© 2004 Cisco Systems, Inc. All rights reserved. Troubleshooting Voice Quality Issues Resolving Voice QoS Issues with Cisco QoS Tools IPTT v4.05-1. - презентация

1 © 2004 Cisco Systems, Inc. All rights reserved. Troubleshooting Voice Quality Issues Resolving Voice QoS Issues with Cisco QoS Tools IPTT v4.05-1

2 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Resolving Voice QoS Issues with Cisco QoS Tools Lesson Objectives Upon completing this lesson, you will be able to: Explain bandwidth issues that may impact voice quality. Explain the affects of jitter and latency on a voice call Identify latency and jitter effects List issues which may impact voice quality when using Frame Relay Networks Define the difference between traffic marking and traffic classification Demonstrate why Low Latency Queuing is the preferred method when transmitting voice calls over a slower speed link List and Explain the usages of link fragmentation and compression when transmitting a voice call over a WAN link

3 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Outline Overview Quality of Service Defined Converged Networks Converged Networks: Quality Issues Lack of Bandwidth End-to-End Delay Packet Loss QoS Requirements QoS Policy QoS for Converged Networks LAN QoS Considerations Summary Quiz

4 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Quality of Service Defined

5 © 2004 Cisco Systems, Inc. All rights reserved. IPTT 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 survivable

6 © 2004 Cisco Systems, Inc. All rights reserved. IPTT 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

7 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Converged Networks: Quality Issues Phone call: I cant understand you; your voice is breaking up. Teleconferencing: The picture is very jerky. Voice is not synchronized. Brokerage house: I needed that information two hours ago. Where is it? Call center: Please hold while my screen refreshes.

8 © 2004 Cisco Systems, Inc. All rights reserved. IPTT 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.

9 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Lack of Bandwidth The 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 (10 MB, 256 k, 512 k, 100 M) = 256 kbps BW avail = BW max /Flows Bad Voice Due to Lack of BW

10 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Ways to Increase Available Bandwidth

11 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Ways to Increase Available Bandwidth (Cont.) Upgrade the link. (Best solution, but also the most expensive)

12 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Ways to Increase Available Bandwidth (Cont.) Upgrade the link. (Best solution, but also the most expensive) Forward the important packets first.

13 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Ways to Increase Available Bandwidth (Cont.) Upgrade the link. (Best solution, but also the most expensive) Forward the important packets first. Compress the payload of Layer 2 frames (it takes time).

14 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Ways to Increase Available Bandwidth (Cont.) Upgrade the link. (Best solution, but also the most expensive) Forward the important packets first. Compress the payload of Layer 2 frames (it takes time). Compress the header of IP packets.

15 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Ways to Increase Available Bandwidth Upgrade the link. (Best solution, but also the most expensive) Forward the important packets first. Compress the payload of Layer 2 frames (it takes time). Compress the header of IP packets.

16 © 2004 Cisco Systems, Inc. All rights reserved. IPTT 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

17 © 2004 Cisco Systems, Inc. All rights reserved. IPTT 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

18 © 2004 Cisco Systems, Inc. All rights reserved. IPTT 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

19 © 2004 Cisco Systems, Inc. All rights reserved. IPTT 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

20 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Ways to Reduce Delay

21 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Ways to Reduce Delay (Cont.) Upgrade the link. (Best solution, but also the most expensive)

22 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Ways to Reduce Delay (Cont.) Upgrade the link. (Best solution, but also the most expensive) Forward the important packets first.

23 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Ways to Reduce Delay (Cont.) Upgrade the link. (Best solution, but also the most expensive) Forward the important packets first. Compress the payload of Layer 2 frames (it takes time).

24 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Ways to Reduce Delay (Cont.) Upgrade the link. (Best solution, but also the most expensive) Forward the important packets first. Compress the payload of Layer 2 frames (it takes time). Compress the header of IP packets.

25 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Ways to Reduce Delay Upgrade the link. (Best solution, but also the most expensive) Forward the important packets first. Compress the payload of Layer 2 frames (it takes time). Compress the header of IP packets.

26 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Packet Loss Tail drops occur when the output queue is full. These are common drops that 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

27 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Ways to Prevent Packet Loss

28 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Ways to Prevent Packet Loss (Cont.) Upgrade the link. (Best solution, but also the most expensive)

29 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Ways to Prevent Packet Loss (Cont.) Upgrade the link. (Best solution, but also the most expensive) Guarantee enough bandwidth to sensitive packets.

30 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Ways to Prevent Packet Loss (Cont.) Upgrade the link. (Best solution, but also the most expensive) Guarantee enough bandwidth to sensitive packets. Prevent congestion by randomly dropping less important packets before congestion occurs.

31 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Ways to Prevent Packet Loss Upgrade the link. (Best solution, but also the most expensive) Guarantee enough bandwidth to sensitive packets. Prevent congestion by randomly dropping less important packets before congestion occurs.

32 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v QoS Traffic Requirements: Voice Latency < 150 ms* Jitter < 30 ms* Loss < 1 percent* kbps guaranteed priority bandwidth per call 150 bps (+ Layer 2 overhead) guaranteed bandwidth for voice- control traffic per call * One-way requirements – – –

33 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Latency < 150 ms Jitter < 30 ms Loss < 1 percent Minimum priority bandwidth guarantee required is: –Video stream + 20 percent –For example: 384-kbps stream would require 460 kbps of priority bandwidth * One-way requirements QoS Traffic Requirements: Videoconferencing – – –

34 © 2004 Cisco Systems, Inc. All rights reserved. IPTT 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 a relative- priority model with no more than four to five classes: –Mission-critical applications: 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

35 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v QoS Policy A network-wide definition of the specific levels of quality of service assigned to different classes of network traffic

36 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v QoS Policy (Cont.) Align Network Resources with Business Priorities

37 © 2004 Cisco Systems, Inc. All rights reserved. IPTT 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 the required response time.

38 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Step 2: Divide the Traffic into Service Classes

39 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Step 3: Define Policies for Each Service Class Set minimum bandwidth guarantee. Set maximum bandwidth limits. Assign priorities to each class. Manage congestion.

40 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v LAN QoS Considerations Bandwidth is 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.

41 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Summary Quality of service is the ability of the network to provide better or special service to users or applications or both. 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 that can overcome the problems presented by a lack of bandwidth, delay, variable delay, and packet loss.

42 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Summary (Cont.) Voice, video, and data have very different QoS requirements to run effectively on a network. A QoS policy is a network-wide definition of the specific levels of QoS assigned to classes of network traffic. Building QoS requires three steps: identifying requirements, classifying network traffic, and defining network-wide policies for quality.

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