© 2006 Cisco Systems, Inc. All rights reserved.ONT v1.03-1 Introduction to IP QoS Introducing QoS. - презентация

1 © 2006 Cisco Systems, Inc. All rights reserved.ONT v Introduction to IP QoS Introducing QoS

2 © 2006 Cisco Systems, Inc. All rights reserved.ONT v Converged Networks Quality Issues

3 © 2006 Cisco Systems, Inc. All rights reserved.ONT v Converged Network Quality Issues Converged traffic characteristics: Constant small-packet voice flow competes with bursty data flow. Critical traffic must get priority. Voice and video are time-sensitive. Brief outages are not acceptable.

4 © 2006 Cisco Systems, Inc. All rights reserved.ONT v Converged Network 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 increased delay. Packet loss: Packets may have to be dropped when a link is congested.

5 © 2006 Cisco Systems, Inc. All rights reserved.ONT v Available Bandwidth

6 © 2006 Cisco Systems, Inc. All rights reserved.ONT v Lack of Bandwidth Maximum available bandwidth equals 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.

7 © 2006 Cisco Systems, Inc. All rights reserved.ONT v Bandwidth Availability Upgrade the link (the best but also the most expensive solution). Forward the important packets first. Compress the payload of Layer 2 frames (it takes time). Compress IP packet headers.

8 © 2006 Cisco Systems, Inc. All rights reserved.ONT v Efficient Use of Available Bandwidth Using advanced queuing and header compression mechanisms, the available bandwidth can be used in a much more efficient way: Voice: LLQ and RTP header compression Interactive traffic: CBWFQ and TCP header compression

9 © 2006 Cisco Systems, Inc. All rights reserved.ONT v End-to-End Delay

10 © 2006 Cisco Systems, Inc. All rights reserved.ONT v Types of 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 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.

11 © 2006 Cisco Systems, Inc. All rights reserved.ONT v The Impact of Delay on Quality End-to-end delay equals the sum of all propagation, processing, serialization, and queuing delays in the path. Jitter defines the variation in the delay. In best-effort networks, propagation and serialization delays are fixed, while processing and queuing delays are unpredictable.

12 © 2006 Cisco Systems, Inc. All rights reserved.ONT v 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 (it takes time). Compress IP packet headers.

13 © 2006 Cisco Systems, Inc. All rights reserved.ONT v Efficient Use of Ways to Reduce Delay Customer routers perform: –TCP/RTP header compression –LLQ –Prioritization ISP routers perform: –Reprioritization according to the QoS policy

14 © 2006 Cisco Systems, Inc. All rights reserved.ONT v Packet Loss

15 © 2006 Cisco Systems, Inc. All rights reserved.ONT v Impact 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.

16 © 2006 Cisco Systems, Inc. All rights reserved.ONT v Impact of Packet Loss (Cont.) Tail drops occur when the output queue is full. Tail drops are common and happen when a link is congested. Many other types of drops occur, usually the result of router congestion, that are uncommon and may require a hardware upgrade (such as, input drop, ignore, overrun, frame errors).

17 © 2006 Cisco Systems, Inc. All rights reserved.ONT v Ways to Prevent Packet Loss Upgrade the link (the best solution but also the most expensive). Guarantee enough bandwidth to sensitive packets. Prevent congestion by randomly dropping less important packets before congestion occurs.

18 © 2006 Cisco Systems, Inc. All rights reserved.ONT v Packet Loss Solution 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.

19 © 2006 Cisco Systems, Inc. All rights reserved.ONT v QoS Defined

20 © 2006 Cisco Systems, Inc. All rights reserved.ONT v QoS Defined

21 © 2006 Cisco Systems, Inc. All rights reserved.ONT v Implementing QoS

22 © 2006 Cisco Systems, Inc. All rights reserved.ONT v Implementing QoS 1. Identify traffic and its requirements. 2. Divide traffic into classes. 3. Define QoS policies for each class.

23 © 2006 Cisco Systems, Inc. All rights reserved.ONT v QoS Traffic Classes The Requirements of Different Traffic Types

24 © 2006 Cisco Systems, Inc. All rights reserved.ONT v Identify Traffic and Its 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.

25 © 2006 Cisco Systems, Inc. All rights reserved.ONT v The Requirements of Different Traffic Types

26 © 2006 Cisco Systems, Inc. All rights reserved.ONT v QoS Policy

27 © 2006 Cisco Systems, Inc. All rights reserved.ONT v QoS Policy A networkwide definition of the specific levels of QoS assigned to different classes of network traffic

28 © 2006 Cisco Systems, Inc. All rights reserved.ONT v Summary Converged networks that support voice, video, and data create new requirements for managing network traffic. QoS meets those requirements. Converged networks suffer from different quality issues, including lack of adequate bandwidth, end-to-end and variable delay, and lost packets. Packet loss can adversely affect QoS in a network. QoS is a way to improve the performance of converged networks.

29 © 2006 Cisco Systems, Inc. All rights reserved.ONT v Summary (Cont.) Lack of recourses causes networks to experience different types of delay, including processing delay, queuing delay, serialization delay, and propagation delay. QoS traffic classes need to be defined to implement a QoS policy. Implementing QoS requires three steps: identify requirements, classify network traffic, and define networkwide policies for quality. A QoS policy is a networkwide definition of the specific levels of QoS assigned to classes of network traffic.

30 © 2006 Cisco Systems, Inc. All rights reserved.ONT v