QOS Lecture 4 Introducing QOS 2006 Cisco Systems

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QOS Lecture 4 - Introducing QOS © 2006 Cisco Systems, Inc. All rights reserved.

QOS Lecture 4 - Introducing QOS © 2006 Cisco Systems, Inc. All rights reserved.

Objectives § Explain why converged networks require Qo. S. § Identify the major quality

Objectives § Explain why converged networks require Qo. S. § Identify the major quality issues with converged networks. § Calculate available bandwidth given multiple flows. § Describe mechanisms designed to use bandwidth more efficiently. § Describe types of delay. § Identify ways to reduce the impact of delay on quality. § Describe packet loss and ways to prevent or reduce packet loss in the network. © 2006 Cisco Systems, Inc. All rights reserved.

Traditional Nonconverged Network § Traditional data traffic characteristics: Bursty data flow FIFO access Not

Traditional Nonconverged Network § Traditional data traffic characteristics: Bursty data flow FIFO access Not overly time-sensitive; delays OK Brief outages are survivable © 2006 Cisco Systems, Inc. All rights reserved.

Converged Network Realities § Converged network realities: Constant small-packet voice flow competes with bursty

Converged Network Realities § Converged network realities: Constant small-packet voice flow competes with bursty data flow. Critical traffic must have priority. Voice and video are time-sensitive. Brief outages are not acceptable. © 2006 Cisco Systems, Inc. All rights reserved.

Converged Network Quality Issues § Lack of bandwidth: Multiple flows compete for a limited

Converged Network Quality Issues § 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; this travel adds up to the overall delay. § Variation of delay (jitter): Sometimes there is a lot of other traffic, which results in varied and increased delay. § Packet loss: Packets may have to be dropped when a link is congested. © 2006 Cisco Systems, Inc. All rights reserved.

Measuring Available Bandwidth § The maximum available bandwidth is the bandwidth of the slowest

Measuring Available Bandwidth § The maximum available bandwidth is the bandwidth of the slowest link. § Multiple flows are competing for the same bandwidth, resulting in much less bandwidth being available to one single application. § A lack in bandwidth can have performance impacts on network applications. © 2006 Cisco Systems, Inc. All rights reserved.

Increasing Available Bandwidth § § Upgrade the link (the best but also the most

Increasing Available Bandwidth § § Upgrade the link (the best but also the most expensive solution). Improve Qo. S with advanced queuing mechanisms to forward the important packets first. Compress the payload of Layer 2 frames (takes time). Compress IP packet headers. © 2006 Cisco Systems, Inc. All rights reserved.

Using Available Bandwidth Efficiently Voice 1 1 2 2 3 3 3 4 4

Using Available Bandwidth Efficiently Voice 1 1 2 2 3 3 3 4 4 4 (Highest) Data (High) Data (Medium) Data (Low) 4 Voice • LLQ • RTP header compression 4 3 2 1 1 Data • CBWFQ • TCP header compression § Using advanced queuing and header compression mechanisms, the available bandwidth can be used more efficiently: Voice: LLQ and RTP header compression Interactive traffic: CBWFQ and TCP header compression © 2006 Cisco Systems, Inc. All rights reserved.

Types of Delay § Processing delay: The time it takes for a router to

Types of Delay § Processing delay: The time it takes for a router to take the packet from an input interface, examine the packet, and put the packet into the output queue of the output interface. § Queuing delay: The time a packet 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 for the packet to cross the link from one end to the other. © 2006 Cisco Systems, Inc. All rights reserved.

The Impact of Delay and Jitter on Quality § End-to-end delay: The sum of

The Impact of Delay and Jitter on Quality § End-to-end delay: The sum of all propagation, processing, serialization, and queuing delays in the path § Jitter: The variation in the delay. § In best-effort networks, propagation and serialization delays are fixed, while processing and queuing delays are unpredictable. © 2006 Cisco Systems, Inc. All rights reserved.

