Configuring an IOS-based gatekeeper eliminates the need to configure a full-mesh Intercluster Trunk relationship between disparate Cisco CallManager clusters in your organization. Instead, all the clusters can trunk directly to the H.323 gatekeeper, which provides a centralized point of admission and bandwidth control.
Router-based QoS mechanisms are not designed to handle CAC. If the CallManager routes too many calls over the IP WAN, the voice quality for all calls will degrade.
B and D
In a distributed call-control environment, an independent device is needed to manage admission and bandwidth control. This responsibility falls on the H.323 gatekeeper device. The Cisco CallManager only manages these functions in a centralized call deployment.
The IP Phones are assigned to a device pool, which points to an SRST Reference. This SRST Reference contains the IP address of the gateway running SRST or points the IP Phone to its default gateway. This configuration is sent to the IP Phone when it first registers with the Cisco CallManager.
Cisco CallManager deducts 24 kbps for each call in a location-based CAC deployment. Using this calculation, you can find that five calls consume 120 kbps, fitting nicely over a 128-kbps connection.
A, B, and E
When AAR reroutes a call over the PSTN, CallManager takes the original DN of the IP Phone and combines it with the external phone number mask. The resulting number is then prepended with whatever additional digits are specified under the AAR group and forwarded over the PSTN.
To configure SRST, you first enter the command call-manager-fallback from global configuration mode. The router then places you in a subconfiguration mode where the additional settings can be specified.
AAR will use the external phone number mask configured under Phone B's DN to complete the call. This mask prepends the necessary digits to the DN, at which point the AAR group prepends any additional digits that might be required to exit the PSTN gateway and CallManager routes the call across the PSTN.
Before AAR configurations can take effect, the feature must be enabled clusterwide. This is accomplished from the Service > Service Parameters > Cisco CallManager Configuration window.
AAR is meant to act as a call redirection mechanism for location-based bandwidth restrictions. It does not reroute calls during a WAN failure. Although any of these answers could cause AAR redirection to fail, answer D is the most likely explanation.
Part I: Cisco CallManager Fundamentals
Introduction to Cisco Unified Communications and Cisco Unified CallManager
Cisco Unified CallManager Clustering and Deployment Options
Cisco Unified CallManager Installation and Upgrades
Part II: IPT Devices and Users
Cisco IP Phones and Other User Devices
Configuring Cisco Unified CallManager to Support IP Phones
Cisco IP Telephony Users
Cisco Bulk Administration Tool
Part III: IPT Network Integration and Route Plan
Cisco Catalyst Switches
Configuring Cisco Gateways and Trunks
Cisco Unified CallManager Route Plan Basics
Cisco Unified CallManager Advanced Route Plans
Configuring Hunt Groups and Call Coverage
Implementing Telephony Call Restrictions and Control
Implementing Multiple-Site Deployments
Part IV: VoIP Features
Configuring User Features, Part 1
Configuring User Features, Part 2
Configuring Cisco Unified CallManager Attendant Console
Configuring Cisco IP Manager Assistant
Part V: IPT Security
Securing the Windows Operating System
Securing Cisco Unified CallManager Administration
Preventing Toll Fraud
Hardening the IP Phone
Understanding Cryptographic Fundamentals
Understanding the Public Key Infrastructure
Understanding Cisco IP Telephony Authentication and Encryption Fundamentals
Configuring Cisco IP Telephony Authentication and Encryption
Part VI: IP Video
Introducing IP Video Telephony
Configuring Cisco VT Advantage
Part VII: IPT Management
Introducing Database Tools and Cisco Unified CallManager Serviceability
Configuring Alarms and Traces
Using Additional Management and Monitoring Tools
Part VIII: Appendix
Appendix A. Answers to Review Questions