Call transfer is typically a feature that employees use to transfer from internal DNs to internal DNs. When calls are transferred to an external destination, very often the reason is that the caller whose call is transferred does not have permission to dial that external destination. The operator or an employee, for instance, could be asked to transfer a call of a colleague who is home on vacation to an international destination. Or an employee who is not allowed to call international numbers could ask a colleague who is allowed to call international numbers to transfer the call to that international number. An employee could also save money by having family members call the employee in the office when they need to place costly calls. All that the employee has to do is to transfer the call for them. To eliminate the cost of their call to the office of the employee, the employee could even hang up and call them back before transferring the call.
You can configure Cisco CallManager to block external-to-external call transfers. This configuration involves setting a simple service parameter and configuring gateways, trunks, and route patterns as OffNet (external) devices. After you have configured this, external-to-external call transfers will not be allowed. This feature provides an OnNet or OffNet alerting tone to the terminating end of the call (determined by the configuration of the device as either OnNet or OffNet). For incoming calls, trunks or gateways determine OffNet versus OnNet classification. For outgoing calls, the route pattern determines OffNet versus OnNet status.
The external call transfer restriction requires the Cisco CallManager Release 4.1 or later software component.
Defining OnNet and OffNet
Cisco CallManager classifies internal and external calls as OnNet and OffNet. A call coming from an external PSTN is classified as an OffNet call. A call that is placed internally (from one telephone to another, or between two Cisco CallManager clusters, where the call is routed over the WAN) is classified as an OnNet call, as illustrated in Figure 22-5. When you are using Automated Alternate Routing (AAR) in OnNet or OffNet implementations, it is important to know from where the call is coming. With AAR, the source can be either the WAN connection or the PSTN connection. This can cause restrictions when a call is rerouted. For example, if a user attempts to call across the IP WAN and AAR reroutes the call through the PSTN, the called party will not be able to transfer the call to another external phone number due to the Block OffNet to OffNet Transfers service parameter.
Figure 22-5. OnNet Versus OffNet Calls
You can configure gateways and trunks as OnNet (internal) or OffNet (external) by using gateway configuration, using trunk configuration, or setting a clusterwide service parameter to classify devices automatically. When the feature is used in conjunction with the clusterwide service parameter Block OffNet to OffNet Transfer, the configuration determines whether calls can transfer over a gateway or trunk.
These devices can be configured as OnNet and OffNet to Cisco CallManager, as shown in Figure 22-6:
Figure 22-6. Configuring a Gateway as OnNet or OffNet
By default, all gateways use OffNet classification.
To classify an outgoing call as OnNet or OffNet, you can set the Call Classification field in the Route Pattern Configuration window to OnNet or OffNet, as shown in Figure 22-7. You can override the route pattern setting and use the trunk or gateway setting by checking the Allow Device Override check box in the Route Pattern Configuration window. All route patterns default to OffNet if the Provide Outside Dial Tone check box is checked. If the check box is unchecked, the route pattern defaults to OnNet.
Figure 22-7. Configuring a Route Pattern as OnNet or OffNet
Configuring Call Transfer Restrictions
Now that you have seen the method used to categorize gateways and route patterns, you can complete these steps to block external calls from being transferred to external devices:
You can specify the OnNet or OffNet classification on the following:
For incoming calls, configure individual gateways or trunks as OffNet.
For outgoing calls, configure the route pattern Call Classification field as OffNet. Note that you can choose the Allow Device Override check box under the route pattern to allow the associated gateway to dictate whether the outgoing call is OnNet or OffNet.
Set the Block OffNet to OffNet Transfer clusterwide CallManager service parameter shown in Figure 22-8 to True.
Figure 22-8. Setting the Block OffNet to OffNet Service Parameter
Call Transfer Restriction Example
In the Cisco CallManager configuration shown in Figure 22-9, the route pattern that is used to reach the external destinations is classified as an OffNet pattern. The gateway is also classified as OffNet. The service parameter Block OffNet to OffNet Transfer in the Cisco CallManager service parameters is set to True. Thus, the attempt by party A to call party B and transfer the call to party C will not work because OffNet-to-OffNet call transfers are restricted.
Figure 22-9. Blocking OffNet-to-OffNet Calls
Dropping Conference Calls
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