configuring campus switches to support voice

© 2006 Cisco Systems, Inc. All rights reserved. Cisco ConfidentialBCMSN 7 - 1 1

Configuring Campus Switches to Support Voice

BCMSN Module 7 Lesson 1


Objectives

Explain why an organization would want to run VoIP on the network Describe the main components of a VoIP network, including IP-enabled PBX, user

end-devices, gateways and gatekeepers, and the IP network Compare the uniform bandwidth consumption of voice traffic to the intermittent

bandwidth consumption of data traffic Describe a VoIP call flow through a network and where contention for bandwidth

between data traffic and voice traffic will occur Explain an auxiliary VLAN Identify a solution for latency, jitter, bandwidth, packet loss, reliability, and security Explain the importance of high availability in the campus network to support a VoIP

implementation Explain the use of AutoQoS in Cisco Catalyst switches Describe the commands that enable AutoQoS on Cisco Catalyst switches


Purpose of this Lesson

Coverage of topics new to the “Configuring Campus Switches to Support Voice and Video Applications” module of BCMSN.

What’s new in this module?More information about Converged Networks.

Updated content for VoIP components and functionality.

Description of traffic types and call flow for VoIP.

New auto qos commands for voice.

Overall content is updated and reorganized.

This lesson does not cover QoS. The QoS module of BCMSN is largely unchanged.


The Basics

VoIP is a technology that digitizes sound, divides that sound into packets, and transmits those packets over an IP network.

VoIP evolved into IP telephony, delivering packetization to the desktop through IP phones. IP telephony uses telephone-like handsets, and users dial regular telephone numbers.

IP Communications, also called unified communications or converged communications, is the next stage in the evolution. Tying together telephone, voice mail, e-mail, and information services, via familiar-looking telephone equipment.


Benefits of a Converged Network

More efficient use of bandwidth and equipment

Lower transmission costs

Consolidated network expenses

Increased revenue from new services

Service innovation

Access to new communications devices

Flexible new pricing structures


VoIP Network Components


VoIP Call Flow


Codecs

A codec (Coder/Decoder) converts analog signals to a digital bitstream, and another identical codec at the far end of the communication converts the digital bitstream back into an analog signal.

Codecs generally provide a compression capability to save network bandwidth.


Auxiliary VLANs


Self Check

1. What is a codec used for in VoIP?

2. Which VoIP component provides translation between VoIP and non-VoIP networks?

3. What is call control signaling?

4. What protocol is used to carry actual voice samples?

5. What is the auxiliary VLAN feature supported by some Catalyst switches?


QoS


Converged Networks Require QoS

Traditional telephony networks reserve resources and guarantee voice quality.

Traditional data networks are best effort, with no guarantee of delivery, delay or timing. Depend on TCP upper-layer protocols for reliability.

Converged networks must use QoS to ensure that voice and data can be supported on the same network.


Characteristics of Voice and Data


Voice QoS RequirementsProvisioning for Voice

Latency ≤ 150 ms

Jitter ≤ 30 ms

Loss ≤ 1%

17–106 kbps guaranteed priority bandwidth per call

150 bps (+ layer 2 overhead) guaranteed bandwidth forvoice-control traffic per call

CAC (call admission control) must be enabled

• Smooth

• Benign

• Drop sensitive

• Delay sensitive

• UDP priority

VoiceOne-Way

Requirements


QoS Basics


AutoQoS

One command per interface to enable and configure QoS.


AutoQoS Benefits

Application Classification

Policy Generation

Configuration

Monitoring and Reporting

Consistency


Configuring AutoQoS

Single command at the interface level configures interface and global QoS.

Supported on static, dynamic-access, voice VLAN access, and trunk ports.

CDP must be enabled for AutoQoS to function properly.