Ways to Reduce Delay § § § Upgrade the link (the best solution but

Ways to Reduce Delay § § § Upgrade the link (the best solution but also the most expensive). Forward the important packets first. Enable reprioritization of important packets. Compress the payload of Layer 2 frames (takes time). Compress IP packet headers. © 2006 Cisco Systems, Inc. All rights reserved.

Reducing Delay in a Network § Customer routers perform: TCP/RTP header compression LLQ Prioritization

Reducing Delay in a Network § Customer routers perform: TCP/RTP header compression LLQ Prioritization § ISP routers perform: Reprioritization according to the Qo. S policy © 2006 Cisco Systems, Inc. All rights reserved.

The Impacts of Packet Loss § Telephone call: “I cannot understand you. Your voice

The Impacts of Packet Loss § Telephone call: “I cannot understand you. Your voice is breaking up. ” § Teleconferencing: “The picture is very jerky. Voice is not synchronized. ” § Publishing company: “This file is corrupted. ” § Call center: “Please hold while my screen refreshes. ” © 2006 Cisco Systems, Inc. All rights reserved.

Types of Packet Drops § Tail drops occur when the output queue is full.

Types of Packet Drops § Tail drops occur when the output queue is full. Tail drops are common and happen when a link is congested. § Other types of drops, usually resulting from router congestion, include input drop, ignore, overrun, and frame errors. These errors can often be solved with hardware upgrades. © 2006 Cisco Systems, Inc. All rights reserved.

Ways to Prevent Packet Loss § Upgrade the link (the best solution but also

Ways to Prevent Packet Loss § Upgrade the link (the best solution but also the most expensive). § Guarantee enough bandwidth for sensitive packets. § Prevent congestion by randomly dropping less important packets before congestion occurs. © 2006 Cisco Systems, Inc. All rights reserved.

Traffic Rate Policing Traffic Policing and Traffic Shaping Time Traffic Rate Shaping Time ©

Traffic Rate Policing Traffic Policing and Traffic Shaping Time Traffic Rate Shaping Time © 2006 Cisco Systems, Inc. All rights reserved. Traffic Time Traffic Rate Time

Reducing Packet Loss in a Network § Problem: Interface congestion causes TCP and voice

Reducing Packet Loss in a Network § Problem: Interface congestion causes TCP and voice packet drops, resulting in slowing FTP traffic and jerky speech quality. § Conclusion: Congestion avoidance and queuing can help. § Solution: Use WRED and LLQ. © 2006 Cisco Systems, Inc. All rights reserved.

Summary § Converged networks carry different types of traffic over a shared infrastructure. This

Summary § Converged networks carry different types of traffic over a shared infrastructure. This creates the need to differentiate traffic and give priority to time-sensitive traffic. § Various mechanisms exist that help to maximize the use of the available bandwidth, including queuing techniques and compression mechanisms. § All networks experience delay. Delay can effect time sensitive traffic such as voice and video. § Without proper provisioning and management, networks can experience packet loss. Packet loss is especially important with voice and video, as no resending of lost packets can occur. © 2006 Cisco Systems, Inc. All rights reserved.

3. 2: Implementing Qo. S © 2006 Cisco Systems, Inc. All rights reserved.

3. 2: Implementing Qo. S © 2006 Cisco Systems, Inc. All rights reserved.

Objectives § Describe the need for Qo. S as it relates to various types

Objectives § Describe the need for Qo. S as it relates to various types of network traffic. § Identify Qo. S mechanisms. § Describe the steps used to implement Qo. S. © 2006 Cisco Systems, Inc. All rights reserved.

What Is Quality of Service? Two Perspectives § The user perspective Users perceive that

What Is Quality of Service? Two Perspectives § The user perspective Users perceive that their applications are performing properly Voice, video, and data § The network manager perspective Need to manage bandwidth allocations to deliver the desired application performance Control delay, jitter, and packet loss © 2006 Cisco Systems, Inc. All rights reserved.

