Although the SQL 2000 database shared between CallManagers in your cluster provides a listing of all extensions that a user can dial within the cluster, you must manually add connections and route patterns to remote clusters before they can be reached. The connection type that acts as the road between CallManager clusters is the intercluster trunk. Depending on the size of your IP telephony network, you can create trunks directly between CallManager clusters or you can create trunks to connect to an H.323 gatekeeper.
You can create a network of enormous size using only intercluster trunks; however, because the trunks are a full-mesh configuration, it can become increasingly difficult to manage the larger your network gets. Intercluster trunks also lack the ability to perform call admission control, which could result in the WAN becoming swamped with VoIP traffic.
A gatekeeper provides call admission control by using the H.225 Registration, Admission, and Status (RAS) protocol message set that is used as a central point for call admission control, bandwidth allocation, and dial pattern resolution (call routing). The gatekeeper provides these services for communications between Cisco CallManager clusters and H.323 networks. Note that the voice path is between the endpoints; no RTP audio travels through the gatekeeper.
You can configure gatekeepers and trunks in Cisco CallManager Administration to function in either of the following ways:
Figure 9-4. Nongatekeeper-Controlled Trunk Design
Figure 9-5. Gatekeeper-Controlled Trunk Design
This configuration works well in large and smaller systems. For large systems in which many clusters exist, this configuration helps to avoid the configuration of individual Intercluster Trunks between each cluster. To use this method, choose Device > Trunk and choose Inter-Cluster Trunk (Gatekeeper Controlled) in Cisco CallManager Administration.
If you configure gatekeeper-controlled trunks, Cisco CallManager automatically creates a virtual trunk device. The IP address of this device changes dynamically to reflect the IP address of the remote device as determined by the gatekeeper.
Complete these steps to configure a nongatekeeper-controlled intercluster trunk:
Choose Trunk from the Device menu in the Cisco CallManager Administration window.
Click the Add a New Trunk link and choose Inter-Cluster Trunk (Non-Gatekeeper Controlled) from the Trunk Type drop-down menu.
Cisco CallManager populates the Device Protocol field with the appropriate protocol. Click Next to continue.
The Trunk Configuration window appears, as shown in Figure 9-6. Add the device name. It does not have to be the IP address, but it must be unique throughout the cluster.
Figure 9-6. CallManager Nongatekeeper-Controlled intercluster trunk Configuration
At the bottom of the Trunk Configuration window, you can add the IP addresses of up to three Cisco CallManager servers in the remote cluster. You must add the IP address for at least one remote CallManager.
Configuring gatekeeper-controlled intercluster trunks is covered in Chapter 14, "Implementing Multiple-Site Deployments."
SIP and Cisco CallManager
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