 1 0 IP Precedence Unused DiffServ Code Point (DSCP) IP ECN Standard IPv4 DiffServ Extensions IPv4: Three most significant bits of ToS byte are called IP Precedence (IPP) other bits unused DiffServ: Six most significant bits of ToS byte are called DiffServ Code Point (DSCP) remaining two bits used for flow control DSCP is backward-compatible with IP precedence 15
Classification Tools MPLS EXP Bits Frame Encapsulation MPLS Shim Header Label Stack Label Header Layer-2 Header Label Header 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 Label EXP S TTL Payload 3 2 1 0 MPLS EXP S Packet Class and drop precedence inferred from EXP (three-bit) field RFC3270 does not recommend specific EXP values for DiffServ PHB (EF/AF/DF) Used for frame-based MPLS 16
Scheduling 17
Scheduling Tools Queuing Algorithms Voice Video 1 1 2 2 3 3 Data Congestion can occur at any point in the network where there are speed mismatches Routers use Cisco IOS -based software queuing Low-Latency Queuing (LLQ) used for highest-priority traffic (voice/video) Class-Based Weighted-Fair Queuing (CBWFQ) used for guaranteeing bandwidth to data applications Cisco Catalyst switches use hardware queuing 18
Scheduling Tools LLQ/CBWFQ Subsystems Low Latency Queueing Police VoIP IP/VC PQ Link Fragmentation and Interleave Packets In Signaling Critical Bulk CBWFQ Fragment Interleave TX Ring Packets Out Mgmt FQ Default Layer 3 Queueing Subsystem Layer 2 Queueing Subsystem 19
Scheduling Tools Congestion Avoidance Algorithms TAIL DROP WRED Queue 3 31 01 2 1 2 0 2 0 3 2 1 3 0 3 Queueing algorithms manage the front of the queue which packets 3 get transmitted first 0 Congestion avoidance algorithms manage the tail of the queue which packets get dropped first when queuing buffers fill Weighted Random Early Detection (WRED) WRED can operate in a DiffServ-compliant mode Drops packets according to their DSCP markings WRED works best with TCP-based applications, like data 20
Link specific tools 21
Link-Specific Tools Link-Fragmentation and Interleaving Serialization Can Cause Excessive Delay Voice Data Data Data Data Voice Data With Fragmentation and Interleaving Serialization Delay Is Minimized Serialization delay is the finite amount of time required to put frames on a wire For links 768 kbps serialization delay is a major factor affecting latency and jitter For such slow links, large data packets need to be fragmented and interleaved with smaller, more urgent voice packets 22
Link-Specific Tools IP RTP Header Compression IP Header 20 Bytes UDP Header 8 Bytes RTP Header 12 Bytes Voice Payload crtp Reduces L3 VoIP BW by: ~ 20% for G.711 ~ 60% for G.729 2 5 Bytes 23
QOS Requirements 24
QoS and IPSEC QOS when using the Internet as transport = IPsec tunnels Rate: 8Mbps / 768 Kbps ADSL IPSec Tunnel Rate: 100 Mbps Leased line Internet QOS End End QOS not possible QOS possible at each end of tunnel Internet service provider routers typically not QOS enabled 25
Networks that supports end to end QOS Leased Lines MPLS CE Router PE Router MPLS VPN PE Router CE Router P Routers MPLS best price / perfomance 26
Voice QoS Requirements End-to-End Latency Avoid the Human Ethernet Hello? Hello? Satellite Quality CB Zone High Quality Fax Relay, Broadcast 0 100 200 300 400 500 600 700 800 Time (msec) Delay Target ITU s G.114 Recommendation: 150msec One-Way Delay 27
Voice QoS Requirements Elements that Affect Latency and Jitter PSTN IP WAN Campus Branch Office CODEC Queuing Serialization Propagation and Network Jitter Buffer G.729A: 25 ms Variable Variable Fixed (6.3 µs/km) + Network Delay (Variable) 20 50 ms End-to-End Delay (Must Be 150 ms) 28
Voice QoS Requirements Packet Loss Limitations Voice Voice Voice Voice Voice Voice Voice Voice 4 3 2 1 4 3 2 1 Voice 3 Voice 3 Reconstructed Voice Sample Cisco DSP codecs can use predictor algorithms to compensate for a single lost packet in a row Two lost packets in a row will cause an audible clip in the conversation 29
Voice QoS Requirements Provisioning for Voice Latency 150 ms Jitter 30 ms Loss 1% 17 106 kbps guaranteed priority bandwidth per call One-Way Requirements Voice 150 bps (+ Layer 2 overhead) guaranteed bandwidth for Voice-Control traffic per call CAC must be enabled Smooth Benign Drop sensitive Delay sensitive UDP priority 30
Video QoS Requirements Provisioning for Interactive Video Latency 150 300ms Jitter 10 50ms Loss.05% Minimum priority bandwidth guarantee required is: Video-stream + 10 20% e.g., a 384 kbps stream could require up to 460 kbps of priority bandwidth CAC must be enabled One-Way Requirements Video Bursty Drop sensitive Delay sensitive UDP priority 31
QoS Tools Mapped to Design Requirements PSTN Campus IP WAN Bandwidth Provisioning SRST router Branch Office Campus Access Campus Distribution WAN Aggregator Branch Router Branch Switch Inline Power Multiple Queues 802.1Q/p DSCP Fast link convergence Multiple Queues 802.1Q/p DSCP LLQ CBWFQ WRED LFI/FRF.12 crtp FRTS, dts H-Shaping LLQ CBWFQ WRED LFI/FRF.12 crtp FRTS NBAR H-Shaping Inline Power Multiple Queues 802.1Q/p 32
What Is the Challenge? Baseline Challenge: Know how much traffic is flowing, what and where Deployment Challenge: QoS policies are difficult to configure and scale in a consistent end-to-end manner Operations Challenge: The lack of QoS operational visibility to evaluate the effectiveness and validate results 33
34