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| 7.4 |  | Cisco IP Telephony |
| 7.4.6 |  | Multisite IP WAN with centralized call processing |

The multisite IP WAN with centralized call processing has the following design characteristics:

- Central site supports only one active Cisco CallManager. A cluster can contain a secondary and tertiary Cisco CallManager as long as all IP phones served by the cluster are registered to the same Cisco CallManager at any given time. This is called a centralized call processing cluster
- Each centralized call processing cluster supports a maximum of 2500 users (no limit on number of remote sites). Multiple centralized call processing clusters of 2500 users at a central site can be interconnected using H.323
- IP phones at remote sites do not have a local Cisco CallManager
- The call admission control mechanism is based on bandwidth by location
- Compressed voice calls across the IP WAN are supported
- Manual use of the PSTN is available if the IP WAN is fully subscribed for voice traffic (PSTN access code must be dialed after a busy signal)
- Dial backup is required for IP phone service across the WAN in case the IP WAN goes down
- Voice mail, unified messaging, and DSP resource components are available at the central site only
- Minimum bandwidth requirement for voice and data traffic is 56 kbps. For voice, interactive video, and data, the minimum requirement is 768 kbps. In each case, the bandwidth allocated to voice, video, and data should not exceed 75% of the total capacity
- Remote sites can use Cisco IOS as well as gateways based on the Skinny Station Protocol
- If using voice mail, each site must have unique internal dial plan number ranges. Internal dial plans cannot be overlapped among remote sites if voice mail is required, no two sites can share 1XXX.

| Interactive Media Activity Checkbox: Cisco IP Telephony Designs After completing this activity, the students will be able to understand Cisco IP telephony designs.