AutoQoS VoIP for Catalyst Switches!mls qos map cos-dscp 0 8 16 26 32 46 48 56mls qos srr-queue output cos-map queue 1 threshold 3 5mls qos srr-queue output cos-map queue 2 threshold 3 3 6 7mls qos srr-queue output cos-map queue 3 threshold 3 2 4mls qos srr-queue output cos-map queue 4 threshold 2 1mls qos srr-queue output cos-map queue 4 threshold 3 0mls qos srr-queue output dscp-map queue 1 threshold 3 40 41 42 43 44 45 46 47mls qos srr-queue output dscp-map queue 2 threshold 3 24 25 26 27 28 29 30 31mls qos srr-queue output dscp-map queue 2 threshold 3 48 49 50 51 52 53 54 55mls qos srr-queue output dscp-map queue 2 threshold 3 56 57 58 59 60 61 62 63mls qos srr-queue output dscp-map queue 3 threshold 3 16 17 18 19 20 21 22 23mls qos srr-queue output dscp-map queue 3 threshold 3 32 33 34 35 36 37 38 39mls qos srr-queue output dscp-map queue 4 threshold 1 8mls qos srr-queue output dscp-map queue 4 threshold 2 9 10 11 12 13 14 15mls qos srr-queue output dscp-map queue 4 threshold 3 0 1 2 3 4 5 6 7mls qos queue-set output 1 threshold 1 138 138 92 138mls qos queue-set output 1 threshold 2 138 138 92 400mls qos queue-set output 1 threshold 3 36 77 100 318mls qos queue-set output 1 threshold 4 20 50 67 400mls qos queue-set output 2 threshold 1 149 149 100 149mls qos queue-set output 2 threshold 2 118 118 100 235mls qos queue-set output 2 threshold 3 41 68 100 272mls qos queue-set output 2 threshold 4 42 72 100 242mls qos queue-set output 1 buffers 10 10 26 54mls qos queue-set output 2 buffers 16 6 17 61mls qos!!interface GigabitEthernet0/1 srr-queue bandwidth share 10 10 60 20 srr-queue bandwidth shape 10 0 0 0 queue-set 2 mls qos trust device cisco-phone mls qos trust cos auto qos voip cisco-phone!

CAT2970(config-if)#auto qos voip cisco-phone


AutoQoS VoIP: WANinterface Serial2/0 bandwidth 768 ip address 10.1.102.2 255.255.255.0 encapsulation ppp auto qos voip trust

!interface Multilink2001100117 bandwidth 768 ip address 10.1.102.2 255.255.255.0 service-policy output AutoQoS-Policy-Trust ip tcp header-compression iphc-format no cdp enable ppp multilink ppp multilink fragment delay 10 ppp multilink interleave ppp multilink group 2001100117 ip rtp header-compression iphc-format!…!interface Serial2/0 bandwidth 768 no ip address encapsulation ppp auto qos voip trust no fair-queue ppp multilink ppp multilink group 2001100117!

! class-map match-any AutoQoS-VoIP-RTP-Trust match ip dscp ef class-map match-any AutoQoS-VoIP-Control-Trust match ip dscp cs3 match ip dscp af31!! policy-map AutoQoS-Policy-Trust class AutoQoS-VoIP-RTP-Trust priority percent 70 class AutoQoS-VoIP-Control-Trust bandwidth percent 5 class class-default fair-queue!


Configuring AutoQoS: Native OS

auto qos voip trustauto qos voip trust

Switch(config-if)#

The uplink interface is connected to a trusted switch or router, and the VoIP classification in the ingress packet is trusted.

auto qos voip cisco-phoneauto qos voip cisco-phone

Switch(config-if)#

Automatically enables the trusted boundary feature, which uses the CDP to detect the presence or absence of a Cisco IP Phone.

If the interface is connected to a Cisco IP Phone, the QoS labels of incoming packets are trusted only when the Cisco IP Phone is detected.


Monitoring AutoQoS

show auto qos [interface interface-id]show auto qos [interface interface-id]

Switch#

Switch#show auto qosInitial configuration applied by AutoQoS:wrr-queue bandwidth 20 1 80 0 no wrr-queue cos-map wrr-queue cos 1 0 1 2 4 wrr-queue cos 3 3 6 7 wrr-queue cos 4 5 mls qos map cos-dscp 0 8 16 26 32 46 48 56 ! interface FastEthernet0/3 mls qos trust device cisco-phone mls qos trust cos

Displays the AutoQoS configuration that was initially applied

Does not display any user changes to the configuration that might be in effect


Self Check

1. Describe the characteristics of a traditional data network.

2. Describe the QoS requirements of voice traffic.

3. What 3 QoS quality factors directory affect voice quality?

4. What is the Cisco Auto QoS feature?

5. What Cisco protocol must be enabled for AutoQoS to function properly?


Summary

Converged networks reduce costs and increase productivity.

VoIP equipment consists of a VoIP phone and a network infrastructure capable of supporting VoIP.

Auxiliary VLANs provide the ability to apply QoS to voice traffic without affecting the flow of data from the client PC.

To ensure high quality VoIP, implementation of QoS is required.

AutoQoS is a simple way to implement a trust boundary for VoIP.


Q and A


Resources

FCC VoIP Frequently Asked Questionshttp://www.fcc.gov/voip/

VoIP Provider Informationhttp://voipreview.org/faq.aspx

Cisco Press Book: “Internet Phone Services Simplified”, by Jim Doherty, Neil Anderson, 2006.

configuring campus switches to support voice

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