Different Types of Traffic Have Different Needs § Real-time applications especially sensitive to Qo.

Different Types of Traffic Have Different Needs § Real-time applications especially sensitive to Qo. S Application Examples Delay Jitter Packet Loss Interactive Voice and Video Y Y Y Streaming Video N Y Y Transactional/ Interactive Y N N Bulk Data Email File Transfer N N N Interactive voice Videoconferencing § Causes of degraded performance Congestion losses Sensitivity to Qo. S Metrics Variable queuing delays § The Qo. S challenge Manage bandwidth allocations to deliver the desired application performance Control delay, jitter, and packet loss © 2006 Cisco Systems, Inc. All rights reserved. Need to manage bandwidth allocations

Cisco IOS Qo. S Tools § Congestion management: PQ CQ WFQ CBWFQ § Queue

Cisco IOS Qo. S Tools § Congestion management: PQ CQ WFQ CBWFQ § Queue management WRED § Link efficiency Link fragmentation and interleave RTP and CRTP § Traffic shaping and traffic policing © 2006 Cisco Systems, Inc. All rights reserved. Qo. S Toolbox

Priority Queuing PQ puts data into four levels of queues: high, medium, normal, and

Priority Queuing PQ puts data into four levels of queues: high, medium, normal, and low. © 2006 Cisco Systems, Inc. All rights reserved.

Priority Queuing § Priority output queuing allows a network administrator to define four priorities

Priority Queuing § Priority output queuing allows a network administrator to define four priorities of traffic---high, normal, medium, and low---on a given interface. § As traffic comes into the router, it is assigned to one of the four output queues. § Packets on the highest-priority queue are transmitted first. © 2006 Cisco Systems, Inc. All rights reserved.

Priority Queuing ctd. . § When that queue empties, traffic on the next highestpriority

Priority Queuing ctd. . § When that queue empties, traffic on the next highestpriority queue is transmitted, and so on. § This mechanism assures that during congestion, the highest-priority data does not get delayed by lowerpriority traffic. § However, if the traffic sent to a given interface exceeds the bandwidth of that interface, lower-priority traffic can experience significant delays. © 2006 Cisco Systems, Inc. All rights reserved.

Custom Queuing CQ handles traffic by assigning a specified amount of queue space to

Custom Queuing CQ handles traffic by assigning a specified amount of queue space to each class of packet and then servicing up to 17 queues in a round-robin fashion. © 2006 Cisco Systems, Inc. All rights reserved.

Custom Queuing § Custom queuing allows a customer to reserve a percentage of bandwidth

Custom Queuing § Custom queuing allows a customer to reserve a percentage of bandwidth for specified protocols. § Customers can define up to 10 output queues for normal data and an additional queue for system messages such as LAN keepalive messages (routing packets are not assigned to the system queue). § The routers service each queue sequentially, transmitting a configurable percentage of traffic on each queue before moving on to the next one. § Custom Queuing guarantees that mission-critical data is always assigned a certain percentage of the bandwidth, but also assures predictable throughput for other traffic. © 2006 Cisco Systems, Inc. All rights reserved.

Custom Queuing … § To provide this feature, routers determine how many bytes should

Custom Queuing … § To provide this feature, routers determine how many bytes should be transmitted from each queue, based on the interface speed and the configured percentage. § When the calculated byte count from a given queue has been transmitted, the router completes transmission of the current packet and moves on to the next queue, servicing each queue in a round-robin fashion. © 2006 Cisco Systems, Inc. All rights reserved.

Weighted Fair Queuing • WFQ makes the transfer rates and interarrival periods of active

Weighted Fair Queuing • WFQ makes the transfer rates and interarrival periods of active high-volume conversations much more predictable. © 2006 Cisco Systems, Inc. All rights reserved.

