© 2005 Cisco Systems, Inc. All rights reserved. IPTX v Introduction to IP Quality of Service Quality of Service
© 2005 Cisco Systems, Inc. All rights reserved. IPTX v Outline Overview Quality of Service Defined Converged Networks Converged Networks Quality Issues Bandwidth End to End Delay Packet Loss QoS Requirements QoS Policy QoS for Converged Networks LAN QoS Considerations Summary
© 2005 Cisco Systems, Inc. All rights reserved. IPTX v Quality of Service Defined
© 2005 Cisco Systems, Inc. All rights reserved. IPTX v Converged Networks: Network Before Convergence Traditional data traffic characteristics: Bursty data flow First-come, first-served access Mostly not time sensitive – delays OK Brief outages are survivable
© 2005 Cisco Systems, Inc. All rights reserved. IPTX v Converged Networks: Network After Convergence Converged traffic characteristics: Constant small packet voice flow competes with with bursty data flow Critical traffic must get priority Voice and video are time sensitive Brief outages not acceptable
© 2005 Cisco Systems, Inc. All rights reserved. IPTX v Converged Networks: Quality Issues Phone Call: I cant understand you; your voice is breaking up Teleconferencing: The picture is very jerky. Voice not synchronized. Brokerage House: I needed that information 2 hours ago. Where is it? Call Center: Please hold while my screen refreshes.
© 2005 Cisco Systems, Inc. All rights reserved. IPTX v Converged Networks: Quality Issues (Cont.) Lack of bandwidth: multiple flows compete for a limited amount of bandwidth End-to-end delay (fixed and variable): packets have to traverse many network devices and links that add up to the overall delay Variation of delay (jitter): sometimes there is a lot of other traffic which results in more delay Packet Loss: packets may have to be dropped when a link is congested
© 2005 Cisco Systems, Inc. All rights reserved. IPTX v Lack of Bandwidth Maximum available bandwidth equals the bandwidth of the weakest link Multiple flows are competing for the same bandwidth resulting in much less bandwidth being available to one single application BW max = min(10M, 256k, 512k, 100M)=256kbps BW avail = BW max /Flows Bad Voice Due to Lack of BW
© 2005 Cisco Systems, Inc. All rights reserved. IPTX v Ways to Increase Available Bandwidth
© 2005 Cisco Systems, Inc. All rights reserved. IPTX v Ways to Increase Available Bandwidth (Cont.)
© 2005 Cisco Systems, Inc. All rights reserved. IPTX v Ways to Increase Available Bandwidth (Cont.)
© 2005 Cisco Systems, Inc. All rights reserved. IPTX v Ways to Increase Available Bandwidth (Cont.)
© 2005 Cisco Systems, Inc. All rights reserved. IPTX v Ways to Increase Available Bandwidth (Cont.)
© 2005 Cisco Systems, Inc. All rights reserved. IPTX v Ways to Increase Available Bandwidth
© 2005 Cisco Systems, Inc. All rights reserved. IPTX v End-to-End Delay End-to-end delay equals a sum of all propagation, processing and queuing delays in the path Propagation delay is fixed, processing and queuing delays are unpredictable in best-effort networks Delay = P1 + Q1 + P2 + Q2 + P3 + Q3 + P4 = X ms Bad Voice Due to Delay Variation
© 2005 Cisco Systems, Inc. All rights reserved. IPTX v Processing and Queuing Delay Processing Delay: the time it takes for a router to take the packet from an input interface, examine it, and put it into the output queue of the output interface Queuing Delay: the time a packets resides in the output queue of a router Serialization Delay: the time it takes to place the bits on the wire Propagation Delay: the time it takes to transmit a packet
© 2005 Cisco Systems, Inc. All rights reserved. IPTX v Processing and Queuing Delay (Cont.) Processing Delay: the time it takes for a router to take the packet from an input interface, examine it, and put it into the output queue of the output interface Queuing Delay: the time a packets resides in the output queue of a router Serialization Delay: the time it takes to place the bits on the wire Propagation Delay: the time it takes to transmit a packet
© 2005 Cisco Systems, Inc. All rights reserved. IPTX v Processing and Queuing Delay Processing Delay: the time it takes for a router to take the packet from an input interface, examine it, and put it into the output queue of the output interface Queuing Delay: the time a packets resides in the output queue of a router Serialization Delay: the time it takes to place the bits on the wire Propagation Delay: the time it takes to transmit a packet
© 2005 Cisco Systems, Inc. All rights reserved. IPTX v Ways to Reduce Delay
© 2005 Cisco Systems, Inc. All rights reserved. IPTX v Ways to Reduce Delay (Cont.)
