Cisco Systems OL-14619-01 manual Audio Codecs, How Codecs Affect the File Size of Voice Messages

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Chapter 3 Network Infrastructure Requirements

Audio Codecs

In some cases you might find that an existing voice messaging system has more ports than the current maximum number of voice ports on a Cisco Unity system. In this case, the customer can purchase additional Cisco Unity servers and connect them by using Cisco Unity Digital Networking.

Audio Codecs

An audio codec is an algorithm that encodes and decodes (and compresses or decompresses) audio data. Cisco Unity uses audio codecs with streaming (live conversation) and for WAV-file voice messages. Cisco Unity supports the following audio codecs:

•G.711 Mu-Law (the default codec)

•G.711 A-Law

•G.729a

•Intel Dialogic OKI ADPCM 8 kHz

•Intel Dialogic OKI ADPCM 6 kHz

•GSM 6.10

•G.726 codec (supported only when using VPIM to communicate with another voice-messaging system)

In general, choose an audio codec based on available storage capacity for voice messages and on available network bandwidth. We recommend using G.711 whenever possible because of its excellent quality for recording and playback. However, if other considerations prevent the customer from using G.711, it is fine to use G.729a, which is also a voice-quality codec. (A large-scale or multiserver deployment may require the use of more than one codec.)

The rest of this section discusses some of the issues to consider when choosing a codec. For a more thorough analysis, see the Audio Codecs and Cisco Unity white paper at http://www.cisco.com/en/US/products/sw/voicesw/ps2237/prod_white_papers_list.html.

For information on how codec choice affects Active Directory, see the applicable Active Directory Capacity Planning white paper at http://www.cisco.com/en/US/products/sw/voicesw/ps2237/prod_white_papers_list.html.

How Codecs Affect the File Size of Voice Messages

Stored voice messages can consume considerable amounts of disk space. The amount of storage a WAV file uses depends on what kind of compression the codec uses, if any. The higher the compression, the smaller the file and the smaller the disk-space impact on the database and at the subscriber workstation. However, some sound-quality reduction and some CPU processing overhead may result when compressing messages during recording and decompressing at playback.

As illustrated in Table 3-1, voice messages that are recorded in G.711 Mu-Law and A-Law require the most disk space to store, while G.729a offers the smallest file size.

Note Audio quality ratings are subjective, and are provided here only for basic comparison between the different fully supported codecs.

Design Guide for Cisco Unity Release 5.x

 

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Contents Americas Headquarters Design Guide for Cisco UnityDesign Guide for Cisco Unity Release N T E N T S Workstations Authentication Centralized Voice Messaging Configuration Viii Document Conventions AudienceSupport Policy for Optional Third-Party Software Cisco Product Security Overview Xii Design Guide Overview Product Area Design or Feature DocumentationDesign Guide for Cisco Unity Bridge at Page Design Guide Overview Design Guide for Cisco Unity Release How Cisco Unity Works Cisco Unity ConceptsVoice Messaging Unified MessagingHardware Components of a Cisco Unity System Cisco Unity Supported Platforms List at One or More Cisco Unity ServersNetwork Connection Optional for Some Configurations Domino Where Cisco Unity Stores DataSoftware Components of a Cisco Unity System Voice Messages Are Stored in Domino or ExchangeExchange Enabling Cisco Unity Servers to Communicate with One Another Networking Guide for Cisco Unity at Some Configuration Settings Are Stored in the Registry Availability of Network Resources Name ResolutionAvailability of Message Store Servers Domain Controller Access and AvailabilitySizing and Scaling Cisco Unity Servers Using Firewalls with Cisco UnityNumber of Voice Ports Storage Capacity for Voice MessagesHow Codecs Affect the File Size of Voice Messages Audio CodecsQuality Rating TTS, TTY, Pocket PCs, and Hand-Held ComputersInteroperability Among Multiple Voice-Messaging Systems Audio CodecDeployment Models Unified Messaging with Customer-Provided Infrastructure Multi-Site WAN with Distributed Messaging Voice Messaging with Customer-Provided InfrastructurePhysical Placement and Network Infrastructure Active Directory Considerations Considerations for Customer-Provided InfrastructureDesign Guide for Cisco Unity Release Exchange Considerations All Versions Exchange Considerations That Apply Only Exchange Considerations for Cisco-Provided, Dedicated Infrastructure OL-14619-01 Overview of Cisco Unity with Domino and Notes Domino Address Book Terminology Maximum Number of Cisco Unity SubscribersElement Name Changes That csAdmin Makes to the Domino Address BookChanges That csClient Makes to the Mail File Windows Domains and Domino Domains Server PlacementActive Directory Accounts and Permissions AuthenticationCisco Unity Subscribers and Domino Users Domino PermissionsDomino Clusters Backing Up and Restoring Data Client Access LicensesCisco Unity and the Domino Address Book Message RoutingUnified Messaging, No Domino Cluster Unified Messaging ConfigurationsServers Requirements and Recommendations Criteria for a Supported Configuration Voice Messaging ConfigurationUnified Messaging, Domino Cluster Deploying Cisco Unity for Lotus Domino Establishing Support Policies Administrative Access and ControlNetwork Services Deployment Tasks for Unified Messaging ConfigurationsOperational Tasks Design Guide for Cisco Unity Release Overview Integrating Cisco Unity with the Phone SystemHow an Integration Works Integration with Cisco Unified Communications Manager Lines and Cables to Make Physical ConnectionsDigital Integration with Digital Pimg Units Dtmf Integration with Analog Pimg Units LAN/WAN Timg IntegrationSerial Integration with Voice Cards Dtmf Integration with Voice CardsConnections for a Serial Integration by Using Voice Cards Settings in the Phone System and in Cisco UnityCall Control General Integration Issues Sccp SIP FeatureIntegrating Cisco Unity with the Phone System Option Considerations Description Cisco Unified Communications Manager Security FeaturesDescription Setting Effect When Data Is EncryptedDisabling and Re-Enabling Security Settings for Individual Voice Messaging PortsPacketization Sccp Integrations Only Sccp SIP Cisco 11 Cisco Unified Communications Manager Fallback with Pstn Cisco Unity to a branch office will fail Integrating by Using SIP Cisco Unity Failover with SIP Trunks Supported SIP IntegrationsSIP Compliance Description of Pimg Integrations Dtmf Integration with Analog Pimg Units Description of Timg Integrations Firmware Updates Serial Integrations Setup and ConfigurationCisco Unity Failover Increasing Port CapacityMultiple Integration Support/Branch Office Consolidation Cisco Unity FailbackIntegrating with Multiple Phone Systems Requirements for Integrations with Multiple Phone Systems Using Sccp Phone Systems with Other IntegrationsHow Alternate Extensions Work Optional Integration FeaturesAlternate Extensions Reasons to Use Alternate ExtensionsMWIs for Extensions on a Non-Integrated Phone System Alternate MWIsCentralized Voice Messaging OL-14619-01 OL-14619-01 Failover Cisco Unity Failover and Standby RedundancyStandby Redundancy Cisco Unity Failover and Standby Redundancy Cisco Unity Failover and Standby Redundancy Pstn WAN Diagram of a Standby Redundancy ConfigurationOL-14619-01 Voice-Recognition Access to Cisco Unity OL-14619-01 Migrating to Cisco Unity from Another Voice-Messaging System Migrating to Cisco Unity from Another Voice-Messaging System D E IN-2 IN-3 IN-4
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