Call forwarding (for busy, no-answer, and unconditional forwarding) raises many of the same issues as call transfer. Likewise, these issues can be addressed using an MTP to simplify the H.323 signaling operations.
As you read in Chapter 7, the preferred method of handling call forwarding for Cisco CME is H.450.3. Again, Cisco CME can disable its H.450.3 feature when it detects calls from a Cisco CallManager. Under these circumstances, the Cisco CME system falls back to using internal call forwarding or VoIP-to-VoIP call routing for intersite call forwarding.
Just like the call-transfer case, an MTP allows internal call forwarding to occur without impact to the H.323 call leg. Of the three types of forwardingbusy, no-answer, and unconditionalthe no-answer form generally involves more signaling complexity. When a call forward no-answer occurs, the preliminary call negotiation for the original called phone must be revoked (after the no-answer timeout). It is replaced with a new call to the forward-to destination phone. The forwarded call can potentially require the use of different parameters than those negotiated for the original called phone. The busy and unconditional forms of call forwarding usually don't involve a preliminary call actually reaching the forwarding phone; this tends to simplify the signaling. Figure 8-6 shows call forwarding between a Cisco CME system and a Cisco CallManager using MTP.
Figure 8-6. Cisco CallManager and Cisco CME Call Forwarding with MTP
You can see that Figure 8-4, which shows call transfer, and Figure 8-6, which shows call forwarding, are nearly identical. Figure 8-7 shows intersite Cisco CME call forwarding for a call from a Cisco CallManager. Compare it to Figure 8-5 for the equivalent call transfer case.
Figure 8-7. Cisco CallManager Forwarding with Multiple Cisco CMEs
For the special case of call forwarding to a voice mail system, note that the H.323 call setup for the forwarded call includes the original called number (the number of the forwarding phone). This can be used to provide integration with the voice mail system and to allow automatic selection of the voice mailbox that belongs to the forwarding phone.
Connected Party Name and Number Services
Part I: Cisco IP Communications Express Overview
Introducing Cisco IPC Express
Building a Cisco IPC Express Network
Cisco IPC Express Architecture Overview
Part II: Feature Operation and Applications
Cisco IP Phone Options
Cisco CME Call Processing Features
Cisco CME PSTN Connectivity Options
Connecting Multiple Cisco CMEs with VoIP
Integrating Cisco CME with Cisco CallManager
Cisco IPC Express Automated Attendant Options
Cisco IPC Express Integrated Voice Mail
Cisco CME External Voice Mail Options
Additional External Applications with Cisco CME
Part III: Administration and Management
Cisco IPC Express General Administration and Initial System Setup
Configuring and Managing Cisco IPC Express Systems
Cisco IPC Express System Configuration Example
Part IV: Maintenance and Troubleshooting
Troubleshooting Basic Cisco IPC Express Features
Troubleshooting Advanced Cisco CME Features
Troubleshooting Cisco CME Network Integration
Troubleshooting Cisco UE System Features
Troubleshooting Cisco UE Automated Attendant
Troubleshooting Cisco UE Integrated Voice Mail Features
Part V: Appendixes
Appendix A. Cisco IPC Express Features, Releases, and Ordering Information
Appendix B. Sample Cisco UE AA Scripts
Appendix C. Cisco Unity Express Database Schema