Weighted Fair Queuing (Flow based) Flow-Based WFQ: Creating Fairness Among Flows § For situations

Weighted Fair Queuing (Flow based) Flow-Based WFQ: Creating Fairness Among Flows § For situations in which it is desirable to provide consistent response time to heavy and light network users alike without adding excessive bandwidth, the solution is flow-based WFQ (commonly referred to as just WFQ). § It is a flow-based queuing algorithm that creates bitwise fairness by allowing each queue to be serviced fairly in terms of byte count. © 2006 Cisco Systems, Inc. All rights reserved.

WFQ …. § For example, if queue 1 has 100 -byte packets and queue

WFQ …. § For example, if queue 1 has 100 -byte packets and queue 2 has 50 -byte packets, the WFQ algorithm will take two packets from queue 2 for every one packet from queue 1. § This makes service fair for each queue: 100 bytes each time the queue is serviced. § WFQ ensures that queues do not starve for bandwidth and that traffic gets predictable service. § Low-volume traffic streams that comprise the majority of traffic, receive increased service, transmitting the same number of bytes as high-volume streams. § This behavior results in what appears to be preferential treatment for low-volume traffic, when in actuality it is creating fairness. © 2006 Cisco Systems, Inc. All rights reserved.

Weighted Random Early Detection • WRED provides a method that stochastically discards packets if

Weighted Random Early Detection • WRED provides a method that stochastically discards packets if congestion begins to increase. © 2006 Cisco Systems, Inc. All rights reserved.

© 2006 Cisco Systems, Inc. All rights reserved.

© 2006 Cisco Systems, Inc. All rights reserved.

Implementing Qo. S Step 1: Identify types of traffic and their requirements. Step 2:

Implementing Qo. S Step 1: Identify types of traffic and their requirements. Step 2: Divide traffic into classes. Step 3: Define Qo. S policies for each class. © 2006 Cisco Systems, Inc. All rights reserved.

Step 1: Identify Types of Traffic and Their Requirements § Network audit: Identify traffic

Step 1: Identify Types of Traffic and Their Requirements § Network audit: Identify traffic on the network. § Business audit: Determine how important each type of traffic is for business. § Service levels required: Determine required response time. © 2006 Cisco Systems, Inc. All rights reserved.

Step 2: Define Traffic Classes Scavenger Class © 2006 Cisco Systems, Inc. All rights

Step 2: Define Traffic Classes Scavenger Class © 2006 Cisco Systems, Inc. All rights reserved. Less than Best Effort

Step 3: Define Qo. S Policy § A Qo. S policy is a network

Step 3: Define Qo. S Policy § A Qo. S policy is a network -wide definition of the specific levels of Qo. S that are assigned to different classes of network traffic. © 2006 Cisco Systems, Inc. All rights reserved.

Quality of Service Operations How Do Qo. S Tools Work? Classification and Marking ©

Quality of Service Operations How Do Qo. S Tools Work? Classification and Marking © 2006 Cisco Systems, Inc. All rights reserved. Queuing and (Selective) Dropping Post-Queuing Operations

Self Check 1. What types of applications are particularly sensitive to Qo. S issues?

Self Check 1. What types of applications are particularly sensitive to Qo. S issues? 2. What is WFQ? How is it different than FIFO? 3. What are the 3 basic steps involved in implementing Qo. S? 4. What is Scavenger Class? © 2006 Cisco Systems, Inc. All rights reserved.

Summary § Qo. S is important to both the end user and the network

Summary § Qo. S is important to both the end user and the network administrator. End users experience lack of Qo. S as poor voice quality, dropped calls or outages. § Network traffic differs in its ability to handle delay, jitter and packet loss. Traffic sensitive to these issues requires priority treatment. Qo. S measures can provide priority to sensitive traffic, while still providing services to more resilient traffic. § Implementing Qo. S involves 3 basic steps: identify the types of traffic on your network, divide the traffic into classes, and define a Qo. S policy for each traffic class. © 2006 Cisco Systems, Inc. All rights reserved.