© 2005 Cisco Systems, Inc. All rights reserved. IPTX v Ways to Reduce Delay (Cont.)
© 2005 Cisco Systems, Inc. All rights reserved. IPTX v Ways to Reduce Delay (Cont.)
© 2005 Cisco Systems, Inc. All rights reserved. IPTX v Ways to Reduce Delay (Cont.)
© 2005 Cisco Systems, Inc. All rights reserved. IPTX v Ways to Reduce Delay
© 2005 Cisco Systems, Inc. All rights reserved. IPTX v Packet Loss Tail-drops occur when the output queue is full. These are common drops which happen when a link is congested Many other types of drops exist, usually the result of router congestion, that are uncommon and may require a hardware upgrade (input drop, ignore, overrun, frame errors) Bad Voice Due to Packet Loss
© 2005 Cisco Systems, Inc. All rights reserved. IPTX v Ways to Prevent Packet Loss
© 2005 Cisco Systems, Inc. All rights reserved. IPTX v Ways to Prevent Packet Loss (Cont.)
© 2005 Cisco Systems, Inc. All rights reserved. IPTX v Ways to Prevent Packet Loss (Cont.)
© 2005 Cisco Systems, Inc. All rights reserved. IPTX v Ways to Prevent Packet Loss (Cont.)
© 2005 Cisco Systems, Inc. All rights reserved. IPTX v Ways to Prevent Packet Loss
© 2005 Cisco Systems, Inc. All rights reserved. IPTX v QoS Traffic Requirements: Voice Latency < 150 ms* Jitter < 30 ms* Loss < 1%* kbps guaranteed priority bandwidth per call 150 bps (+ layer 2 overhead) guaranteed bandwidth for Voice- Control traffic per call * one-way requirements – – –
© 2005 Cisco Systems, Inc. All rights reserved. IPTX v QoS Traffic Requirements: Video-Conferencing Latency < 150 ms Jitter < 30 ms Loss < 1% Minimum priority bandwidth guarantee required is: –Video-Stream + 20% –e.g. a 384 kbps stream would require 460 kbps of priority bandwidth * one-way requirements – – –
© 2005 Cisco Systems, Inc. All rights reserved. IPTX v QoS Traffic Requirements: Data Different applications have different traffic characteristics Different versions of the same application can have different traffic characteristics Classify Data into relative-priority model with no more than four to five classes: –Mission-Critical Apps: Locally defined critical applications –Transactional: Interactive traffic, preferred data service –Best-Effort: Internet, , Unspecified traffic –Less-Than-Best-Effort (Scavenger): Napster / Kazaa, peer-to-peer applications
© 2005 Cisco Systems, Inc. All rights reserved. IPTX v QoS Policy A network-wide definition of the specific levels of quality of service assigned to different classes of network traffic
© 2005 Cisco Systems, Inc. All rights reserved. IPTX v QoS Policy (Cont.) Align Network Resources with Business Priorities
© 2005 Cisco Systems, Inc. All rights reserved. IPTX v Step 1: Identify Traffic and its Requirements Network audit –Identify traffic on the network Business audit –Determine how each type of traffic is important for business Service levels required –Determine required response time
© 2005 Cisco Systems, Inc. All rights reserved. IPTX v Step 2: Divide the Traffic into Service Classes
© 2005 Cisco Systems, Inc. All rights reserved. IPTX v Step 3: Define Policies for Each Service Class Set minimum bandwidth guarantee Set maximum bandwidth limits Assign priorities to each class Manage congestion
© 2005 Cisco Systems, Inc. All rights reserved. IPTX v LAN QoS Considerations Bandwidth typically not an issue Buffer congestion is an issue Buffer congestion occurs when there is a rate change or if many interfaces are aggregated to a single uplink
© 2005 Cisco Systems, Inc. All rights reserved. IPTX v Summary Quality of Service (QoS) is the ability of the network to provide better or special service to users/applications. Converged networks create new requirements for managing network traffic. Converged networks suffer from different quality issues including, lack of adequate bandwidth, end-to-end and variable delay, and lost packets. Many technologies exist today which can overcome the problems presented by lack of bandwidth, delay, variable delay, and packet loss.
© 2005 Cisco Systems, Inc. All rights reserved. IPTX v Summary (Cont.) Voice, video, and data have very different quality of service requirements to run effectively on a network A QoS Policy is a network-wide definition of the specific levels of quality of service assigned to classes of network traffic Building Quality of Service requires three steps: identify requirements, classify network traffic, and define network-wide policies for quality